Fig. 3

Electrophysiology of voltage-gated Na channel. Extracellular solution contained 114.8 mM Na. Pipette solution contained Cs. V _h = −100 mV. Averaged traces from 3 recordings. Leak currents in a–d were subtracted by use of the P/4 function supplied with pClamp. Error bars indicate SD. a Currents induced by varied voltage steps. Command voltages were increased in 10 mV steps from −150 to +90 mV. The duration of depolarization pulses was 20 ms (step bar). b I–V relationship for the voltage-gated Na current. Peak currents in a were plotted against membrane potentials. Reversal potential was 56.0 mV. c Activation curve. The activation curves of I _Na were well fitted by the Boltzmann function (see text). Half-activation voltage was −32.5 mV. d Inactivation curve. Relative conductances were obtained from the current generated when the −10 mV (100 ms) depolarization pulse was given just after a −150 to 50 mV (1 s) prepulse. The curve was fitted by the same equation as for c. Half-inactivation voltage was −61.9 mV. e Superimposition of current traces evoked by 100 times depolarization pulse. The depolarization pulse was −10 mV (V _h = −100 mV). Red line show the average of the currents that was obtained from 100 times recordings. f Variance–mean current plot. Data between 2.2 and 5.1 ms in e were plotted. Red trace is a fit by \( \sigma^{2} = iI - I^{2} /n \) (σ ²: variance, i: single-channel current, I: mean current, n: number of channels in a cell), with n = 2346, i = 0.22 pA. The data were R ² = 0.97 from the least-squares fitting and χ ² = 1.57 from the chi-squared test