Effect of TsVII on native Nav1.9 currents in rat DRG neurons. (A) Enhancement by 100 nM TsVII of TTX-r current evoked by steps to voltages between −55 and −35 mV. Control currents were recorded with a steady holding potential of either −80 mV (black traces) or −120 mV (blue traces), established for >5 min to remove inactivation from rNav1.9 channels. In both cases, the test pulse was preceded by a 400-ms step to −140 mV. 100 nM TsVII (green traces) was applied at the holding potential of −120 mV. (B) Peak conductance versus test voltage before and after 100 nM TsVII (different cell than A). Closed symbols, peak conductance calculated from peak current using a reversal potential of +50 mV; smooth curves, best fits to a Boltzmann function according to G = G_max/(1 + e^{−(V − V}_1/2^)/k), where G_max is the maximal conductance, V_1/2 is the half-activation voltage, and k is the slope factor. Control: G_max = 25 nS, V_1/2 = −34 mV, and k = 4.9 mV. 100 nM TsVII: G_max = 174 nS, V_1/2 = −54 mV, and k = 2.3 mV. (C) Voltage dependence of inactivation determined using a test pulse to −50 mV from a variety of holding potentials established for 2 s. Smooth curves are best fits to a Boltzmann function according to: I/I_max = (1 + e^{(V − V}_1/2^)/k)⁻¹, where I/I_max is the normalized peak conductance, V_1/2 is the midpoint of inactivation, and k is the slope factor. Control: V_1/2 = −45 mV and k = 6.2 mV. 100 nM TsVII: V_1/2 = −55 mV and k = 3.6 mV. All solutions contained 300 nM TTX to block TTX-s Nav channels.