E357 is crucial for all forms of Cl⁻-coupled exchange by Slc26a6. (A) Surface expression of Slc26a6 mutants expressed in HEK cells. The expression of the cytoplasmic GAPDH serves as loading and biotinylation controls. (B) Example traces of Cl⁻_i (green), pH_i (blue), and membrane potential (red) measured in oocytes expressing Slc26a6(E357A). (C) The summary of flux rates measured with Slc26a6, Slc26a6(E357D), Slc26a6(E357A), and Slc26a6(E357K). (D) Individual traces and (E) the summary of oxalate current as a result of oxalate⁼/Cl⁻_i exchange mediated by the indicated Slc26a6 mutants measured in the absence of Cl⁻_o and the presence of 5 mM bath oxalate⁼. (F) Individual traces and (G) the summary of Cl⁻_i/formate⁻ exchange by the indicated Slc26a6 mutants, measured as formate⁻-driven Cl⁻ efflux. Results in summaries are given as mean ± SEM of the number of experiments listed in the columns.