ATP-dependent H+ transport by the turtle bladder: NBD-C1 preferentially inhibits the vanadate-insensitive component in isolated membranes

We investigated the inhibitory effects of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) on ATP-dependent H+ accumulation by membrane vesicles prepared from the turtle urinary bladder epithelium. NBD-Cl at 30 microM was found to completely inhibit the vanadate-insensitive component of H+ transport, with half-maximal inhibition occurring at 4.2 to 5.4 microM. In contrast, the vanadate-inhibitable component was unaffected by 30 microM NBD-Cl. At high concentrations (300 microM), both components were fully inhibited. The results confirm the presence of two distinct H+ transport processes in turtle bladder membranes and identify selective inhibitors, NBD-Cl and vanadate, for each process.