Anion/proton transport stoichiometry of ClC-4 increases with reduced apparent anion binding affinity. (A) Representative current–voltage relationship from a cell perfused with extracellular solutions containing various SCN⁻ concentrations. Current–voltage relationships were obtained by applying 100-ms voltage ramps from −50 to +135 mV. (B) Dependence of the macroscopic current amplitude at +130 mV on the external anion concentration for various external anions (n = 4–7). Lines represent fits with Michaelis-Menten equation to obtain apparent saturation constants. (C) Relative anion/proton coupling as determined in Fig. 1 F plotted against the measured apparent Michaelis constant for various external anions.