Figure 4.

Recovery from inactivation at −80 mV in the WT, p.I136V, p.I848T, and p.V1316A mutant channels at 15 °C and 25 °C. (A) The cell was held at −120 mV and pulsed twice to +20 mV (each for 10 ms) every 1.5 sec, with a gradually lengthened gap between the two pulses at −80 mV (the recovery voltage, V_r). The sweeps are arranged so that the currents in the second pulse are gradually shifted rightward as the gap was lengthened (by 0.1 ms between each sweep). (B) The fraction recovered is defined as the ratio between the peak current in the second pulse and that in the first pulse from the experiments in part A and is plotted against the duration of V_r to make the time course of recovery from inactivation. Note the evidently faster recovery in the WT than in the p.I136V, p.I848T, and p.V1316A mutant channels at 15 °C but not at 25 °C. Inset, first 60 ms data are redrawn with a smaller horizontal scales to demonstrate that the significantly faster recovery in the WT channel than in the mutant channels at 15 °C. (C) The time courses of recovery from inactivation in part B are fitted with a mono–exponential equation. Cumulative results of the time constants from the fits (each n = 4–5 for measurement) show that the recovery from inactivation at −80 mV is much faster at 25 °C than that at 15 °C in all channels, but is significant different between the WT and the mutant channels only at 15 °C but not at 25 °C (*p < 0.05).