AJP - Renal Physiology, Vol 263, Issue 3 353-F362, Copyright © 1992 by American Physiological Society
Cell volume regulation in rat thin ascending limb of Henle's loop
L. F. Onuchic, I. R. Arenstein and A. G. Lopes
Department of Physiology, Faculdade de Medicina, Universidade de Sao Paulo, Brazil.
Thin ascending limb cells of Henle's loop from Wistar rats were studied
with in vitro microperfusion and video-optical techniques to investigate
their ability in regulating cell volume during osmotic shock and to
identify mechanisms of ion transport involved in the process. These cells
showed a clear volume regulatory decrease (VRD) response in hyposmotic
medium, but no volume regulatory increase in hyperosmotic medium. The
presence of barium in the bath abolished VRD. Removal of K+ from bath and
perfusate also inhibited the VRD response. Reintroduction of K+ in
hyposmotic conditions reestablished cell volume regulation. Introduction of
anthracene-9-COOH to the basolateral medium blocked cell volume regulatory
response. Cl- removal from perfusate and bath solutions also inhibited VRD,
probably because of a significant intracellular Cl- depletion. Exposure of
cells to ethylene glycol-bis(beta-aminoethyl ether)-N,N,N'N'-tetraacetic
acid in perfusate and bath solutions reduced significantly Ca2+
concentration and impaired VRD. Reintroduction of Ca2+ in hyposmotic
conditions restored volume regulation. The presence of ouabain in
basolateral medium also inhibited VRD. These data suggest that the
following mechanisms in the basolateral membrane are involved in VRD
response: K+ and Cl- conductive pathways, which might be Ca2+ dependent for
activation, and an Na(+)-K(+)-adenosinetriphosphatase.
