DIV voltage-sensor movement is rate limiting for development of fast inactivation. (A) Representative families of traces illustrating current responses to a 0-mV test pulse after development of inactivation during a variable duration conditioning pulse at −30 mV. See Results for a detailed description of the voltage-pulse protocol. (B) Summary of the time course of development of fast inactivation for conditioning voltages spanning −120 to 0 mV. (C and D) For each conditioning voltage, the time course of development of fast inactivation shown in B was fit to the bi-exponential rise ${A1(1−e−(t−t0)/τ1)+A2(1−e−(t−t0)/τ2)}H(t−t0),$ where t is the duration of the conditioning pulse, A_i and τ_i are the amplitudes and time constants of the rise (i = 1,2), H is the unit step function, and t₀ is the delay after onset of the conditioning pulse to initiation of development of fast inactivation. The voltage dependence of the delay and fast time constant for each construct is summarized in C and D, respectively (mean ± SEM).