Ion channels – Membrane Transport – Integrative Physiology
Kidney International (1998) 54, 152–159; doi:10.1046/j.1523-1755.1998.00980.x
Characteristics of urea transport of cells derived from rabbit thick ascending limb of Henle's loop
R Willi Grunewald, Claudius H Reisse and Gerhard A Müller
Abteilung Nephrologie und Rheumatologie, Universitätsklinik Göttingen, Göttingen, Germany
Correspondence: R. Willi Grunewald, M.D., Abteilung Nephrologie und Rheumatologie, Universitätsklinik Göttingen, Robert Koch Str. 40, 37075 Göttingen, Germany
Received 9 July 1997; Revised 11 February 1998; Accepted 12 February 1998.
Abstract
Characteristics of urea transport in cells derived from rabbit thick ascending limb of Henle's loop.
Background
The thick ascending limb of Henle's loop (TALH) is thought to be involved in the regulation of the renal urea gradient.
Methods
We have characterized the uptake of urea (oil density centrifugation and 2-compartment-culture) and volume regulation (impedance measurement) in highly differentiated cells derived from rabbit outer medulla.
Results
TALH cells exposed to 600 mOsm/liter (300 mM urea) shrunk to 72 
5% of the isoosmotic volume. Due to a regulatory volume increase (RVI), the cell volume was almost completely regained at 92 6% after five minutes. The uptake of 14C-urea in the presence of urea concentrations up to 600 mM did not show any saturation. In the presence of phloretin the urea uptake decreased to 69 14%. The transport was sodium and chloride independent. Changing the membrane potential caused an increase of regulatory volume increase and urea uptake. Hyperosmolarity induced by sucrose (300 mM) and NaCl (150 mM) caused a decrease of urea uptake to 70 14% and 53 11%, respectively. The permeability coefficient (P) in a two compartment culture was P = 1.7 
10-6 0.39 10-6 cm/second, suggesting a relatively low permeability.
Conclusion
Due to the low permeability, it seems impossible to achieve a physiologically significant participation of the TALH in the urea circulation within the nephron. However, the results of this study provides significant hints about the existence of a specific urea transport mechanism that enables the cell to adapt rapidly to different osmolarities.
Keywords:
renal urea gradient, isoosmotic volume, hyperosmolarity, permeability, interstitium, TALH
