AJP - Renal Physiology, Vol 248, Issue 5 720-F728, Copyright © 1985 by American Physiological Society
Ammonia transport by the turtle bladder: relationship to H+ secretion
J. A. Arruda and G. Dytko
The turtle bladder is apparently capable of transporting ammonia in the
form of NH3 as well as NH+4. In the present study we examined the
relationship of ammonia transport into the mucosal solution to H+ secretion
and to chemical reactions in the unstirred layers. The relationship between
ammonia transport and H+ secretion was examined before and after inhibition
of H+ secretion by acetazolamide, SITS, and the putative inhibitor of the
H+ pump dicyclohexylcarbodiimide. All these inhibitors caused a significant
decrease in H+ secretion and led to a parallel decrease in the rate of
ammonia transport with serosal pH at 6.4. Stimulation of H+ secretion by 1%
CO2 increased both H+ secretion and ammonia transport at serosal pH 6.4. At
serosal pH 6.4 the changes in H+ secretion were highly correlated with
changes in ammonia transport. Ammonia transport at serosal pH 6.4 was
electrogenic and inhibited by a low mucosal pH. In contrast, the diffusion
of NH3 down an imposed concentration gradient was not correlated with
changes in H+ secretion. Chemical reactions in the unstirred layers seem to
influence ammonia transport in that increasing serosal nonvolatile buffer
concentrations decreased the diffusion of NH3 down the concentration
gradient from the serosal into the mucosal solution, probably by decreasing
serosal NH3 concentration. Conversely, addition of uncouplers in the
mucosal solution in an attempt to decrease the H+ concentration in the
mucosal solution unstirred layer decreased the ammonia transport at serosal
pH 6.4.
