pHi modulates the number of active channels. (A) Representative continuous current recording from an inside-out membrane patch at Vm 80 mV, symmetrically bathed in NMDG-Cl solution. Pipette solution contained 5 mM Ca2+ (pH 7.4), and pHi was varied as indicated. The inset contains two excerpts taken at the indicated locations (a and b) at the expanded time and amplitude scales (*). The dashed lines indicate the closed channel current levels (C-). (B) Time course of the change in channel activity upon switching pHi from 7.8 to 6.8 (arrow), at Vm 80 mV. The dashed line indicates the closed channel current level (C-). The fit of the trace under pHi 6.8 to a single exponential equation (continuous line) indicated an e-fold decrease in channel activity after 17.1s. (C) N′Po, number of active channels (N′) and Po as a function of pHi. Paired data were obtained as described in A and normalized to the respective value at pHi 7.8. N′ was determined by peak current measurements and validated by stationary noise analysis (see Materials and methods). Only recordings yielding ΔN′/N′ values within the 95% agreement interval were taken as valid. Data are given as means from four patches, and SEM is shown as error bars. N′Po, N′, and Po means significantly were affected by pHi (P < 0.001, P < 0.001, and P = 0.005, respectively; one-way ANOVA). **, P < 0.001; and *, P < 0.02 versus pHi 7.8 (Holm-Šidák multiple comparison procedure).
