FIGURE 2.

Internal protons do not alter the uncoupling effect of external SCN⁻. A, representative recordings of time- and voltage-dependent internal alkalinization in a cell expressing ClC-5. Lines represent linear fits to the data. B, representative recordings of time-dependent ClC-5-mediated intracellular alkalinization at +120 mV at symmetric pH 7.4 (upper panel) and pH 6.3 (lower panel). C and D, rates of intracellular pH change in external Cl⁻ and SCN⁻ at symmetric pH 7.4 (C) and pH 6.3 (D) normalized to the value in Cl⁻ at +120 mV. Rates were determined using the slope of the linear fits to the data, as shown in A. Averaged proton flux densities at +120 mV and symmetric pH 7.4 were 9.8 × 10⁻³ ± 1.3 × 10⁻³ ΔpH s⁻¹ pF⁻¹ for external Cl⁻ (n = 17) and 10.2 × 10⁻³ ± 1.1 × 10⁻³ ΔpH s⁻¹ pF⁻¹ for SCN⁻ (n = 14). The corresponding averaged proton flux densities at symmetric pH 6.3 were 1.9 × 10⁻³ ± 0.5 × 10⁻³ ΔpH s⁻¹ pF⁻¹ for external Cl⁻ (n = 6) and 4.3 × 10⁻³ ± 1.0 × 10⁻³ ΔpH s⁻¹ pF⁻¹ for SCN⁻ (n = 6). E and F, relative transport coupling of WT ClC-5 in external Cl⁻ and SCN⁻. Currents were normalized to +120 mV in Cl⁻ and divided by the normalized proton fluxes at the same voltage at symmetric pH 7.4 (E; n = 6–17) and symmetric pH 6.3 (F; n = 4–5). Asterisks indicate significant differences: ***, p < 0.001; **, p < 0.01; *, p < 0.05 (paired t test for non-normalized cells measured in both extracellular solutions at the same voltage). n.d., not determined.