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Molecular mechanisms of brain water transport

Abstract

Our brains consist of 80% water, which is continuously shifted between different compartments and cell types during physiological and pathophysiological processes. Disturbances in brain water homeostasis occur with pathologies such as brain oedema and hydrocephalus, in which fluid accumulation leads to elevated intracranial pressure. Targeted pharmacological treatments do not exist for these conditions owing to our incomplete understanding of the molecular mechanisms governing brain water transport. Historically, the transmembrane movement of brain water was assumed to occur as passive movement of water along the osmotic gradient, greatly accelerated by water channels termed aquaporins. Although aquaporins govern the majority of fluid handling in the kidney, they do not suffice to explain the overall brain water movement: either they are not present in the membranes across which water flows or they appear not to be required for the observed flow of water. Notably, brain fluid can be secreted against an osmotic gradient, suggesting that conventional osmotic water flow may not describe all transmembrane fluid transport in the brain. The cotransport of water is an unconventional molecular mechanism that is introduced in this Review as a missing link to bridge the gap in our understanding of cellular and barrier brain water transport.

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Fig. 1: Brain fluid movement and aquaporin expression.
Fig. 2: Water transport via cotransporters and aquaporins.
Fig. 3: Glial cells swell during activity-evoked K+ release from neurons.
Fig. 4: Neuronal swelling during cortical spreading depolarization presents as dendritic beading.
Fig. 5: Mechanisms of CSF secretion in choroid plexus.
Fig. 6: Osmoregulation in the brain.

References

  1. 1.

    Brightman, M. W. The distribution within the brain of ferritin injected into cerebrospinal fluid compartments. I. Ependymal distribution. J. Cell Biol. 26, 99–123 (1965).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  2. 2.

    Mathiisen, T. M., Lehre, K. P., Danbolt, N. C. & Ottersen, O. P. The perivascular astroglial sheath provides a complete covering of the brain microvessels: an electron microscopic 3D reconstruction. Glia 58, 1094–1103 (2010).

    PubMed  Article  PubMed Central  Google Scholar 

  3. 3.

    Mollgard, K., Balslev, Y., Lauritzen, B. & Saunders, N. R. Cell junctions and membrane specializations in the ventricular zone (germinal matrix) of the developing sheep brain: a CSF-brain barrier. J. Neurocytol. 16, 433–444 (1987).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  4. 4.

    Brightman, M. W. & Reese, T. S. Junctions between intimately apposed cell membranes in the vertebrate brain. J. Cell Biol. 40, 648–677 (1969).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  5. 5.

    Cserr, H. F., Cooper, D. N., Suri, P. K. & Patlak, C. S. Efflux of radiolabeled polyethylene glycols and albumin from rat brain. Am. J. Physiol. 240, F319–F328 (1981).

    CAS  PubMed  PubMed Central  Google Scholar 

  6. 6.

    His, W. Über ein perivasculäres canalsystem in den nervösen centralorganen und über dessen beziehungen sum lymphsystem. Z. für wissenschaftliche Zoologie 15, 127–141 (1865).

    Google Scholar 

  7. 7.

    Rennels, M. L., Blaumanis, O. R. & Grady, P. A. Rapid solute transport throughout the brain via paravascular fluid pathways. Adv. Neurol. 52, 431–439 (1990).

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8.

    Iliff, J. J. et al. A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid beta. Sci. Transl. Med. 4, 147ra111 (2012).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  9. 9.

    Abbott, N. J., Pizzo, M. E., Preston, J. E., Janigro, D. & Thorne, R. G. The role of brain barriers in fluid movement in the CNS: is there a ‘glymphatic’ system? Acta Neuropathol. 135, 387–407 (2018).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  10. 10.

    Asgari, M., de, Z. D. & Kurtcuoglu, V. Glymphatic solute transport does not require bulk flow. Sci. Rep. 6, 38635 (2016).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  11. 11.

    Faghih, M. M. & Sharp, M. K. Is bulk flow plausible in perivascular, paravascular and paravenous channels? Fluids Barriers CNS 15, 17 (2018).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  12. 12.

    Hladky, S. B. & Barrand, M. A. Mechanisms of fluid movement into, through and out of the brain: evaluation of the evidence. Fluids Barriers CNS 11, 26 (2014).

    PubMed  PubMed Central  Article  Google Scholar 

  13. 13.

    Hladky, S. B. & Barrand, M. A. Elimination of substances from the brain parenchyma: efflux via perivascular pathways and via the blood-brain barrier. Fluids Barriers CNS 15, 30 (2018).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  14. 14.

    Holter, K. E. et al. Interstitial solute transport in 3D reconstructed neuropil occurs by diffusion rather than bulk flow. Proc. Natl Acad. Sci. USA 114, 9894–9899 (2017).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  15. 15.

    Jin, B. J., Smith, A. J. & Verkman, A. S. Spatial model of convective solute transport in brain extracellular space does not support a “glymphatic” mechanism. J. Gen. Physiol. 148, 489–501 (2016).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  16. 16.

    Smith, A. J., Yao, X., Dix, J. A., Jin, B. J. & Verkman, A. S. Test of the ‘glymphatic’ hypothesis demonstrates diffusive and aquaporin-4-independent solute transport in rodent brain parenchyma. eLife 6, e27679 (2017).

    PubMed  PubMed Central  Article  Google Scholar 

  17. 17.

    Smith, A. J. & Verkman, A. S. The “glymphatic” mechanism for solute clearance in Alzheimer’s disease: game changer or unproven speculation? FASEB J. 32, 453–551 (2017).

    Google Scholar 

  18. 18.

    Spector, R., Robert, S. S. & Johanson, C. E. A balanced view of the cerebrospinal fluid composition and functions: focus on adult humans. Exp. Neurol. 273, 57–68 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  19. 19.

    Dandy, W. E. Experimental hydrocephalus. Ann. Surg. 70, 129–142 (1919). This study demonstrated the role of choroid plexus in CSF secretion.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  20. 20.

    Dietzel, I., Heinemann, U., Hofmeier, G. & Lux, H. D. Transient changes in the size of the extracellular space in the sensorimotor cortex of cats in relation to stimulus-induced changes in potassium concentration. Exp. Brain Res. 40, 432–439 (1980). This study was among the first to demonstrate the extracellular space shrinkage occurring with neuronal activity.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  21. 21.

    Eichling, J. O., Raichle, M. E., Grubb, R. L. Jr. & Ter-Pogossian, M. M. Evidence of the limitations of water as a freely diffusible tracer in brain of the rhesus monkey. Circ. Res. 35, 358–364 (1974).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  22. 22.

    Raichle, M. E. et al. Blood-brain barrier permeability of 11C-labeled alcohols and 15O-labeled water. Am. J. Physiol. 230, 543–552 (1976).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  23. 23.

    Fenstermacher, J. D. & Johnson, J. A. Filtration and reflection coefficients of the rabbit blood-brain barrier. Am. J. Physiol. 211, 341–346 (1966).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  24. 24.

    MacAulay, N., Hamann, S. & Zeuthen, T. in Physiology and Pathology of Chloride Transporters and Channels in the Nervous System (ed Alvarez-Leefmans, F. J. & Delpire, E.) Ch. 28, 547-568 (Academic Press, Elsevier, 2009).

  25. 25.

    Paulson, O. B., Hertz, M. M., Bolwig, T. G. & Lassen, N. A. Filtration and diffusion of water across the blood-brain barrier in man. Microvasc. Res. 13, 113–124 (1977).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  26. 26.

    Haj-Yasein, N. N. et al. Glial-conditional deletion of aquaporin-4 (Aqp4) reduces blood-brain water uptake and confers barrier function on perivascular astrocyte endfeet. Proc. Natl Acad. Sci. USA 108, 17815–17820 (2011). The study demonstrated the lack of AQP4 in brain endothelium.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  27. 27.

    Agre, P. Molecular physiology of water transport: aquaporin nomenclature workshop. Mammalian aquaporins. Biol. Cell 89, 255–257 (1997).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  28. 28.

    Wang, Y. & Tajkhorshid, E. Molecular mechanisms of conduction and selectivity in aquaporin water channels. J. Nutr. 137, 1509S–1515S (2007).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  29. 29.

    Ho, J. D. et al. Crystal structure of human aquaporin 4 at 1.8A and its mechanism of conductance. Proc. Natl Acad. Sci. USA 106, 7437–7442 (2009).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  30. 30.

    Litman, T., Sogaard, R. & Zeuthen, T. In: Aquaporins. Handbook of Experimental Pharmacology. 190 (ed Beitz, E.) 327-358 (Springer, 2009).

  31. 31.

    Zeuthen, T. & MacAulay, N. Passive water transport in biological pores. Int. Rev. Cytol. 215, 203–230 (2002).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  32. 32.

    Li, J. et al. Transient formation of water-conducting states in membrane transporters. Proc. Natl Acad. Sci. USA 110, 7696–7701 (2013).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  33. 33.

    MacAulay, N., Gether, U., Klaeke, D. A. & Zeuthen, T. Passive water and urea permeability of a human Na+-glutamate cotransporter expressed in Xenopus oocytes. J. Physiol. 542, 817–828 (2002).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  34. 34.

    Zeuthen, T. & MacAulay, N. Cotransporters as molecular water pumps. Int. Rev. Cytol. 215, 259–284 (2002).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  35. 35.

    Zeuthen, T. Water-transporting proteins. J. Membr. Biol. 234, 57–73 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  36. 36.

    Tait, M. J., Saadoun, S., Bell, B. A. & Papadopoulos, M. C. Water movements in the brain: role of aquaporins. Trends Neurosci. 31, 37–43 (2008).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  37. 37.

    Nielsen, S., Smith, B. L., Christensen, E. I. & Agre, P. Distribution of the aquaporin CHIP in secretory and resorptive epithelia and capillary endothelia. Proc. Natl Acad. Sci. USA 90, 7275–7279 (1993).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  38. 38.

    Speake, T., Freeman, L. J. & Brown, P. D. Expression of aquaporin 1 and aquaporin 4 water channels in rat choroid plexus. Biochim. Biophys. Acta 1609, 80–86 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  39. 39.

    Nielsen, S. et al. Specialized membrane domains for water transport in glial cells: high-resolution immunogold cytochemistry of aquaporin-4 in rat brain. J. Neurosci. 17, 171–180 (1997).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  40. 40.

    Li, Q. et al. Aquaporin 1 and the Na+/K+/2Cl cotransporter 1 are present in the leptomeningeal vasculature of the adult rodent central nervous system. Fluids Barriers CNS 17, 15 (2020).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  41. 41.

    Amiry-Moghaddam, M. & Ottersen, O. P. The molecular basis of water transport in the brain. Nat. Rev. Neurosci. 4, 991–1001 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  42. 42.

    Arcienega, I. I., Brunet, J. F., Bloch, J. & Badaut, J. Cell locations for AQP1, AQP4 and 9 in the non-human primate brain. Neuroscience 167, 1103–1114 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  43. 43.

    Zhang, Y. et al. An RNA-sequencing transcriptome and splicing database of glia, neurons, and vascular cells of the cerebral cortex. J. Neurosci. 34, 11929–11947 (2014).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  44. 44.

    Zhang, Y. et al. Purification and characterization of progenitor and mature human astrocytes reveals transcriptional and functional differences with mouse. Neuron 89, 37–53 (2016).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  45. 45.

    Misawa, T., Arima, K., Mizusawa, H. & Satoh, J. Close association of water channel AQP1 with amyloid-beta deposition in Alzheimer disease brains. Acta Neuropathol. 116, 247–260 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  46. 46.

    Nesic, O. et al. Aquaporin 1 - a novel player in spinal cord injury. J. Neurochem. 105, 628–640 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  47. 47.

    Satoh, J., Tabunoki, H., Yamamura, T., Arima, K. & Konno, H. Human astrocytes express aquaporin-1 and aquaporin-4 in vitro and in vivo. Neuropathology 27, 245–256 (2007).

    PubMed  Article  PubMed Central  Google Scholar 

  48. 48.

    Jung, J. S. et al. Molecular characterization of an aquaporin cDNA from brain: candidate osmoreceptor and regulator of water balance. PNAS 91, 13052–13056 (1994).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  49. 49.

    Hubbard, J. A., Hsu, M. S., Seldin, M. M. & Binder, D. K. Expression of the astrocyte water channel aquaporin-4 in the mouse brain. ASN Neuro https://doi.org/10.1177/1759091415605486 (2015).

    Article  PubMed  PubMed Central  Google Scholar 

  50. 50.

    Neely, J. D. et al. Syntrophin-dependent expression and localization of Aquaporin-4 water channel protein. Proc. Natl Acad. Sci. USA 98, 14108–14113 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  51. 51.

    Ma, T. et al. Generation and phenotype of a transgenic knockout mouse lacking the mercurial-insensitive water channel aquaporin-4. J. Clin. Invest 100, 957–962 (1997).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  52. 52.

    Amiry-Moghaddam, M. et al. Delayed K+ clearance associated with aquaporin-4 mislocalization: phenotypic defects in brains of alpha-syntrophin-null mice. Proc. Natl Acad. Sci. USA 100, 13615–13620 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  53. 53.

    Assentoft, M., Larsen, B. R. & MacAulay, N. Regulation and function of AQP4 in the central nervous system. Neurochem. Res. 40, 2615–2627 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  54. 54.

    Nagelhus, E. A., Mathiisen, T. M. & Ottersen, O. P. Aquaporin-4 in the central nervous system: cellular and subcellular distribution and coexpression with KIR4.1. Neuroscience 129, 905–913 (2004).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  55. 55.

    Papadopoulos, M. C. & Verkman, A. S. Aquaporin water channels in the nervous system. Nat. Rev. Neurosci. 14, 265–277 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  56. 56.

    Yao, X., Hrabetova, S., Nicholson, C. & Manley, G. T. Aquaporin-4-deficient mice have increased extracellular space without tortuosity change. J. Neurosci. 28, 5460–5464 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  57. 57.

    Eilert-Olsen, M. et al. Deletion of aquaporin-4 changes the perivascular glial protein scaffold without disrupting the brain endothelial barrier. Glia 60, 432–440 (2012).

    PubMed  Article  PubMed Central  Google Scholar 

  58. 58.

    Zeng, X. N. et al. Aquaporin-4 deficiency down-regulates glutamate uptake and GLT-1 expression in astrocytes. Mol. Cell Neurosci. 34, 34–39 (2007).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  59. 59.

    Fenton, R. A. et al. Differential water permeability and regulation of three aquaporin 4 isoforms. Cell Mol. Life Sci. 67, 829–840 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  60. 60.

    Assentoft, M. et al. Aquaporin 4 as a NH3 channel. J. Biol. Chem. 291, 19184–19195 (2016).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  61. 61.

    Moe, S. E. et al. New isoforms of rat Aquaporin-4. Genomics 91, 367–377 (2008).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  62. 62.

    Neely, J. D., Christensen, B. M., Nielsen, S. & Agre, P. Heterotetrameric composition of aquaporin-4 water channels. Biochemistry 38, 11156–11163 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  63. 63.

    Furman, C. S. et al. Aquaporin-4 square array assembly: opposing actions of M1 and M23 isoforms. Proc. Natl Acad. Sci. USA 100, 13609–13614 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  64. 64.

    Yang, B., Brown, D. & Verkman, A. S. The mercurial insensitive water channel (AQP-4) forms orthogonal arrays in stably transfected Chinese hamster ovary cells. J. Biol. Chem. 271, 4577–4580 (1996).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  65. 65.

    Landis, D. M. & Reese, T. S. Arrays of particles in freeze-fractured astrocytic membranes. J. Cell Biol. 60, 316–320 (1974).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  66. 66.

    Neuhaus, J. Orthogonal arrays of particles in astroglial cells: quantitative analysis of their density, size, and correlation with intramembranous particles. Glia 3, 241–251 (1990).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  67. 67.

    Solenov, E., Watanabe, H., Manley, G. T. & Verkman, A. S. Sevenfold-reduced osmotic water permeability in primary astrocyte cultures from AQP-4-deficient mice, measured by a fluorescence quenching method. Am. J. Physiol. Cell Physiol. 286, C426–C432 (2004). The study demonstrated the high astrocytic water permeability of AQP4-deficient astrocytes.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  68. 68.

    Gunnarson, E. et al. Identification of a molecular target for glutamate regulation of astrocyte water permeability. Glia 56, 587–596 (2008).

    PubMed  Article  PubMed Central  Google Scholar 

  69. 69.

    Song, Y. & Gunnarson, E. Potassium dependent regulation of astrocyte water permeability is mediated by cAMP signaling. PLoS ONE 7, e34936 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  70. 70.

    Zelenina, M., Zelenin, S., Bondar, A. A., Brismar, H. & Aperia, A. Water permeability of aquaporin-4 is decreased by protein kinase C and dopamine. Am. J. Physiol. Ren. Physiol. 283, F309–F318 (2002).

    CAS  Article  Google Scholar 

  71. 71.

    Assentoft, M. et al. Phosphorylation of rat aquaporin-4 at Ser(111) is not required for channel gating. Glia 61, 1101–1112 (2013).

    PubMed  Article  PubMed Central  Google Scholar 

  72. 72.

    Assentoft, M., Larsen, B. R., Olesen, E. T., Fenton, R. A. & MacAulay, N. AQP4 plasma membrane trafficking or channel gating is not significantly modulated by phosphorylation at COOH-terminal serine residues. Am. J. Physiol. Cell Physiol. 307, C957–C965 (2014).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  73. 73.

    Sachdeva, R. & Singh, B. Phosphorylation of Ser-180 of rat aquaporin-4 shows marginal affect on regulation of water permeability: molecular dynamics study. J. Biomol. Struct. Dyn. 32, 555–566 (2014).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  74. 74.

    Fischer, M. & Kaldenhoff, R. On the pH regulation of plant aquaporins. J. Biol. Chem. 283, 33889–33892 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  75. 75.

    Nemeth-Cahalan, K. L. & Hall, J. E. pH and calcium regulate the water permeability of aquaporin 0. J. Biol. Chem. 275, 6777–6782 (2000).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  76. 76.

    Zeuthen, T. & Klaerke, D. A. Transport of water and glycerol in aquaporin 3 is gated by H+. J. Biol. Chem. 274, 21631–21636 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  77. 77.

    Kaptan, S. et al. H95 is a pH-dependent gate in aquaporin 4. Structure 23, 2309–2318 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  78. 78.

    Alberga, D. et al. A new gating site in human aquaporin-4: insights from molecular dynamics simulations. Biochim. Biophys. Acta 1838, 3052–3060 (2014).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  79. 79.

    Kraig, R. P. & Chesler, M. Astrocytic acidosis in hyperglycemic and complete ischemia. J. Cereb. Blood Flow Metab. 10, 104–114 (1990).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  80. 80.

    MacAulay, N. & Zeuthen, T. Water transport between CNS compartments: contributions of aquaporins and cotransporters. Neuroscience 168, 941–956 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  81. 81.

    Zeuthen, T. et al. Water transport by the Na+/glucose cotransporter under isotonic conditions. Biol. Cell 89, 307–312 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  82. 82.

    Choe, S., Rosenberg, J. M., Abrahamson, J., Wright, E. M. & Grabe, M. Water permeation through the sodium-dependent galactose cotransporter vSGLT. Biophys. J. Biophys. Lett. 99, 56–58 (2010).

    Google Scholar 

  83. 83.

    Hamann, S., Kiilgaard, J. F., la Cour, M., Prause, J. U. & Zeuthen, T. Cotransport of H+, lactate, and H2O in porcine retinal pigment epithelial cells. Exp. Eye Res. 76, 493–504 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  84. 84.

    Hamann, S., Herrera-Perez, J. J., Zeuthen, T. & Alvarez-Leefmans, F. J. Cotransport of water by the Na+-K+-2Cl cotransporter NKCC1 in mammalian epithelial cells. J. Physiol. 588, 4089–4101 (2010).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  85. 85.

    MacAulay, N., Gether, U., Klaerke, D. A. & Zeuthen, T. Water transport by the human Na+-coupled glutamate cotransporter expressed in Xenopus oocytes. J. Physiol. 530, 367–378 (2001).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  86. 86.

    MacAulay, N., Zeuthen, T. & Gether, U. Conformational basis for the Li+-induced leak current in the rat gamma-aminobutyric acid (GABA) transporter-1. J. Physiol. 544, 447–458 (2002).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  87. 87.

    Steffensen, A. B. et al. Cotransporter-mediated water transport underlying cerebrospinal fluid formation. Nat. Commun. 9, 2167 (2018). This study demonstrated the role of NKCC1 in CSF secretion, showing that it functioned in a manner independent of the osmotic gradient.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  88. 88.

    Zeuthen, T. Cotransport of K+, Cl and H2O by membrane proteins from choroid plexus epithelium of Necturus maculosus. J. Physiol. 478, 203–219 (1994).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  89. 89.

    Kimelberg, H. K. Current concepts of brain edema. Review of laboratory investigations. J. Neurosurg. 83, 1051–1059 (1995).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  90. 90.

    Stokum, J. A., Gerzanich, V. & Simard, J. M. Molecular pathophysiology of cerebral edema. J. Cereb. Blood Flow Metab. 36, 513–538 (2016).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  91. 91.

    Davalos, A., Shuaib, A. & Wahlgren, N. G. Neurotransmitters and pathophysiology of stroke: evidence for the release of glutamate and other transmitters/mediators in animals and humans. J. Stroke Cerebrovasc. Dis. 9, 2–8 (2000).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  92. 92.

    Hossmann, K. A., Sakaki, S. & Zimmerman, V. Cation activities in reversible ischemia of the cat brain. Stroke 8, 77–81 (1977).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  93. 93.

    Walz, W. & Mukerji, S. KCl movements during potassium-induced cytotoxic swelling of cultured astrocytes. Exp. Neurol. 99, 17–29 (1988).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  94. 94.

    Benfenati, V. et al. An aquaporin-4/transient receptor potential vanilloid 4 (AQP4/TRPV4) complex is essential for cell-volume control in astrocytes. Proc. Natl Acad. Sci. USA 108, 2563–2568 (2011).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  95. 95.

    Mola, M. G. et al. The speed of swelling kinetics modulates cell volume regulation and calcium signaling in astrocytes: a different point of view on the role of aquaporins. Glia 64, 139–154 (2016).

    PubMed  Article  PubMed Central  Google Scholar 

  96. 96.

    Jo, A. O. et al. TRPV4 and AQP4 channels synergistically regulate cell volume and calcium homeostasis in retinal muller glia. J. Neurosci. 35, 13525–13537 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  97. 97.

    Toft-Bertelsen, T. L., Krizaj, D. & MacAulay, N. When size matters: transient receptor potential vanilloid 4 channel as a volume-sensor rather than an osmo-sensor. J. Physiol. 595, 3287–3302 (2017).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  98. 98.

    Toft-Bertelsen, T. L., Larsen, B. R. & MacAulay, N. Sensing and regulation of cell volume - we know so much and yet understand so little: TRPV4 as a sensor of volume changes but possibly without a volume-regulatory role? Channels 12, 100–108 (2018).

    PubMed  PubMed Central  Article  Google Scholar 

  99. 99.

    Stokum, J. A. et al. SUR1-TRPM4 and AQP4 form a heteromultimeric complex that amplifies ion/water osmotic coupling and drives astrocyte swelling. Glia 66, 108–125 (2018).

    PubMed  Article  PubMed Central  Google Scholar 

  100. 100.

    Rakers, C., Schmid, M. & Petzold, G. C. TRPV4 channels contribute to calcium transients in astrocytes and neurons during peri-infarct depolarizations in a stroke model. Glia 65, 1550–1561 (2017).

    PubMed  Article  PubMed Central  Google Scholar 

  101. 101.

    Rosic, B. et al. Aquaporin-4-independent volume dynamics of astroglial endfeet during cortical spreading depression. Glia 67, 1113–1121 (2019). This study demonstrated that SD-induced glia cell swelling occurred independently of AQP4.

    PubMed  PubMed Central  Article  Google Scholar 

  102. 102.

    Ballanyi, K., Grafe, P. & Ten Bruggencate, G. Ion activities and potassium uptake mechanisms of glial cells in guinea-pig olfactory cortex slices. J. Physiol. 382, 159–174 (1987).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  103. 103.

    Grafe, P. & Ballanyi, K. Cellular mechanisms of potassium homeostasis in the mammalian nervous system. Can. J. Physiol. Pharmacol. 65, 1038–1042 (1987).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  104. 104.

    Coles, J. A. & Schneider-Picard, G. Increase in glial intracellular K+ in drone retina caused by photostimulation but not mediated by an increase in extracellular K+. Glia 2, 213–222 (1989).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  105. 105.

    Larsen, B. R., Stoica, A. & MacAulay, N. Managing brain extracellular K+ during neuronal activity: the physiological role of the Na+/K+-ATPase subunit isoforms. Front. Physiol. 7, 141 (2016).

    PubMed  PubMed Central  Article  Google Scholar 

  106. 106.

    MacAulay, N. Molecular mechanisms of K+ clearance and extracellular space shrinkage-glia cells as the stars. Glia https://doi.org/10.1002/glia.23824 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  107. 107.

    Hochman, D. W., Baraban, S. C., Owens, J. W. & Schwartzkroin, P. A. Dissociation of synchronization and excitability in furosemide blockade of epileptiform activity. Science 270, 99–102 (1995).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  108. 108.

    Larsen, B. R. et al. Contributions of the Na+ /K+-ATPase, NKCC1, and Kir4.1 to hippocampal K+ clearance and volume responses. Glia 62, 608–622 (2014). This study demonstrated that glial K+-transporting mechanisms do not contribute to extracellular space shrinkage.

    PubMed  PubMed Central  Article  Google Scholar 

  109. 109.

    MacVicar, B. A. & Hochman, D. Imaging of synaptically evoked intrinsic optical signals in hippocampal slices. J. Neurosci. 11, 1458–1469 (1991).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  110. 110.

    MacVicar, B. A., Feighan, D., Brown, A. & Ransom, B. Intrinsic optical signals in the rat optic nerve: role for K+ uptake via NKCC1 and swelling of astrocytes. Glia 37, 114–123 (2002).

    PubMed  Article  PubMed Central  Google Scholar 

  111. 111.

    Orkand, R. K., Dietzel, I. & Coles, J. A. Light-induced changes in extracellular volume in the retina of the drone, Apis mellifera. Neurosci. Lett. 45, 273–278 (1984).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  112. 112.

    Pal, I., Nyitrai, G., Kardos, J. & Heja, L. Neuronal and astroglial correlates underlying spatiotemporal intrinsic optical signal in the rat hippocampal slice. PLoS ONE 8, e57694 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  113. 113.

    Ransom, B. R., Yamate, C. L. & Connors, B. W. Activity-dependent shrinkage of extracellular space in rat optic nerve: a developmental study. J. Neurosci. 5, 532–535 (1985). This study demonstrated that glial maturation is required for activity-evoked extracellular space shrinkage.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  114. 114.

    Florence, C. M., Baillie, L. D. & Mulligan, S. J. Dynamic volume changes in astrocytes are an intrinsic phenomenon mediated by bicarbonate ion flux. PLoS ONE 7, e51124 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  115. 115.

    Larsen, B. R., Stoica, A. & MacAulay, N. Developmental maturation of activity-induced K+ and pH transients and the associated extracellular space dynamics in the rat hippocampus. J. Physiol. 597, 583–597 (2019).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  116. 116.

    Hertz, L. et al. Astrocytic and neuronal accumulation of elevated extracellular K+ with a 2/3K+/Na+ flux ratio-consequences for energy metabolism, osmolarity and higher brain function. Front. Comput. Neurosci. 7, 114 (2013).

    PubMed  PubMed Central  Article  Google Scholar 

  117. 117.

    Kofuji, P. & Newman, E. A. Potassium buffering in the central nervous system. Neuroscience 129, 1045–1056 (2004).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  118. 118.

    MacAulay, N. & Zeuthen, T. Glial K+ clearance and cell swelling: key roles for cotransporters and pumps. Neurochem. Res. 37, 2299–2309 (2012).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  119. 119.

    Nagelhus, E. A. et al. Immunogold evidence suggests that coupling of K+ siphoning and water transport in rat retinal Muller cells is mediated by a co-enrichment of Kir4.1 and AQP4 in specific membrane domains. Glia 26, 47–54 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  120. 120.

    Nagelhus, E. A. & Ottersen, O. P. Physiological roles of aquaporin-4 in brain. Physiol. Rev. 93, 1543–1562 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  121. 121.

    Haj-Yasein, N. N. et al. Aquaporin-4 regulates extracellular space volume dynamics during high-frequency synaptic stimulation: a gene deletion study in mouse hippocampus. Glia 60, 867–874 (2012).

    PubMed  Article  PubMed Central  Google Scholar 

  122. 122.

    Toft-Bertelsen, T. L. et al. Clearance of activity-evoked K+ transients and associated glia cell swelling occur independently of AQP4: A study with an isoform-selective AQP4 inhibitor. Glia 69, 28–41 (2020). This study demonstrated robust activity-evoked extracellular space shrinkage in the absence of AQP4.

    PubMed  Article  PubMed Central  Google Scholar 

  123. 123.

    Haj-Yasein, N. N. et al. Evidence that compromised K+ spatial buffering contributes to the epileptogenic effect of mutations in the human kir4.1 gene (KCNJ10). Glia 59, 1635–1642 (2011).

    PubMed  Article  PubMed Central  Google Scholar 

  124. 124.

    Larsen, B. R. & MacAulay, N. Kir4.1-mediated spatial buffering of K+: experimental challenges in determination of its temporal and quantitative contribution to K+ clearance in the brain. Channels 8, 544–550 (2014).

    PubMed  PubMed Central  Article  Google Scholar 

  125. 125.

    Orkand, R. K., Nicholls, J. G. & Kuffler, S. W. Effect of nerve impulses on the membrane potential of glial cells in the central nervous system of amphibia. J. Neurophysiol. 29, 788–806 (1966).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  126. 126.

    Ruiz-Ederra, J., Zhang, H. & Verkman, A. S. Evidence against functional interaction between aquaporin-4 water channels and Kir4.1 potassium channels in retinal Muller cells. J. Biol. Chem. 282, 21866–21872 (2007).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  127. 127.

    Binder, D. K. et al. Increased seizure duration and slowed potassium kinetics in mice lacking aquaporin-4 water channels. Glia 53, 631–636 (2006).

    PubMed  Article  PubMed Central  Google Scholar 

  128. 128.

    Haj-Yasein, N. N. et al. Deletion of aquaporin-4 increases extracellular K+ concentration during synaptic stimulation in mouse hippocampus. Brain Struct. Funct. 220, 2469–2474 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  129. 129.

    Strohschein, S. et al. Impact of aquaporin-4 channels on K+ buffering and gap junction coupling in the hippocampus. Glia 59, 973–980 (2011).

    PubMed  Article  PubMed Central  Google Scholar 

  130. 130.

    Jin, B. J., Zhang, H., Binder, D. K. & Verkman, A. S. Aquaporin-4-dependent K+ and water transport modeled in brain extracellular space following neuroexcitation. J. Gen. Physiol. 141, 119–132 (2013).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  131. 131.

    Binder, D. K., Yao, X., Verkman, A. S. & Manley, G. T. Increased seizure duration in mice lacking aquaporin-4 water channels. Acta Neurochir. Suppl. 96, 389–392 (2006).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  132. 132.

    D’Ambrosio, R., Gordon, D. S. & Winn, H. R. Differential role of KIR channel and Na+/K+-pump in the regulation of extracellular K+ in rat hippocampus. J. Neurophysiol. 87, 87–102 (2002).

    PubMed  Article  PubMed Central  Google Scholar 

  133. 133.

    Bourke, R. S. & Nelson, K. M. Further studies on the K+-dependent swelling of primate cerebral cortex in vivo: the enzymatic basis of the K+-dependent transport of chloride. J. Neurochem. 19, 663–685 (1972).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  134. 134.

    Larsen, B. R. & MacAulay, N. Activity-dependent astrocyte swelling is mediated by pH-regulating mechanisms. Glia 65, 1668–1681 (2017). This study demonstrated the importance of pH-regulating transporters in activity-evoked extracellular space shrinkage.

    PubMed  Article  PubMed Central  Google Scholar 

  135. 135.

    Holthoff, K. & Witte, O. W. Intrinsic optical signals in rat neocortical slices measured with near-infrared dark-field microscopy reveal changes in extracellular space. J. Neurosci. 16, 2740–2749 (1996).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  136. 136.

    Su, G., Kintner, D. B. & Sun, D. Contribution of Na+-K+-Cl cotransporter to high-[K+]o- induced swelling and EAA release in astrocytes. Am. J. Physiol. Cell Physiol. 282, C1136–C1146 (2002).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  137. 137.

    Walz, W. & Hinks, E. C. Carrier-mediated KCl accumulation accompanied by water movements is involved in the control of physiological K+ levels by astrocytes. Brain Res. 343, 44–51 (1985).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  138. 138.

    Walz, W. Role of Na/K/Cl cotransport in astrocytes. Can. J. Physiol. Pharmacol. 70 (Suppl.), S260–S262 (1992).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  139. 139.

    Zeuthen, T. & MacAulay, N. Cotransport of water by Na+-K+-2Cl cotransporters expressed in Xenopus oocytes: NKCC1 versus NKCC2. J. Physiol. 590, 1139–1154 (2012). This study demonstrated the ability of NKCC1 to cotransport water.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  140. 140.

    Plotkin, M. D. et al. Expression of the Na+-K+-2Cl cotransporter BSC2 in the nervous system. Am. J. Physiol. 272, C173–C183 (1997). This study demonstrated the lack of NKCC1 expression in glial cells and endothelium and its abundance in the choroid plexus.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  141. 141.

    Raat, N. J., Delpire, E., Van Os, C. H. & Bindels, R. J. Culturing induced expression of basolateral Na+-K+-2Cl cotransporter BSC2 in proximal tubule, aortic endothelium, and vascular smooth muscle. Pflug. Arch. 431, 458–460 (1996).

    CAS  Google Scholar 

  142. 142.

    Danbolt, N. C. Glutamate uptake. Prog. Neurobiol. 65, 1–105 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  143. 143.

    Schools, G. P. & Kimelberg, H. K. mGluR3 and mGluR5 are the predominant metabotropic glutamate receptor mRNAs expressed in hippocampal astrocytes acutely isolated from young rats. J. Neurosci. Res. 58, 533–543 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  144. 144.

    Hansson, E. Metabotropic glutamate receptor activation induces astroglial swelling. J. Biol. Chem. 269, 21955–21961 (1994).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  145. 145.

    Izumi, Y., Kirby, C. O., Benz, A. M., Olney, J. W. & Zorumski, C. F. Muller cell swelling, glutamate uptake, and excitotoxic neurodegeneration in the isolated rat retina. Glia 25, 379–389 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  146. 146.

    Schneider, G. H., Baethmann, A. & Kempski, O. Mechanisms of glial swelling induced by glutamate. Can. J. Physiol. Pharmacol. 70 (Suppl.), S334–S343 (1992).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  147. 147.

    Makani, S. & Chesler, M. Rapid rise of extracellular pH evoked by neural activity is generated by the plasma membrane calcium ATPase. J. Neurophysiol. 103, 667–676 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  148. 148.

    Voipio, J. & Kaila, K. Interstitial PCO2 and pH in rat hippocampal slices measured by means of a novel fast CO2/H+-sensitive microelectrode based on a PVC-gelled membrane. Pflug. Arch. 423, 193–201 (1993).

    CAS  Article  Google Scholar 

  149. 149.

    Chesler, M. Regulation and modulation of pH in the brain. Physiol. Rev. 83, 1183–1221 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  150. 150.

    Theparambil, S. M., Ruminot, I., Schneider, H. P., Shull, G. E. & Deitmer, J. W. The electrogenic sodium bicarbonate cotransporter NBCe1 is a high-affinity bicarbonate carrier in cortical astrocytes. J. Neurosci. 34, 1148–1157 (2014).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  151. 151.

    Deitmer, J. W. & Szatkowski, M. Membrane potential dependence of intracellular pH regulation by identified glial cells in the leech central nervous system. J. Physiol. 421, 617–631 (1990).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  152. 152.

    Pappas, C. A. & Ransom, B. R. Depolarization-induced alkalinization (DIA) in rat hippocampal astrocytes. J. Neurophysiol. 72, 2816–2826 (1994).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  153. 153.

    Theparambil, S. M., Naoshin, Z., Thyssen, A. & Deitmer, J. W. Reversed electrogenic sodium bicarbonate cotransporter 1 is the major acid loader during recovery from cytosolic alkalosis in mouse cortical astrocytes. J. Physiol. 593, 3533–3547 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  154. 154.

    Barros, L. F. Metabolic signaling by lactate in the brain. Trends Neurosci. 36, 396–404 (2013).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  155. 155.

    Mangia, S. et al. The aerobic brain: lactate decrease at the onset of neural activity. Neuroscience 118, 7–10 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  156. 156.

    Bergersen, L. et al. A novel postsynaptic density protein: the monocarboxylate transporter MCT2 is co-localized with delta-glutamate receptors in postsynaptic densities of parallel fiber-Purkinje cell synapses. Exp. Brain Res. 136, 523–534 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  157. 157.

    Pierre, K., Pellerin, L., Debernardi, R., Riederer, B. M. & Magistretti, P. J. Cell-specific localization of monocarboxylate transporters, MCT1 and MCT2, in the adult mouse brain revealed by double immunohistochemical labeling and confocal microscopy. Neuroscience 100, 617–627 (2000).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  158. 158.

    Rafiki, A., Boulland, J. L., Halestrap, A. P., Ottersen, O. P. & Bergersen, L. Highly differential expression of the monocarboxylate transporters MCT2 and MCT4 in the developing rat brain. Neuroscience 122, 677–688 (2003).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  159. 159.

    Zeuthen, T., Hamann, S. & la Cour, M. Cotransport of H+, lactate and H2O by membrane proteins in retinal pigment epithelium of bullfrog. J. Physiol. 497, 3–17 (1996).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  160. 160.

    Andrew, R. D., Labron, M. W., Boehnke, S. E., Carnduff, L. & Kirov, S. A. Physiological evidence that pyramidal neurons lack functional water channels. Cereb. Cortex 17, 787–802 (2007). This study demonstrated the excessively low neuronal osmotic water permeability.

    PubMed  Article  PubMed Central  Google Scholar 

  161. 161.

    Risher, W. C., Andrew, R. D. & Kirov, S. A. Real-time passive volume responses of astrocytes to acute osmotic and ischemic stress in cortical slices and in vivo revealed by two-photon microscopy. Glia 57, 207–221 (2009).

    PubMed  PubMed Central  Article  Google Scholar 

  162. 162.

    Steffensen, A. B., Sword, J., Croom, D., Kirov, S. A. & MacAulay, N. Chloride cotransporters as a molecular mechanism underlying spreading depolarization-induced dendritic beading. J. Neurosci. 35, 12172–12187 (2015). This study demonstrated the role of cotransporters in SD-induced dendritic beading.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  163. 163.

    Rash, J. E., Yasumura, T., Hudson, C. S., Agre, P. & Nielsen, S. Direct immunogold labeling of aquaporin-4 in square arrays of astrocyte and ependymocyte plasma membranes in rat brain and spinal cord. Proc. Natl Acad. Sci. USA 95, 11981–11986 (1998).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  164. 164.

    Aitken, P. G. et al. Volume changes induced by osmotic stress in freshly isolated rat hippocampal neurons. Pflug. Arch. 436, 991–998 (1998).

    CAS  Article  Google Scholar 

  165. 165.

    Pasantes-Morales, H., Maar, T. E. & Moran, J. Cell volume regulation in cultured cerebellar granule neurons. J. Neurosci. Res. 34, 219–224 (1993).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  166. 166.

    Risher, W. C., Croom, D. & Kirov, S. A. Persistent astroglial swelling accompanies rapid reversible dendritic injury during stroke-induced spreading depolarizations. Glia 60, 1709–1720 (2012).

    PubMed  PubMed Central  Article  Google Scholar 

  167. 167.

    Takano, T. et al. Cortical spreading depression causes and coincides with tissue hypoxia. Nat. Neurosci. 10, 754–762 (2007).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  168. 168.

    Dreier, J. P. & Reiffurth, C. The stroke-migraine depolarization continuum. Neuron 86, 902–922 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  169. 169.

    Hartings, J. A. et al. Spreading depolarisations and outcome after traumatic brain injury: a prospective observational study. Lancet Neurol. 10, 1058–1064 (2011).

    PubMed  Article  PubMed Central  Google Scholar 

  170. 170.

    Oliveira-Ferreira, A. I. et al. Experimental and preliminary clinical evidence of an ischemic zone with prolonged negative DC shifts surrounded by a normally perfused tissue belt with persistent electrocorticographic depression. J. Cereb. Blood Flow Metab. 30, 1504–1519 (2010).

    PubMed  PubMed Central  Article  Google Scholar 

  171. 171.

    Dreier, J. P. et al. Delayed ischaemic neurological deficits after subarachnoid haemorrhage are associated with clusters of spreading depolarizations. Brain 129, 3224–3237 (2006).

    PubMed  Article  PubMed Central  Google Scholar 

  172. 172.

    Lauritzen, M. et al. Clinical relevance of cortical spreading depression in neurological disorders: migraine, malignant stroke, subarachnoid and intracranial hemorrhage, and traumatic brain injury. J. Cereb. Blood Flow Metab. 31, 17–35 (2011).

    PubMed  Article  PubMed Central  Google Scholar 

  173. 173.

    Hartings, J. A. et al. Spreading depolarizations have prolonged direct current shifts and are associated with poor outcome in brain trauma. Brain 134, 1529–1540 (2011).

    PubMed  Article  PubMed Central  Google Scholar 

  174. 174.

    Dreier, J. P. The role of spreading depression, spreading depolarization and spreading ischemia in neurological disease. Nat. Med. 17, 439–447 (2011).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  175. 175.

    Leao, A. A. Spreading depression of activity in the cerebral cortex. J. Neurophysiol. 7, 359–390 (1944).

    Article  Google Scholar 

  176. 176.

    Hansen, A. J. & Zeuthen, T. Extracellular ion concentrations during spreading depression and ischemia in the rat brain cortex. Acta Physiol. Scand. 113, 437–445 (1981).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  177. 177.

    Kraig, R. P. & Nicholson, C. Extracellular ionic variations during spreading depression. Neuroscience 3, 1045–1059 (1978).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  178. 178.

    Somjen, G. G. Mechanisms of spreading depression and hypoxic spreading depression-like depolarization. Physiol. Rev. 81, 1065–1096 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  179. 179.

    Snow, R. W., Taylor, C. P. & Dudek, F. E. Electrophysiological and optical changes in slices of rat hippocampus during spreading depression. J. Neurophysiol. 50, 561–572 (1983).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  180. 180.

    Muller, M. & Somjen, G. G. Intrinsic optical signals in rat hippocampal slices during hypoxia-induced spreading depression-like depolarization. J. Neurophysiol. 82, 1818–1831 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  181. 181.

    Zhou, N., Gordon, G. R., Feighan, D. & MacVicar, B. A. Transient swelling, acidification, and mitochondrial depolarization occurs in neurons but not astrocytes during spreading depression. Cereb. Cortex 20, 2614–2624 (2010).

    PubMed  Article  PubMed Central  Google Scholar 

  182. 182.

    Risher, W. C., Ard, D., Yuan, J. & Kirov, S. A. Recurrent spontaneous spreading depolarizations facilitate acute dendritic injury in the ischemic penumbra. J. Neurosci. 30, 9859–9868 (2010). This study demonstrated the appearance of dendritic beading during ischaemia.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  183. 183.

    Rungta, R. L. et al. The cellular mechanisms of neuronal swelling underlying cytotoxic edema. Cell 161, 610–621 (2015).

    CAS  Article  Google Scholar 

  184. 184.

    Hoskison, M. M., Yanagawa, Y., Obata, K. & Shuttleworth, C. W. Calcium-dependent NMDA-induced dendritic injury and MAP2 loss in acute hippocampal slices. Neuroscience 145, 66–79 (2007).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  185. 185.

    Gisselsson, L. L., Matus, A. & Wieloch, T. Actin redistribution underlies the sparing effect of mild hypothermia on dendritic spine morphology after in vitro ischemia. J. Cereb. Blood Flow Metab. 25, 1346–1355 (2005).

    PubMed  Article  PubMed Central  Google Scholar 

  186. 186.

    Hoskison, M. M. & Shuttleworth, C. W. Microtubule disruption, not calpain-dependent loss of MAP2, contributes to enduring NMDA-induced dendritic dysfunction in acute hippocampal slices. Exp. Neurol. 202, 302–312 (2006).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  187. 187.

    Sword, J., Croom, D., Wang, P. L., Thompson, R. J. & Kirov, S. A. Neuronal pannexin-1 channels are not molecular routes of water influx during spreading depolarization-induced dendritic beading. J. Cereb. Blood Flow Metab. 37, 1626–1633 (2017).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  188. 188.

    Van, H. A. & Schade, J. P. Chloride movements in cerebral cortex after circulatory arrest and during spreading depression. J. Cell Comp. Physiol. 54, 65–84 (1959).

    Article  Google Scholar 

  189. 189.

    Muller, M. Effects of chloride transport inhibition and chloride substitution on neuron function and on hypoxic spreading-depression-like depolarization in rat hippocampal slices. Neuroscience 97, 33–45 (2000).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  190. 190.

    Kopito, R. R. et al. Regulation of intracellular pH by a neuronal homolog of the erythrocyte anion exchanger. Cell 59, 927–937 (1989).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  191. 191.

    Payne, J. A. Functional characterization of the neuronal-specific K-Cl cotransporter: implications for [K+]o regulation. Am. J. Physiol. 273, C1516–C1525 (1997).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  192. 192.

    Pierre, K., Magistretti, P. J. & Pellerin, L. MCT2 is a major neuronal monocarboxylate transporter in the adult mouse brain. J. Cereb. Blood Flow Metab. 22, 586–595 (2002).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  193. 193.

    Heisey, S. R., Held, D. & Pappenheimer, J. R. Bulk flow and diffusion in the cerebrospinal fluid system of the goat. Am. J. Physiol. 203, 775–781 (1962). This study was the first to demonstrate the ability of CSF secretion against an osmotic gradient.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  194. 194.

    Pollay, M. Formation of cerebrospinal fluid. Relation of studies of isolated choroid plexus to the standing gradient hypothesis. J. Neurosurg. 42, 665–673 (1975).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  195. 195.

    Segal, M. B. & Pollay, M. The secretion of cerebrospinal fluid. Exp. Eye Res. 25, 127–148 (1977).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  196. 196.

    Damkier, H. H., Brown, P. D. & Praetorius, J. Cerebrospinal fluid secretion by the choroid plexus. Physiol. Rev. 93, 1847–1892 (2013).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  197. 197.

    Hochwald, G. M., Wald, A., DiMattio, J. & Malhan, C. The effects of serum osmolarity on cerebrospinal fluid volume flow. Life Sci. 15, 1309–1316 (1974).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  198. 198.

    Javaheri, S. & Wagner, K. R. Bumetanide decreases canine cerebrospinal fluid production. In vivo evidence for NaCl cotransport in the central nervous system. J. Clin. Invest. 92, 2257–2261 (1993).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  199. 199.

    Nilsson, C. et al. Circadian variation in human cerebrospinal fluid production measured by magnetic resonance imaging. Am. J. Physiol. 262, R20–R24 (1992).

    CAS  PubMed  PubMed Central  Google Scholar 

  200. 200.

    Pullen, R. G., DePasquale, M. & Cserr, H. F. Bulk flow of cerebrospinal fluid into brain in response to acute hyperosmolality. Am. J. Physiol. 253, F538–F545 (1987).

    CAS  PubMed  PubMed Central  Google Scholar 

  201. 201.

    Rubin, R. C., Henderson, E. S., Ommaya, A. K., Walker, M. D. & Rall, D. P. The production of cerebrospinal fluid in man and its modification by acetazolamide. J. Neurosurg. 25, 430–436 (1966).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  202. 202.

    Damkier, H. H., Brown, P. D. & Praetorius, J. Epithelial pathways in choroid plexus electrolyte transport. Physiology 25, 239–249 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  203. 203.

    de Rougemont, J., Ames, A. III, Nesbett, F. B. & Hofmann, H. F. Fluid formed by choroid plexus; a technique for its collection and a comparison of its electrolyte composition with serum and cisternal fluids. J. Neurophysiol. 23, 485–495 (1960). This study demonstrated that newly formed CSF and bulk CSF are similar in electrolyte composition and osmolarity.

    PubMed  Article  PubMed Central  Google Scholar 

  204. 204.

    Welch, K. Secretion of cerebrospinal fluid by choroid plexus of the rabbit. Am. J. Physiol. 205, 617–624 (1963).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  205. 205.

    Davson, H. & Segal, M. B. The effects of some inhibitors and accelerators of sodium transport on the turnover of 22Na in the cerebrospinal fluid and the brain. J. Physiol. 209, 131–153 (1970).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  206. 206.

    Smith, Q. R., Johanson, C. E. & Woodbury, D. M. Uptake of 36Cl and 22Na by the brain-cerebrospinal fluid system: comparison of the permeability of the blood-brain and blood-cerebrospinal fluid barriers. J. Neurochem. 37, 117–124 (1981).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  207. 207.

    Smith, Q. R. & Rapoport, S. I. Cerebrovascular permeability coefficients to sodium, potassium, and chloride. J. Neurochem. 46, 1732–1742 (1986).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  208. 208.

    Davson, H. A comparative study of the aqueous humour and cerebrospinal fluid in the rabbit. J. Physiol. 129, 111–133 (1955).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  209. 209.

    Ames, A. III, Higashi, K. & NESBETT, F. B. Effects of PCO2 acetazolamide and ouabain on volume and composition of choroid-plexus fluid. J. Physiol. 181, 516–524 (1965).

    PubMed  PubMed Central  Article  Google Scholar 

  210. 210.

    Knuckey, N. W., Fowler, A. G., Johanson, C. E., Nashold, J. R. & Epstein, M. H. Cisterna magna microdialysis of 22Na to evaluate ion transport and cerebrospinal fluid dynamics. J. Neurosurg. 74, 965–971 (1991).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  211. 211.

    Pollay, M. et al. Choroid plexus Na+/K+-activated adenosine triphosphatase and cerebrospinal fluid formation. Neurosurgery 17, 768–772 (1985).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  212. 212.

    DePasquale, M., Patlak, C. S. & Cserr, H. F. Brain ion and volume regulation during acute hypernatremia in Brattleboro rats. Am. J. Physiol. 256, F1059–F1066 (1989).

    CAS  PubMed  PubMed Central  Google Scholar 

  213. 213.

    Pollay, M. & Curl, F. Secretion of cerebrospinal fluid by the ventricular ependyma of the rabbit. Am. J. Physiol. 213, 1031–1038 (1967).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  214. 214.

    Bradbury, M. W. & Kleeman, C. R. The effect of chronic osmotic disturbance on the concentrations of cations in cerebrospinal fluid. J. Physiol. 204, 181–193 (1969).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  215. 215.

    Wald, A., Hochwald, G. M. & Malhan, C. The effects of ventricular fluid osmolality on bulk flow of nascent fluid into the cerebral ventricles of cats. Exp. Brain Res. 25, 157–167 (1976).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  216. 216.

    Hendry, E. B. The osmotic pressure and chemical composition of human body fluids. Clin. Chem. 8, 246–265 (1962).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  217. 217.

    Welch, K., Sadler, K. & Gold, G. Volume flow across choroidal ependyma of the rabbit. Am. J. Physiol. 210, 232–236 (1966).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  218. 218.

    Zeuthen, T. Water permeability of ventricular cell membrane in choroid plexus epithelium from Necturus maculosus. J. Physiol. 444, 133–151 (1991). This study demonstrated the lack of unstirred layers on the luminal side of the choroid plexus.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  219. 219.

    Zeuthen, T. & Steffensen, A. B. in Role of the Choroid Plexus in Health and Disease (eds Praetorius, J., Blazer-Yost, B. & Damkier, H.) (Springer, 2020).

  220. 220.

    Curl, F. D. & Pollay, M. Transport of water and electrolytes between brain and ventricular fluid in the rabbit. Exp. Neurol. 20, 558–574 (1968).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  221. 221.

    Hochwald, G. M., Wald, A. & Malhan, C. The sink action of cerebrospinal fluid volume flow. Effect on brain water content. Arch. Neurol. 33, 339–344 (1976).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  222. 222.

    Sahar, A. & Tsipstein, E. Effects of mannitol and furosemide on the rate of formation of cerebrospinal fluid. Exp. Neurol. 60, 584–591 (1978).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  223. 223.

    Oshio, K., Watanabe, H., Song, Y., Verkman, A. S. & Manley, G. T. Reduced cerebrospinal fluid production and intracranial pressure in mice lacking choroid plexus water channel Aquaporin-1. FASEB J. 19, 76–78 (2005). This study found that Aqp1-/- mice exhibited a 20% reduction in CSF secretion.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  224. 224.

    Praetorius, J. & Nielsen, S. Distribution of sodium transporters and aquaporin-1 in the human choroid plexus. Am. J. Physiol. Cell Physiol. 291, C59–C67 (2006).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  225. 225.

    Chretien, S. & Catron, J. P. A single mutation inside the NPA motif of aquaporin-1 found in a Colton-null phenotype. Blood 93, 4021–4023 (1999).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  226. 226.

    Preston, G. M., Smith, B. L., Zeidel, M. L., Moulds, J. J. & Agre, P. Mutations in aquaporin-1 in phenotypically normal humans without functional CHIP water channels. Science 265, 1585–1587 (1994). This study demonstrated that humans with no AQP1 expression have no neurological deficits.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  227. 227.

    Ma, T. et al. Severely impaired urinary concentrating ability in transgenic mice lacking aquaporin-1 water channels. J. Biol. Chem. 273, 4296–4299 (1998).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  228. 228.

    Quinton, P. M., Wright, E. M. & Tormey, J. M. Localization of sodium pumps in the choroid plexus epithelium. J. Cell Biol. 58, 724–730 (1973).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  229. 229.

    Bradbury, M. W. & Kleeman, C. R. Stability of the potassium content of cerebrospinal fluid and brain. Am. J. Physiol. 213, 519–528 (1967).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  230. 230.

    Smith, Q. R. & Johanson, C. E. Effect of ouabain and potassium on ion concentrations in the choroidal epithelium. Am. J. Physiol. 238, F399–F406 (1980).

    CAS  PubMed  PubMed Central  Google Scholar 

  231. 231.

    Lun, M. P. et al. Spatially heterogeneous choroid plexus transcriptomes encode positional identity and contribute to regional CSF production. J. Neurosci. 35, 4903–4916 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  232. 232.

    Vates, T. S. Jr., Bonting, S. L. & Oppelt, W. W. Na-K activated adenosine triphosphatase formation of cerebrospinal fluid in the cat. Am. J. Physiol. 206, 1165–1172 (1964).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  233. 233.

    Deng, Q. S. & Johanson, C. E. Cyclic AMP alteration of chloride transport into the choroid plexus-cerebrospinal fluid system. Neurosci. Lett. 143, 146–150 (1992).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  234. 234.

    Lindsey, A. E. et al. Functional expression and subcellular localization of an anion exchanger cloned from choroid plexus. Proc. Natl Acad. Sci. USA 87, 5278–5282 (1990).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  235. 235.

    Praetorius, J., Nejsum, L. N. & Nielsen, S. A SCL4A10 gene product maps selectively to the basolateral plasma membrane of choroid plexus epithelial cells. Am. J. Physiol. Cell Physiol. 286, C601–C610 (2004).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  236. 236.

    Praetorius, J. & Damkier, H. H. Transport across the choroid plexus epithelium. Am. J. Physiol. Cell Physiol. 312, C673–C686 (2017).

    PubMed  Article  PubMed Central  Google Scholar 

  237. 237.

    Deng, Q. S. & Johanson, C. E. Stilbenes inhibit exchange of chloride between blood, choroid plexus and cerebrospinal fluid. Brain Res. 501, 183–187 (1989).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  238. 238.

    Smith, Q. R. & Johanson, C. E. Active transport of chloride by lateral ventricle choroid plexus of the rat. Am. J. Physiol 249, F470–F477 (1985).

    CAS  PubMed  PubMed Central  Google Scholar 

  239. 239.

    McCarthy, K. D. & Reed, D. J. The effect of acetazolamide and furosemide on cerebrospinal fluid production and choroid plexus carbonic anhydrase activity. J. Pharmacol. Exp. Ther. 189, 194–201 (1974).

    CAS  PubMed  PubMed Central  Google Scholar 

  240. 240.

    Melby, J. M., Miner, L. C. & Reed, D. J. Effect of acetazolamide and furosemide on the production and composition of cerebrospinal fluid from the cat choroid plexus. Can. J. Physiol. Pharmacol. 60, 405–409 (1982).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  241. 241.

    Vogh, B. P. & Langham, M. R. Jr. The effect of furosemide and bumetanide on cerebrospinal fluid formation. Brain Res. 221, 171–183 (1981).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  242. 242.

    Murphy, V. A. & Johanson, C. E. Acidosis, acetazolamide, and amiloride: effects on 22Na transfer across the blood-brain and blood-CSF barriers. J. Neurochem. 52, 1058–1063 (1989).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  243. 243.

    Macri, F. J., Politoff, A., Rubin, R., Dixon, R. & Rall, D. Preferential vasoconstrictor properties of acetazolamide on the arteries of the choroid plexus. Int. J. Neuropharmacol. 5, 109–115 (1966).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  244. 244.

    Swenson, E. R. New insights into carbonic anhydrase inhibition, vasodilation, and treatment of hypertensive-related diseases. Curr. Hypertens. Rep. 16, 467 (2014).

    PubMed  Article  CAS  PubMed Central  Google Scholar 

  245. 245.

    Francois, C. & Deprez, C. Ion transport and oxidative metabolism. I. The inhibition of mitochondrial oxidative metabolism by the unsubstituted aromatic sulfonamides (carbonic anhydrase inhibitors). Arch. Int. Physiol. Biochim. 79, 993–1007 (1971).

    CAS  PubMed  PubMed Central  Google Scholar 

  246. 246.

    Smith, Q. R. & Johanson, C. E. Chloride efflux from isolated choroid plexus. Brain Res. 562, 306–310 (1991).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  247. 247.

    Osswald, H. & Hawlina, A. Effects of acetazolamide and changes of acid-base balance on the content of cyclic nucleotides in the rat kidney. Pharmacology 19, 44–50 (1979).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  248. 248.

    Jacobs, S. et al. Mice with targeted Slc4a10 gene disruption have small brain ventricles and show reduced neuronal excitability. Proc. Natl Acad. Sci. USA 105, 311–316 (2008).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  249. 249.

    Kao, L. et al. Severe neurologic impairment in mice with targeted disruption of the electrogenic sodium bicarbonate cotransporter NBCe2 (Slc4a5 gene). J. Biol. Chem. 286, 32563–32574 (2011).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  250. 250.

    Damkier, H. H. & Praetorius, J. Genetic ablation of Slc4a10 alters the expression pattern of transporters involved in solute movement in the mouse choroid plexus. Am. J. Physiol. Cell Physiol. 302, C1452–C1459 (2012).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  251. 251.

    Bairamian, D., Johanson, C. E., Parmelee, J. T. & Epstein, M. H. Potassium cotransport with sodium and chloride in the choroid plexus. J. Neurochem. 56, 1623–1629 (1991).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  252. 252.

    Keep, R. F., Xiang, J. & Betz, A. L. Potassium cotransport at the rat choroid plexus. Am. J. Physiol. 267, C1616–C1622 (1994). This study demonstrated the outward transport direction of NKCC1 in the choroid plexus.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  253. 253.

    Kanaka, C. et al. The differential expression patterns of messenger RNAs encoding K-Cl cotransporters (KCC1,2) and Na-K-2Cl cotransporter (NKCC1) in the rat nervous system. Neuroscience 104, 933–946 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  254. 254.

    Karadsheh, M. F., Byun, N., Mount, D. B. & Delpire, E. Localization of the KCC4 potassium-chloride cotransporter in the nervous system. Neuroscience 123, 381–391 (2004).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  255. 255.

    Pearson, M. M., Lu, J., Mount, D. B. & Delpire, E. Localization of the K+-Cl cotransporter, KCC3, in the central and peripheral nervous systems: expression in the choroid plexus, large neurons and white matter tracts. Neuroscience 103, 481–491 (2001).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  256. 256.

    Ishikawa, A. et al. Altered electrolyte handling of the choroid plexus in rats with glycerol-induced acute renal failure. Biopharm. Drug Dispos. 31, 455–463 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  257. 257.

    Miller, T. B., Wilkinson, H. A., Rosenfeld, S. A. & Furuta, T. Intracranial hypertension and cerebrospinal fluid production in dogs: effects of furosemide. Exp. Neurol. 94, 66–80 (1986).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  258. 258.

    Vogh, B. P. & Doyle, A. S. The effect of carbonic anhydrase inhibitors and other drugs on sodium entry to cerebrospinal fluid. J. Pharmacol. Exp. Ther. 217, 51–56 (1981).

    CAS  PubMed  PubMed Central  Google Scholar 

  259. 259.

    Johnson, D. C., Singer, S., Hoop, B. & Kazemi, H. Chloride flux from blood to CSF: inhibition by furosemide and bumetanide. J. Appl. Physiol. 63, 1591–1600 (1987).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  260. 260.

    Alvarez-Leefmans, F. J. CrossTalk proposal: apical NKCC1 of choroid plexus epithelial cells works in the net inward flux mode under basal conditions, maintaining intracellular Cl and cell volume. J. Physiol. 598, 4733–4736 (2020).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  261. 261.

    Alvarez-Leefmans, F. J. Rebuttal from Francisco J. Alvarez-Leefmans. J. Physiol. 598, 4741–4742 (2020).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  262. 262.

    Gregoriades, J. M. C., Madaris, A., Alvarez, F. J. & Alvarez-Leefmans, F. J. Genetic and pharmacological inactivation of apical Na+-K+-2Cl cotransporter 1 in choroid plexus epithelial cells reveals the physiological function of the cotransporter. Am. J. Physiol. Cell Physiol. 316, C525–C544 (2019).

    PubMed  Article  PubMed Central  Google Scholar 

  263. 263.

    MacAulay, N. & Rose, C. R. CrossTalk opposing view: NKCC1 in the luminal membrane of choroid plexus is outwardly directed under basal conditions and contributes directly to cerebrospinal fluid secretion. J. Physiol. 598, 4737–4739 (2020).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  264. 264.

    MacAulay, N. & Rose, C. R. Rebuttal from Nanna MacAulay and Christine R. Rose. J. Physiol. 598, 4743 (2020).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  265. 265.

    Milhorat, T. H., Hammock, M. K., Fenstermacher, J. D. & Levin, V. A. Cerebrospinal fluid production by the choroid plexus and brain. Science 173, 330–332 (1971).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  266. 266.

    Mokgokong, R., Wang, S., Taylor, C. J., Barrand, M. A. & Hladky, S. B. Ion transporters in brain endothelial cells that contribute to formation of brain interstitial fluid. Pflug. Arch. 466, 887–901 (2014).

    CAS  Article  Google Scholar 

  267. 267.

    Oreskovic, D. & Klarica, M. The formation of cerebrospinal fluid: nearly a hundred years of interpretations and misinterpretations. Brain Res. Rev. 64, 241–262 (2010).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  268. 268.

    Butt, A. M., Jones, H. C. & Abbott, N. J. Electrical resistance across the blood-brain barrier in anaesthetized rats: a developmental study. J. Physiol. 429, 47–62 (1990).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  269. 269.

    Crone, C. & Olesen, S. P. Electrical resistance of brain microvascular endothelium. Brain Res. 241, 49–55 (1982).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  270. 270.

    Betz, A. L. & Goldstein, G. W. Specialized properties and solute transport in brain capillaries. Annu. Rev. Physiol. 48, 241–250 (1986).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  271. 271.

    Smith, Q. R. & Rapoport, S. I. Carrier-mediated transport of chloride across the blood-brain barrier. J. Neurochem. 42, 754–763 (1984).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  272. 272.

    Zador, Z., Stiver, S., Wang, V. & Manley, G. T. In: Aquaporins. Handbook of Experimental Pharmacology. 190 (ed Beitz, E.) 159-170 (Springer, (2009).

  273. 273.

    O’Donnell, M. E., Tran, L., Lam, T. I., Liu, X. B. & Anderson, S. E. Bumetanide inhibition of the blood-brain barrier Na-K-Cl cotransporter reduces edema formation in the rat middle cerebral artery occlusion model of stroke. J. Cereb. Blood Flow Metab. 24, 1046–1056 (2004).

    PubMed  Article  PubMed Central  Google Scholar 

  274. 274.

    Sun, D., Lytle, C. & O’Donnell, M. E. Astroglial cell-induced expression of Na-K-Cl cotransporter in brain microvascular endothelial cells. Am. J. Physiol. 269, C1506–C1512 (1995).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  275. 275.

    Shawahna, R. et al. Transcriptomic and quantitative proteomic analysis of transporters and drug metabolizing enzymes in freshly isolated human brain microvessels. Mol. Pharm. 8, 1332–1341 (2011).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  276. 276.

    Lane, J. R., Wigham, C. G. & Hodson, S. A. Determination of Na+/Cl-, Na+/HCO3- and Na+/K+/2Cl- co-transporter activity in corneal endothelial cell plasma membrane vesicles. Biochim. Biophys. Acta 1328, 237–242 (1997).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  277. 277.

    Oernbo, E. K. et al. Cerebral influx of Na+ and Cl- as the osmotherapy-mediated rebound response in rats. Fluids Barriers CNS 15, 27 (2018).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  278. 278.

    Simpson, I. A., Carruthers, A. & Vannucci, S. J. Supply and demand in cerebral energy metabolism: the role of nutrient transporters. J. Cereb. Blood Flow Metab. 27, 1766–1791 (2007).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  279. 279.

    Helms, H. C. C., Nielsen, C. U., Waagepetersen, H. S. & Brodin, B. Glutamate transporters in the blood-brain barrier. Adv. Neurobiol. 16, 297–314 (2017).

    PubMed  Article  PubMed Central  Google Scholar 

  280. 280.

    Smith, Q. R., Momma, S., Aoyagi, M. & Rapoport, S. I. Kinetics of neutral amino acid transport across the blood-brain barrier. J. Neurochem. 49, 1651–1658 (1987).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  281. 281.

    Smith, Q. R. Transport of glutamate and other amino acids at the blood-brain barrier. J. Nutr. 130, 1016S–1022S (2000).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  282. 282.

    Ohtsuki, S. New aspects of the blood-brain barrier transporters; its physiological roles in the central nervous system. Biol. Pharm. Bull. 27, 1489–1496 (2004).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  283. 283.

    Cornford, E. M. & Hyman, S. Localization of brain endothelial luminal and abluminal transporters with immunogold electron microscopy. NeuroRx. 2, 27–43 (2005).

    PubMed  PubMed Central  Article  Google Scholar 

  284. 284.

    Zeuthen, T., Zeuthen, E. & MacAulay, N. Water transport by GLUT2 expressed in Xenopus laevis oocytes. J. Physiol. 579, 345–361 (2007).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  285. 285.

    Betz, A. L., Firth, J. A. & Goldstein, G. W. Polarity of the blood-brain barrier: distribution of enzymes between the luminal and antiluminal membranes of brain capillary endothelial cells. Brain Res. 192, 17–28 (1980).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  286. 286.

    Lykke, K. et al. Evaluating the involvement of cerebral microvascular endothelial Na+/K+-ATPase and Na+-K+-2Cl- co-transporter in electrolyte fluxes in an in vitro blood-brain barrier model of dehydration. J. Cereb. Blood Flow Metab. 39, 497–512 (2019).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  287. 287.

    Vorbrodt, A. W. & Trowbridge, R. S. Ultracytochemical characteristics of cultured goat brain microvascular endothelial cells [corrected]. J. Histochem. Cytochem. 39, 1555–1563 (1991).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  288. 288.

    Goldstein, G. W. Relation of potassium transport to oxidative metabolism in isolated brain capillaries. J. Physiol. 286, 185–195 (1979).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  289. 289.

    Lin, J. D. Potassium transport in isolated cerebral microvessels from the rat. Jpn. J. Physiol. 35, 817–830 (1985).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  290. 290.

    Katzman, R. Maintenance of a constant brain extracellular potassium. Fed. Proc. 35, 1244–1247 (1976).

    CAS  PubMed  PubMed Central  Google Scholar 

  291. 291.

    Al Feteisi, H. et al. Identification and quantification of blood-brain barrier transporters in isolated rat brain microvessels. J. Neurochem. 146, 670–685 (2018).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  292. 292.

    Kubo, Y., Ohtsuki, S., Uchida, Y. & Terasaki, T. Quantitative determination of luminal and abluminal membrane distributions of transporters in porcine brain capillaries by plasma membrane fractionation and quantitative targeted proteomics. J. Pharm. Sci. 104, 3060–3068 (2015).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  293. 293.

    Cserr, H. F., DePasquale, M. & Patlak, C. S. Regulation of brain water and electrolytes during acute hyperosmolality in rats. Am. J. Physiol. 253, F522–F529 (1987). This study demonstrated the volume-regulatory ability of the brain barriers.

    CAS  PubMed  PubMed Central  Google Scholar 

  294. 294.

    Wald, A., Hochwald, G. M. & Malhan, C. The relationship between sodium influx and volume flow into the cerebral ventricles of cats. J. Neurochem. 25, 151–154 (1975).

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  295. 295.

    Stoica, A. et al. The α2β2 isoform combination dominates the astrocytic Na+/K+-ATPase activity and is rendered nonfunctional by the α2.G301R familial hemiplegic migraine type 2-associated mutation. Glia 65, 1777–1793 (2017).

    PubMed  Article  PubMed Central  Google Scholar 

  296. 296.

    Heo, J., Meng, F. & Hua, S. Z. Contribution of aquaporins to cellular water transport observed by a microfluidic cell volume sensor. Anal. Chem. 80, 6974–6980 (2008).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

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Acknowledgements

I would like to thank all the many great researchers, especially my mentor T. Zeuthen, with whom I have had the pleasure to discuss these topics with at length for the past few decades. I have learned so much from many of you! In addition, I would like to express my gratitude to my research team, past and present, for joining me on our quest to reach an understanding on how water crosses cell membranes in the brain. The work included in this Review was generously funded by the Lundbeck Foundation, the Independent Research Fund Denmark, the Novo Nordic Foundation, Thorberg’s Foundation, the Carlsberg Foundation, Friis’ Foundation, Danielsen’s Foundation, and the Hartmann Foundation.

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Nature Reviews Neuroscience thanks J. Badaut, R. Enger, who co-reviewed with L. Bordoni, and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Glossary

Dendritic beading

The bead-shaped swelling of dendrites during spreading depolarization.

Blood–brain barrier

(BBB). The tight junction-coupled endothelial cell layer that separates the circulating blood from the brain tissue.

Blood–CSF barrier

(BCSFB). The epithelial cell layer that separates the circulating blood from the cerebrospinal fluid (CSF)-filled ventricles.

Osmotic water permeability

The ease with which water crosses a cell membrane with a given transmembrane osmotic challenge.

Passive water transport

Water transport following the osmotic gradient.

Active water transport

Water transport taking place independently of — or even against — a transmembrane osmotic gradient.

Choroid plexus

The epithelial structures placed in the brain ventricles that secrete the majority of the CSF.

Activity-evoked extracellular space shrinkage

The cellular (glial) swelling taking place during neuronal activity, monitored as the size of the extracellular space.

Cotransport of water

The ability of cotransporters to translocate a fixed amount of water molecules in the direction of their transported solutes.

Elevated intracranial pressure

With brain fluid accumulation in pathology, the intracranial pressure increases due to the confinements of the brain within the skull; this condition can be life threatening.

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MacAulay, N. Molecular mechanisms of brain water transport. Nat Rev Neurosci (2021). https://doi.org/10.1038/s41583-021-00454-8

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