Na⁺ dependence of the Cl⁻/HCO₃⁻ exchanger in SMG acinar cells from the Ae2^−/− mouse. (A) pH_i measurements performed on isolated acinar cells loaded with the pH indicator BCECF-AM. An intracellular alkalinization was observed in Ae2^−/− cells in response to a reduction in [Cl⁻]_o in the presence of external Na⁺ (black circles; n = 8; switching from solution A to B [Table 1]). In contrast, little, if any, alkalinization was observed in the absence of external Na⁺ in Ae2^−/− cells (green circles; n = 7; switching from solution C to D [Table 1]) or in Ae2^−/−-Ae4^−/− cells using a Na⁺-containing external solution (blue circles; n = 8; switching from solution A to B [Table 1]). Exchanger activity was calculated by linear regression analysis of the initial alkalinization response induced by a reduction in [Cl⁻]_i (discontinuous red lines). Results are presented as the mean ± SEM. (B) Summary of experiments as shown in A. Data are expressed as the mean ± SEM of at least five acinar cells per experiment from at least three cell preparations. For Ae2^−/− mice, the black bar is significantly greater, “a” compared with “b” (P < 0.05, one-way ANOVA followed by Bonferroni’s post hoc test).