I136V mutation alters voltage-dependent activation and steady-state fast inactivation of NaV1.7 channels. A, Representative family traces of Na+ currents from voltage-clamped HEK293 cells expressing either wild-type NaV1.7R (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 NaV1.7R (n = 40) and I136V mutant (n = 43) channels. C, Comparison of the voltage-dependent activation and steady-state fast inactivation of NaV1.7R 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 V1/2,fast but altered the slope factor. D, Activation kinetics, measured as time-to-peak, were similar between NaV1.7R and I136V mutant channels. E, Fast inactivation kinetics of NaV1.7R 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 NaV1.7R channels. The inactivation kinetics of I136V channels are slower than that of NaV1.7R 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 NaV1.7R).
Cheng et al. Molecular Pain 2008 4:1 doi:10.1186/1744-8069-4-1