AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 5 982-R988, Copyright © 1989 by American Physiological Society
Membrane dynamics in relation to fluid absorption in reptilian proximal renal tubules
W. H. Dantzler
Department of Physiology, College of Medicine, University of Arizona, Tucson 85724.
Net fluid absorption (Jv), cell volume, and cell membrane area have been
studied in isolated, perfused snake (Thamnophis spp.) proximal tubules.
With Na+ in both perfusate and bathing medium, Jv averages approximately
0.9 nl.min-1.mm-1. When choline replaces Na+ in perfusate, Jv nearly
ceases. When choline also replaces Na+ in bathing medium, so that both
solutions are identical, Jv returns to the control rate. The results are
the same when tetramethylammonium replaces Na+, when sucrose replaces Na+
and the equivalent amount of Cl-, and when methyl sulfate replaces Cl-
alone. However, when Li+ replaces Na+ in perfusate alone or in both
perfusate and bathing medium, Jv is unchanged. Jv at control rates is
isosmotic and can be partially inhibited by cold and cyanide. When choline
replaces Na+ in perfusate and bathing medium, cell volume doubles, and
intercellular space volume nearly quintuples. The areas of the lateral and
apical cell membranes also approximately double, so that the surface
area-to-volume ratio remains constant. These morphological changes in the
absence of Na+ occur concomitantly with maintenance of Jv, suggesting that
they may play a permissive role in such maintenance.
