Figure 1.

I136V mutation alters voltage-dependent activation and steady-state fast inactivation of Na_V1.7 channels. A, Representative family traces of Na+ currents from voltage-clamped HEK293 cells expressing either wild-type Na_V1.7_R (top) or I136V mutant (bottom) channels. Cells were held at -100 mV, and Na⁺ currents were elicited by step depolarizations from -80 to +60 mV in 5 mV increment every 5 seconds. B, Normalized peak current-voltage relationship for Na_V1.7_R (n = 40) and I136V mutant (n = 43) channels. C, Comparison of the voltage-dependent activation and steady-state fast inactivation of Na_V1.7_R and I136V mutant channels. A hyperpolarizing shift (-5.7 mV) of activation was observed in I136V mutant channels. Steady-state fast inactivation was examined using a series of 500-ms prepulses from -140 mV to -10 mV followed by 40-ms test pulses at -10 mV. I136V mutation did not change the V_1/2,fast but altered the slope factor. D, Activation kinetics, measured as time-to-peak, were similar between Na_V1.7_R and I136V mutant channels. E, Fast inactivation kinetics of Na_V1.7_R and I136V mutant channels. Inactivation time constants were calculated by fitting the decay phases of currents shown in Figure 1A with single-exponential function. Gray circles represent I136V shifted 5.7 mV in a depolarizing direction to match the voltage-dependent activation of wild type Na_V1.7_R channels. The inactivation kinetics of I136V channels are slower than that of Na_V1.7_R channels. F, Expanded view of overlap of activation and inactivation Boltzmann fits (area as predicted window current) from C (shaded area for I136V mutation, and lined area for Na_V1.7_R).