Inhibition of CLC-5 currents by extracellular H⁺’s. (A) CLC-5 currents recorded from the same oocyte at various pH_ex. Scale bars represent 1 µA and 10 ms. (B) Current–voltage plots for the currents shown in A. Squares, pH 9; circles, pH 7.5; triangles, pH 6.0; diamonds, pH 4.5. Solid lines hold no theoretical meaning. (C) Bar representation of the currents recorded at various voltages and pHs: black bar, I(pH 8, +70 mV); white bar, I(pH 7, +90 mV); hatched gray bar, I(pH 6, +110 mV). (D) Plot of normalized currents at +60 (filled circles) and +110 (open circles) mV as a function of pH. Solid lines are fits to Eq. 3 as described in Results, with K = 8.1 × 10⁻⁷, I_max = 1.02 and I_min = 0.27 at +60 mV, and K = 2.4 × 10⁻⁶, I_max = 0.99 and I_min = 0.33 at +110 mV. (E) Plot of the mean values of the pK obtained as in D, versus voltage. Solid line is a fit to pK(V) = pK(0) + zFV/RT, where pK(V) is the pK at voltage V, pK(0) = 6.6 is the pK extrapolated at V = 0, z = 0.51 is the fraction of the membrane potential acting on the blocking ion, and F, R, and T have their usual meanings.