Fig. 6. Acid-activated apical Na⁺/H⁺ exchange rates in differentiated C2PLKO.1 cells. In these experiments, the apical side of the cell monolayer was perfused with Na⁺-containing buffer A, while the basal side with Na⁺-free buffer C during the pH_i-recovery period. (A) pH_i curve of apical pH_i recovery in the absence of inhibitors, (B) in the presence of 60 μM HOE642, (C) in the presence of 1 μM tenapanor, (D) in the presence of 60 μM HOE642 and 1 μM tenapanor in the apical perfusate in C2PLKO.1 cells. (E) comparisons of acid-activated apical Na⁺/H⁺ exchange rates without inhibitors, with 60 μM HOE642, 1 μM tenapanor, and 60 μM HOE642 plus 1 μM tenapanor. The total apical Na⁺/H⁺ exchange rate of C2PLKO.1 cells was 0.046 ± 0.003 (△pH/min). 60 μM HOE642 reduced acid-activated apical Na⁺/H⁺ exchange rates to 0.022 ±0.002 (△pH/min), 1 μM tenapanor to 0.032 ± 0.003 (△pH/min), and 60 μM HOE642 plus 1 μM tenapanor to 0.008 ± 0.001 (△pH/min). (F) Comparisons of initial pH_i at the beginning of acid-induced pH_i recovery among different groups. (n=5, mean ± SEM, one-way ANOVA with Tukey's multiple comparison tests, **p< 0.01, ***p<0.0001).