FIGURE 6.

β subunits shift activation and inactivation of Na_v1. 7 channels. A, the normalized conductance was determined from the peak Na⁺ currents and is plotted versus the test potential. Also plotted is the steady-state inactivation obtained using 500-ms prepulses to voltages between −130 and −5 mV. The smooth curves are fits of the activation and inactivation data to Boltzmann functions with the parameters listed in Table 1. Data are the means ± S.E. of 14 (Na_v1.7), 26 (β₁), 9 (β₂), 21 (β₃), and 8 (β₄) determinations. B, Na⁺ channels were inactivated by a brief depolarization (−30 mV/20 ms), and the recovery time course (0–1200 ms) was measured at −100 mV. The smooth curves are biexponential curve fits with the fast and slow time constants listed in Table 1. Data are the means ± S.E. of 15 (Na_v1.7), 22 (β₁), 10 (β₂), 17 (β₃), and 8 (β₄) determinations. C, window current probabilities predicted from the activation and steady-state inactivation of the Na_v1.7 channels expressed alone or with either the β₁ or β₃ subunits.