AJP - Renal Physiology, Vol 247, Issue 4 575-F581, Copyright © 1984 by American Physiological Society
Interactions between phosphate and oxidative metabolism in proximal renal tubules
P. C. Brazy, L. J. Mandel, S. R. Gullans and S. P. Soltoff
These studies examine the phosphate dependence of fluid absorption and
oxidative metabolism in proximal tubules from rabbit kidney. Removal of
inorganic phosphate from intraluminal fluid in isolated perfused tubules
reduced fluid absorption (Jv) from 1.0 nl X mm-1 X min-1 to zero and
removal of phosphate from the medium bathing tubules in suspension reduced
O2 consumption rates (coupled, uncoupled, ouabain sensitive, and ouabain
insensitive) and ATP contents by 30-40%. Inhibitions induced by removal of
phosphate could be altered by addition of selected organic substrates to
ambient fluids. Addition of succinate, citrate, or malate preserved
uncoupled respiration and partially preserved Jv (0.4-0.9 nl X mm-1 X
min-1), with succinate being most effective. Addition of short-chain fatty
acids (butyrate or valerate) to phosphate-free media had little or no
effect on Jv. n-Butylmalonate, an inhibitor of dicarboxylate anion
transport into mitochondria, reduced oxidative metabolism, ATP content, and
Jv when added to phosphate-containing media but had no further effect on
these tubular functions when added to phosphate-free media. Together these
results suggest that phosphate limitation reduces dicarboxylate anion
availability to mitochondria and that this inhibition may contribute to the
overall reduction in oxidative metabolism and Jv observed under these
conditions.
