Active h+ transport in the turtle urinary bladder: Coupling of transport to glucose oxidation

Abstract

The turtle urinary bladder acidifies the contents of its lumen by actively transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14C02 evolution from [14C]glucose. The application of an adverse pH gradient resulted in a decline in the rate of H+ secretion (JH) and in the rate of glucose oxidation (JCo2)- The changes in JH and JCO2 were linear functions of the pH difference across the membrane. Hence, JH and J$0l were linearly related to each other. The slope, d/H/d/co2 was found to be similar in half-bladders from the same animal but was seen to vary widely in a population of turtles. To investigate the effect of pH gradients on aJH/aJco2. two experiments were performed in each of 14 hemibladders. In one JH and Jco2 were altered by changing the luminal pH. In the other, they were altered by changing the ambient pC02 while the luminal pH was kept constant. The average slope, aJHaJco2, in the presence of pH gradients was 14.45 eq-mol-1. In the absence of gradients in the same hemibladders it was 14.72, A = 0.27 ± 1.46. The results show that H+ transport is organized in such a way that leaks to protons in parallel to the pump are negligible. Analysis of the transport system by use of the Essig-Caplan linear irreversible thermodynamic formalism shows that the system is tightly coupled. The degree of coupling, q, given by that analysis was measured and found to be at or very near the maximum theoretical value. © 1976, Rockefeller University Press., All rights reserved.