AJP - Renal Physiology, Vol 261, Issue 5 753-F759, Copyright © 1991 by American Physiological Society
Maximal proton secretory rate of rat distal tubules is higher during chronic metabolic alkalosis
D. E. Wesson and G. M. Dolson
Veterans Affairs Medical Center, Baylor College of Medicine, Houston, Texas 77030-4298.
In vivo microperfusion studies show augmented proton secretion in the
distal tubule of rats with chronic metabolic alkalosis. The present studies
used the same technique to determine whether this augmented proton
secretion is due predominantly to an increase in substrate affinity or
alternatively to a predominant increase in the maximal proton secretory
rate. Surface distal tubules of alkalotic and control rats were
microperfused in vivo with solutions containing increasing concentrations
of HCO3. Proton secretion was determined as the difference between measured
net HCO3 reabsorption and passive HCO3 transport calculated by use of the
permeability derived from perfusing with a HCO3-free solution. Proton
secretion was expressed as a function of the initial luminal HCO3
concentration and was assumed to follow saturable Michaelis-Menten
kinetics. Alkalotic animals had a significantly higher Km (33.9 vs. 21.6
mM, P less than 0.03) and Vmax (223.8 vs. 99.1 pmol.mm-1.min-1, P less than
0.001) compared with control. These data are consistent with the augmented
proton secretion in the distal tubule of alkalotic animals as predominantly
due to an increased maximal proton secretory rate rather than to increased
substrate affinity.
