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Astrocytes contain a vesicular compartment that is competent for regulated exocytosis of glutamate

Nature Neuroscience volume 7, pages 613–620 (2004)Cite this article

Abstract

Astrocytes establish rapid cell-to-cell communication through the release of chemical transmitters. The underlying mechanisms and functional significance of this release are, however, not well understood. Here we identify an astrocytic vesicular compartment that is competent for glutamate exocytosis. Using postembedding immunogold labeling of the rat hippocampus, we show that vesicular glutamate transporters (VGLUT1/2) and the vesicular SNARE protein, cellubrevin, are both expressed in small vesicular organelles that resemble synaptic vesicles of glutamatergic terminals. Astrocytic vesicles, which are not as densely packed as their neuronal counterparts, can be observed in small groups at sites adjacent to neuronal structures bearing glutamate receptors. Fluorescently tagged VGLUT-containing vesicles were studied dynamically in living astrocytes by total internal reflection fluorescence (TIRF) microscopy. After activation of metabotropic glutamate receptors, astrocytic vesicles underwent rapid (milliseconds) Ca2+- and SNARE-dependent exocytic fusion that was accompanied by glutamate release. These data document the existence of a Ca2+-dependent quantal glutamate release activity in glia that was previously considered to be specific to synapses.

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Figure 1: VGLUT-positive small vesicular organelles in astrocytic processes that face neuronal structures in the hippocampus.
Figure 2: Colocalization of VGLUTs and cellubrevin in astrocytic vesicles: proximity to neuronal membranes carrying NMDA receptors.
Figure 3: Colocalization of VGLUTs and cellubrevin in small vesicles in the processes of cultured astrocytes.
Figure 4: Exocytic fusions of VGLUT-positive vesicles monitored in living astrocytes.
Figure 5: Properties of mGluR-evoked exocytosis of VGLUT+ vesicles.
Figure 6: Astrocyte vesicle fusions evoke glutamate-dependent [Ca2+]i elevations in INS-1 cells.

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Acknowledgements

We thank H. Stubbe, Y. Gomez, K. Hüttmann and Centre de Microscopie Electronique, University of Lausanne for experimental support; J.-Y. Chatton, T. Coppola, P. Jourdain, G. Knott, T. Lang and R. Stoop for scientific discussions; R. Jahn, J. Storm-Mathisen for insights at various stages of this work and P. Clarke, J. Meldolesi, R. Regazzi and J. Storm-Mathisen for comments on the manuscript. This work was supported by grants OFES 00.0553 and FNRS 3100A0-100850/1 to A.V. and by Deutsche Forschungsgemeinschaft (SFB-TR3) and Fonds der Chemischen Industrie to C.S. V.G. is a visiting fellow within the European Community grant QLG3-CT-2001–2004 and recipient of a fellowship from the Norwegian Research Council.

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Author notes

  1. Paola Bezzi and Vidar Gundersen: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Cell Biology and Morphology, University of Lausanne, Rue du Bugnon 9, Lausanne, 1005, Switzerland

    Paola Bezzi, Vidar Gundersen, José Luis Galbete, Ethel Pilati & Andrea Volterra

  2. Cellular Imaging Facility UNIL-CHUV-Technological Development Unit, Rue du Bugnon 9, Lausanne, 1005, Switzerland

    Paola Bezzi & Andrea Volterra

  3. Anomical Institute and Centre for Molecular Biology and Neuroscience, University of Oslo, POB 1105 Blindern, Oslo, 0317, Norway

    Vidar Gundersen

  4. Department of Experimental Neurobiology, Neurosurgery, University of Bonn, Sigmund-Freud-Str. 25, Bonn, D-53105, Germany

    Gerald Seifert & Christian Steinhäuser

  5. Department of Pharmacological Sciences and Center of Excellence on Neurodegenerative Diseases, University of Milan, Via Balzaretti 9, Milan, 20133, Italy

    Andrea Volterra

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Supplementary information

Supplementary Fig. 1

Cumulative number of AO flashes plotted against time during a 3 min application of LTx (12 nM; n = 20; Supplementary Fig. 1a) or IONO (10 μM; n = 38; Supplementary Fig. 1b). (JPG 27 kb)

Supplementary Table 1 (PDF 9 kb)

Supplementary Note (PDF 23 kb)

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Bezzi, P., Gundersen, V., Galbete, J. et al. Astrocytes contain a vesicular compartment that is competent for regulated exocytosis of glutamate. Nat Neurosci 7, 613–620 (2004). https://doi.org/10.1038/nn1246

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