Fig. 3.

Slow gating charge kinetics. (A) Representative recordings of gating currents evoked by 200-mV pulses with different durations from 0.04 to 120 ms. Each family of I_g was recorded with different voltage pulse protocol at the same voltage. (B, D, F, H, and J) OFF charge as function of voltage pulse duration for (α)BK and (α/βx)BK (x =1–4) channels. The OFF charge (Q_OFF; filled circles, mean ± SEM) was integrated in a range of 1 ms, normalized to the Q_MAX for each patch, and plotted against the pulse duration (time; logarithmic scale) for different voltage steps (40, 80, 120, 160, and 200 mV). The Q_OFF vs. t relation was fitted with a two-component exponential function (solid line) with time constant an amplitude of the fast component constrained to the exponential fit of I_gON at these voltages. (C, E, G, I, and K) Parameters defining the fast and slow components as a function of voltage for (α)BK and (α/βx)BK (x = 1–4) channels. For comparison the time constants of the I_K activation (τ_Ik, filled colored circles) are also shown. Time constants of the fast components of I_g (τ_fast) are represented by the open circles and the time constants of the slow components (τ_slow) are represented by the filled circles; A_slow* is the fractional amplitude of the slow components (A_slow* = A_slow/(A_fast + A_slow), open triangles), and C and E–G include the fits over the linear range of the I_K activation time constant reported by Orio and Latorre (20); solid black lines.