Slc26a3 current is retained by Slc26a3(E367A). Cl⁻, NO₃⁻, and SCN⁻ (A–C) current by Slc26a3 and mutants was measured by a step protocol between −100 and +60 mV at 10-mV intervals from a holding potential of 0 mV. To obtain the I-V curves, oocyte bath in ND96 was perfused with ND96, and I-Vs were collected every minute for 5–10 min. The medium was then changed to a NO₃⁻-based medium, and I-Vs were recorded for 5–10 min. The bath solution was returned to ND96 until recovery of the basal Cl⁻ current. Finally, the solution was changed to the SCN⁻-based solution, and I-Vs were collected for 5–10 min. The I-V curves shown were obtained 5 min after the solution changes. Simultaneous measurement of Cl⁻/NO₃⁻ exchange (D) and the associated change in membrane potential (E), and Cl⁻/SCN⁻ exchange (F) and the associated change in membrane potential (G) were measured with Slc26a3 (dark traces and columns) and Slc26a3(E367A) (gray traces and columns). As indicated, the oocytes were perfused with ND96 (Cl⁻-containing) and then with the NO₃⁻- or SCN⁻-based solutions. The mean ± SEM of the ion flux rates (H) and associated changes in membrane potential (I) are given for the indicated number of experiments.