Figure 1. Effect of N-terminal SNAP-25 domains on Kv2.1 channel gating.

(A) S180 and S197 accelerate the rate of current activation compared with control SNAP-25. Whole-cell normalized Kv2.1 current traces in HEK-293 cells in the absence and presence of GST (control), S180 or S197 (1 nM) are shown. Activation rates were measured from currents evoked by a 200 ms stepwise depolarization to +50 mV from a holding potential of −70 mV. Currents were fit with the monoexponential function I=A*exp^−t/τ, where A is the amplitude, t is time and τ is the time constant. Summarized activation time constants (activation τ) of Kv2.1 using control, S180, S197 and S206 are shown in panel (B). (C) S180 and S197 but not S206 slow Kv2.1 current inactivation. Inactivation rates were determined from current evoked by a 10 s stepwise depolarization to +50 mV from a holding potential of −70 mV, and fit with a monoexponential function. (D) The summarized inactivation time constants (inactivation τ). (E) The voltage dependence of channel activation. Tail currents were measured at −70 mV following the 200 ms stepwise depolarizations from −70 to +70 mV. Data were fit with the Boltzmann function I/I_max=1/{1+exp[(V−V_1/2)/k]}, where V_1/2 is the half-maximal inactivation potential and k is the slope factor. *, P<0.05.