Figure 3.

Onset of low-voltage inactivation and calculation of transitory and steady-state equilibrium constants. (A) Relative current amplitudes (I_test/I_control) plotted against prepulse duration on a semi-log scale. Pooled data are shown for Kv4.2 wt ([wt], black), the S4S5 and S6 single mutants [309] (green) and [412] (blue), and the corresponding double mutant [309:412] (red). Continuous lines represent double-exponential fits (leveling off at ss), and dotted lines represent the corresponding fast components in isolation (illustrating the transitory noninactivating current fraction 1 − a₁). (B and C) Equilibrium constants K_trans (B) and K_steady (C) were calculated from the noninactivating current fractions 1 − a₁ and ss, respectively (see Materials and Methods) and plotted logarithmically. The gray lines represent the function f(x) = x/(1 − x). Note that the mutation-induced effects on K_trans and K_steady are not additive for the coupling pair G309/I412.