FIGURE 1.

(A) Ultraslow recovery from inactivation in the mutation K1237C. Original traces of inward currents in an oocyte expressing K1237C channels. From a holding potential of −120 mV, the channels were inactivated by a depolarizing step to −20 mV of 300 s duration. After returning to −120 mV, recovery from inactivation was monitored by repetitive 20-ms steps to −10 mV at 20-s intervals. Peak inward currents were slowly rising approaching a maximum after several minutes. (B) Normalized time course of recovery from I_US. Peak inward currents from nine experiments as shown in A were normalized to the maximum current level after full recovery and plotted as a function of time after the conditioning prepulse. The time course of recovery was fitted with a double exponential function (Eq. 5). (C) Time course of development of ultraslow inactivation. The time course of recovery from I_US after varying prepulse durations was evaluated as in B (n = 4–12). The amplitudes of ultraslow recovery (A₂), as determined from fitting Eq. 5 to each time course of recovery, is plotted as a function of the duration of the conditioning prepulse. Data points were fitted with a monoexponential function (Eq. 6).