Slowing in I_gOFF and I_deac kinetics of Kv1.2 with prolonged depolarization times. (A) Deactivating gating (I_gOFF) currents upon 200-ms (top traces) and 5-s (bottom traces) prepulse depolarization times at 20 mV. Like the experiments on Shaker, the pulse protocols were ran in random order to avoid nonspecific effects on channel kinetics. (bottom) A superposition of I_gOFF at −120 and −90 mV upon 200-ms (black) and 5-s (red) depolarizations, respectively. (B) Ionic current deactivation after 200 ms (top traces) and 1 s (bottom traces) at 20 mV. (bottom) A superposition of scaled ionic currents at −80 and −50 mV upon 200-ms (black) and 1-s (red) depolarizations. (C) I_gOFF kinetics as a function of depolarization duration at 20 mV. Values were obtained by weighting the time constants from a double exponential fit to I_gOFF decay at different voltages (n = 5). (D) Voltage dependence of BC gate closure (I_deac) as a function of depolarization duration at 20 mV. The weighted I_deac kinetics obtained from a double exponential fit ± SEM (n = 7) are plotted. (E, top) The weighted I_gOFF kinetics at −60 mV as a function of prepulse depolarization time. Like Shaker, there were two noticeable slowing processes in I_gOFF kinetics, a fast τ_f of 13.5 ± 1.8 ms and a slow τ_s component of 1,120 ± 210 ms (n = 5). (bottom) Plot of the development of the weighted I_deac kinetics as a function of prepulse depolarization time. Like I_gOFF, there appeared two clear slowing processes, and fitting the relation with a double exponential function yielded a τ_f of 16.5 ± 6.1 ms and a τ_s of 1,250 ± 160 ms (n = 7). Error bars represent SEM.