Inhibition of HCO₃⁻ fluxes across the apical membrane of guinea pig pancreatic ducts by CFTR_inh-172. Membrane potential–evoked changes in pH_i in the presence or absence of 5 µM of luminal CFTR_inh-172 as indicated. Experimental conditions were similar to those in Fig. 1 D. (A) Reduced rate of increase in pH_i evoked by depolarization with 70 mM K⁺ when CFTR_inh-172 was added to the luminal perfusate. (B) Recovery of pH_i increase evoked by 70 mM K⁺ when CFTR_inh-172 was removed from the luminal perfusate. Representative of six experiments.