Fig. 5.

A, recovery from use-dependent block is determined by depolarizing voltage steps of 20 ms delivered 30 s and 1, 5, 10, and 15 min after use-dependent block is elicited by a 60-s, 1-Hz train of depolarizations. The wild type (○), Q399C (■), and F1236C (▲) data are fit to a single exponential curve with time constants of 9.44, 4.55, and 1.41 min, respectively. The current amplitudes before the pulse train were used for normalization. B, fractional recovery of the current. For the wild-type and each of the mutants, the fractional current at 15 min of recovery minus the fraction of current remaining after a 1-Hz train of depolarizing voltage steps to elicit use-dependent block is plotted. L396C, T397C, M398C, Q399C, and F1236C exhibit significantly larger fractional recoveries at 15 min compared with the wild-type.