Figure 6: Cl⁻/HCO₃⁻ exchange activity in HEK293 cells expressing inducible AE1 protein.

(a) Time-course of fluorescence and pHi changes was monitored in HEK293 cells expressing (AE1+) or not AE1 (AE1−), with endogenous (grey) or endogenous plus recombinant (black) stomatin. Cells loaded with the fluorescent pH-sensitive probe BCECF-AM were submitted to inwardly-directed 10 mEq HCO3⁻/CO₂ and outwardly-directed 67.5 mEq Cl⁻ gradients at 30 °C. Data from five to eight time-courses were averaged. Smooth lines are monoexponential fits to the data using the simplex procedure of the Biokine (Bio-Logic), providing alkalinization rate constants (k, s⁻¹). (b) Values are means of constant k obtained in five independent experiments ± SEM. p values were determined with an unpaired t test from means obtained with induced cells. AE1− and AE1+ are non-induced or induced cells for AE1 expression, respectively. Stom+ and stom++ correspond to cells expressing endogenous and endogenous plus recombinant stomatin, respectively.