AJP - Renal Physiology, Vol 251, Issue 4 683-F689, Copyright © 1986 by American Physiological Society
Citrate transport in rabbit nephron
T. S. Brennan, S. Klahr and L. L. Hamm
Citrate is an important renal metabolic substrate and urinary inhibitor of
calcium stone formation. Our purpose was to characterize citrate
reabsorption in the rabbit nephron using isolated perfused tubules. Citrate
reabsorption, measured by luminal disappearance of [14C]citrate, was found
only in the proximal tubule, not in the cortical thick ascending limb or
the cortical collecting tubule. In the proximal convoluted tubule, the
collected fluid was also analyzed by thin-layer chromatography and by
measurements of chemical citrate concentration using an ultramicroassay.
Luminal disappearance of [14C]citrate was determined to accurately
represent citrate reabsorption; no significant citrate secretion was found.
The absolute magnitude of citrate reabsorption was approximately 3.4 pmol X
mm-1 X min-1 using either 1 or 3 mM citrate in the perfusate. This rate of
citrate reabsorption in the rabbit proximal tubule could account for all of
renal citrate reabsorption but was severalfold lower than glucose
reabsorption, which was studied for comparative purposes. In contrast, the
magnitude of succinate transport (which probably occurs via the same
transport system as citrate) was comparable with that of citrate. Citrate
reabsorption was inhibited approximately 80% by 10(-5) M ouabain. This
characterization of citrate transport in the intact proximal tubule should
provide a useful model to study regulation of urinary citrate excretion.
