Figure 5. Recovery of Na+ currents from inactivation.
A, the recovery of the Na+ current was investigated with two-pulse protocols choosing recovery potentials ranging from -107 to -47 mV. The membrane was depolarized (-17 mV) for 14 ms and no leak subtraction was applied. The membrane holding potential was adjusted to the recovery potential 20 s before starting the stimulation protocol. The current amplitude of the test pulse was investigated following different recovery times limited by a maximal time of 100 ms (Aa) or 10 s (Ab, a different cell). Data from Aa were fitted with a monoexponential function a[1 - exp(t/τ1)], yielding a time constant of 18.9 ms. Data from Ab were fitted with a double-exponential recovery curve a1[1 - exp(t/τ1)]+a2[1 - exp(t/τ2)], with time constants τ1 and τ2 of 12 and 60 ms, respectively, and a1 and a2 values of 670 and 1060 pA, respectively. Ba, the voltage dependence of the recovery time constant derived from experiments with recovery times of 1-100 ms (○), and the shorter recovery time constant obtained from experiments with recovery times of 10 ms to 10 s (•). Bb, the voltage dependence of the second, longer time constant derived from double-exponential fits as shown in Ab. The error bars in Ba and Bb represent the standard error of the mean. Numbers in parentheses are numbers of cells.