AJP - Renal Physiology, Vol 251, Issue 1 150-F155, Copyright © 1986 by American Physiological Society
Morphological changes with Na+-free fluid absorption in isolated perfused snake tubules
W. H. Dantzler, O. H. Brokl, R. B. Nagle, D. J. Welling and L. W. Welling
Snake (Thamnophis spp.) proximal renal tubules were perfused and bathed in
vitro either with medium containing sodium or with medium in which the
sodium was replaced with choline. Net fluid absorption was measured by
changes in volume marker concentration, and cell volumes and cell membrane
surface areas were measured by ultrastructural morphometric methods. Net
fluid absorption did not differ significantly in the presence or absence of
sodium. However, during the 20-25-min perfusion in the absence of sodium,
significant morphological changes took place. The volume of the cells,
doubled and the volume of the intercellular spaces nearly quintupled. The
areas of the lateral and apical cell membranes approximately doubled, but
their surface densities remained essentially constant. Therefore the larger
cells in the absence of sodium had proportionally enlarged surface areas,
so that the volume-to-surface area ratio remained constant. These
morphological changes occurred concomitantly with the maintenance of net
fluid absorption and might play a permissive role in such maintenance in
the absence of sodium.
