Rate constants of channel opening and closure. (A and B) Correlations between estimated rate constants of opening (A) and closure (B) and shifts of the activation curves (ΔV = V_1/2,MUT − V_1/2,WT) for IIS6 mutations. (C) Maximal time constants experimentally measured (open circles) and calculated (filled circles; see bell-shaped curves in Figs. 3 and 8) versus corresponding shifts of the activation curves. Lines represent fits by monoexponential functions (A₀ + A₁ * exp(−ΔV/k)), with A₀ = 1.57 ± 1.10, A₁ = 1.09 ± 0.52, and k =12.2 ± 1.9 for experimental data, and A₀ = 1.53 ± 0.95, A₁ = 0.88 ± 0.49, and k = 12.7 ± 2.3 for calculated data. (D) Voltage dependence of x(V) and y(V) plotted in semilogarithmic scale. x(V) represents the voltage dependence of the forward rate and y(V) the backward movement of the voltage-sensing machinery (see Fig. 1). A steeper voltage dependence of y(V) is evident.