AJP - Renal Physiology, Vol 245, Issue 5 535-F544, Copyright © 1983 by American Physiological Society
Application of the disequilibrium pH method to investigate the mechanism of urinary acidification
T. D. DuBose Jr
DuBose, Thomas D., Jr. Application of the disequilibrium pH method to
investigate the mechanism of urinary acidification. Am. J. Physiol. 245
(Renal Fluid Electrolyte Physiol. 14): F535-F544, 1983.--The cellular
mechanism of renal bicarbonate reabsorption has been debated for four
decades. Recent technological advances have allowed distinction between
primary bicarbonate reabsorption and a proton secretory mechanism. The
disequilibrium pH method has been applied widely for this purpose and has
supported the latter hypothesis uniformly. The demonstration of elevated
values for PCO2 in tubular and vascular structures of the renal cortex has
not altered this view. Indeed, by employing a newly developed method for
measurement of equilibrium pH in vivo that permits contact with the
environment within the tubule lumen to continue, we demonstrated an acid
disequilibrium pH in the proximal tubule after carbonic anhydrase
inhibition equal to -0.68 pH units. A spontaneous disequilibrium pH was not
present in the distal tubule during control conditions or during metabolic
alkalosis but was demonstrated during combined respiratory
acidosis-metabolic alkalosis. This finding agrees qualitatively with
observed rates of bicarbonate reabsorption in the perfused distal tubule in
vivo. With use of similar techniques, an acid disequilibrium pH in
conjunction with elevated values for PCO2 was observed in the papillary
collecting duct. Thus, proton secretion appears to be the predominant
mechanism of bicarbonate reabsorption in superficial nephrons and explains,
as well, the means by which the urine-to-blood PCO2 gradient in alkaline
urine is established.
