Active H+ transport in the turtle urinary bladder. Coupling of transport to glucose oxidation.

Abstract

The turtle [Pseudemys scripta elegans] urinary bladder acidifies the contents of its lumen by activity transporting protons. H+ secretion by the isolated bladder was measured simultaneously with the rate of 14CO2 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 .**GRAPHIC**. The changes in JH and .**GRAPHIC**. were linear functions of the pH difference across the membrane. Hence, JH and .**GRAPHIC**. were linearly related to each other. The slope, .**GRAPHIC**. 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 .**GRAPHIC**. 2 experiments were performed in each of 14 hemibladders. In one, JH and .**GRAPHIC**. were altered by changing the luminal pH. In the other, they were altered by changing the ambient pCO2 while the luminal pH was kept constant. The average slope, .**GRAPHIC**. in the presence of pH gradients was 14.45 eq .cntdot. mol-1. In the absence of gradients in the same hemibladders it was 14.72, .DELTA. = 0.27 .+-. 1.46. H+ transport is organized so 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.