Figure 5. Kinetics of I_NaR activation and decay in GCs.

A, average I_NaR tracings at six selected potentials. These tracings are taken from those shown in Fig. 4B (note that here only the tracing region corresponding to the repolarizing pulses is shown; the preceding part of the protocol has been omitted). The repolarization level is specified next to each tracing. Smooth lines are second- (tracings 1–4) or first- (tracings 5 and 6) order exponential fittings to the currents' time course. The time constant of the exponential component describing the current's decay (τ_dec) is also specified next to each tracing. B, plot of I_NaR activation time constant (τ_act) as a function of V_test. τ_act values were returned by the fittings illustrated in A, in those cases in which I_NaR development was separated and distinguishable from I_NaP tails. C, plot of I_NaR time-to-peak (ttp) as a function of V_test. ttp was calculated taking the repolarizing pulse's starting point as time zero. Open circles and crossed circles correspond to ttp values obtained from measurements made in the presence and in the absence, respectively, of a true I_NaR peak region. In the latter case, the ‘peak’ region to be considered was chosen as illustrated in Fig. 4C (lowermost tracing). D, plot of I_NaR decay time constant (τ_dec) as a function of V_test.