AJP - Renal Physiology, Vol 250, Issue 4 680-F689, Copyright © 1986 by American Physiological Society
Dependence of ion fluxes on fluid transport by rat proximal tubule
K. Bomsztyk and F. S. Wright
The effects of changes in transepithelial water flux (Jv) on sodium,
chloride, calcium, and potassium transport by the proximal convoluted
tubule were examined by applying a microperfusion technique to surface
segments in kidneys of anesthetized rats. Perfusion solutions were prepared
with ion concentrations similar to those in fluid normally present in the
later parts of the proximal tubule. Osmolality of the perfusate was
adjusted with mannitol. With no mannitol in the perfusates, net fluid
absorption was observed. Addition of increasing amounts of mannitol first
reduced Jv to zero and then reversed net fluid flux. At the maximal rates
of fluid absorption, net absorption of Na, Cl, Ca, and K was observed. When
Jv was reduced to zero, Na, Cl, and Ca absorption were reduced and K
entered the lumen. Na, Cl, and Ca secretion occurred in association with
the highest rates of net fluid secretion. The lumen-positive
transepithelial potential progressively increased as the net fluid flux was
reduced to zero and then reversed. The results demonstrate that changes in
net water flux can affect Na, Cl, Ca, and K transport by the proximal
convoluted tubule of the rat kidney. These changes in net ion fluxes are
not entirely accounted for by changes in bulk-phase transepithelial
electrochemical gradients.
