Fig. 1.
ML277 activates the KCNQ1 channel. (A) Left, the KCNQ1 activation currents exhibit two phases: a fast phase approximates the intermediate-open (IO) state, and the slow phase approximates the activated-open (AO) state. The depolarization voltages were from −120 to +60 mV in 20 mV increments for 4 s and then stepped back to −40 mV to record the tail currents. Right, a five-state kinetic model recapitulates the unique gating process of the KCNQ1 channel (RC: resting closed, IC: intermediate closed, AC: activated closed). (B) Left, 1 µM ML277 activates the KCNQ1 currents. Current recorded before (black) and after (blue) adding ML277 were superimposed to show the ML277 effects. Right, ML277 enhances the VSD-PD coupling transition of the AO state. (C) Averaged current–voltage (I–V) relations of KCNQ1 channel before (black, n = 6) and after (blue, n = 6) adding ML277. (D) Normalized G–V relations of KCNQ1 channel before (black, n = 6) and after (blue, n = 6) adding ML277. Data points were fitted with a Boltzmann equation. (E) Left, activation and deactivation time constants (τ) of KCNQ1 currents before (black) and after (blue) adding ML277. The voltage was +60 mV for 4 s to activate KCNQ1 and then stepped to –120 mV for 2 s to deactivate KCNQ1. The activation time constants of the fast phase (τf) and slow phase (τs) were 25 and 563 ms for control, and 28 and 952 ms after adding ML277. The deactivation time constants (τd) were 103 ms for control and 207 ms after adding ML277. Right, averaged results of time constants (τf, τs, and τd) of KCNQ1 currents before (black) and after (blue) adding ML277 (n ≥ 8). n.s.: nonsignificant. The P values are 0.69 for τf, 0.00073 for τs, and 0.00011 for τd.