Variations in pHo shift the voltage dependence curve. Experiments were performed on inside-out patches symmetrically bathed in NMDG-Cl solution. Pipette solution contained 5 mM Ca2+, and the bath solution was calcium free and adjusted at pH 7.4. (A) Current recordings from two separate patches under external (pipette) pH, pHo, 6.6 (left traces) or 8.0 (right traces) and clamped at the Vm values given on the left side. The dashed lines indicate the closed channel current levels (C-). (B) Mean N′Po/Vm relationships at pHo 6.6 (▲), 7.4 (●), and 8.0 (■). For each pHo condition, N′Po data were normalized to the respective value at Vm 80 mV. Each point is the mean of 5 (pHo 6.6 and 8.0) or 6 (pHo 7.4) measurements, and SEM is shown as error bars when larger than symbols. Continuous lines are nonlinear least squares fits of respective mean data with the Boltzmann equation. (C) Mean V1/2 values from Table 1 plotted as a function of pHo, and SEM is shown as error bars. Data were fitted by a straight line with a slope of 26.6 ± 1.99 mV/pHo unit (R2 = 0.989).
