Transport of H+ against electrochemical gradients in turtle urinary bladder

Active H+ transport (JH) by the isolated turtle bladder was inhibited by either an applied chemical gradient (deltapH) or an electrical gradient (deltapsi). The relation of JH to either deltapH or deltapsi was linear, and the slopes and the force gradients required to bring JH to zero were similar with both methods. The transport system was analyzed in terms of an equivalent circuit model comprising a proton motive force (PMF), an active conductance (LH) in series with the pump, and a parallel or passive conductance which may be ignored in this preparation. Increasing ambient PCO2 markedly increased JH and the active conductance (as deltaJH/deltadeltapH) but had no effect on the apparent PMF (PMF'). Similarly, acetazolamide caused comparable decreases in JH and LH without change in PMF'. Inhibition of metabolism by deoxygenation, deoxy-D-glucose, or depletion of metabolic substrate caused large decreases in JH and LH with reduction in PMF' of less than 14%. Glucose addition increased JH and LH but caused a slight decrease in PMF'. Thus, the experimental maneuvers affected the transport rate primarily through changes in the active conductance. Since PMF' was little affected, the force of the pump must be determined by factors other than the metabolic driving reaction alone. Conductance factors relating to transport as well as to metabolism participate in controlling PMF.