Cl⁻ and Na⁺ dependence of HCO₃⁻ fluxes across the apical membrane of guinea pig pancreatic ducts. (A) Membrane potential–evoked changes in pH_i in the absence of Cl⁻. To deplete intracellular Cl⁻, the bath and lumen were perfused with the Cl⁻-free, HEPES-buffered solution in the presence of dbcAMP for 30 min before the measurements. Experimental conditions were similar to those in Fig. 1 D, but with Cl⁻ replaced by glucuronate in both the bath and luminal perfusates. Representative of four experiments. (B) Membrane potential–evoked changes in pH_i in the absence of luminal Na⁺. Experiments were similar to those shown in Fig. 1, but with Na⁺ replaced by NMDG in the luminal perfusate. Representative of four experiments.