Figure 6.

Mutation of an S6 residue to enlarge the cavity relieved slowing of charge return and increased the rate of ionic deactivation kinetics. (A) Representative gating currents recorded from Kv1.2-I402C in the same conditions as Kv1.2 WT (Fig. 1 A) with NMG⁺_i. (B) Q_on-V and Q_off-V relationships with values for the Q_on-V of V_0.5 = −24.4 ± 2.3 mV, z = 2.9 ± 0.8 (n = 7) and for the Q_off-V of V_0.5 = −25.6 ± 2.3 mV, z = 1.7 ± 0.1 (n = 6). (C) Representative ionic currents recorded from Kv1.2-l402C. The G-V relationship for Kv1.2-I402C was plotted with the WT (gray dashes) for comparison. Kv1.2-I402C, V_0.5 = −1.1 ± 2.2 mV, z = 2.4 ± 0.1 (n = 5); P > 0.05 compared with WT. (D) To quantify the Ig_OFF rate, channels were depolarized to 0 mV for 50 ms to open channels, and the decay of Ig_OFF upon repolarization was fit with single exponential functions at potentials between −100 and −80 mV. Off rates (1/τ) were as follows: −80 mV, 1/τ = 369.8 ± 35.7 s⁻¹; −90 mV, 1/τ = 441 ± 25.7 s⁻¹; and at −100 mV, 1/τ = 511.2 ± 62.2 s⁻¹. The voltage dependence of the rate of charge was assessed by plotting the Ig_OFF rate against membrane voltage and fit with an exponential function of voltage (Eq. 1). (E) Representative normalized ionic tail currents recorded in 140 mM external K⁺ from Kv1.2 WT (black traces) and Kv1.2-I402C (gray traces) channels at −120 mV and −80 mV. Currents were recorded between −50 and −120 mV after a 50-ms pulse to 30 mV to open channels fully. The t_{0.5 decay} was plotted against the voltage to quantify the increased rate of Kv1.2-I402C deactivation kinetics. Error bars represent SEM.