α-Scorpion toxins interact with the rNa_v1.2a VSD IV paddle motif. (A) Shown is the effect of 100 nM AaHI, AaHII, LqqV, and BomIV on rNa_v1.2a channel function. Representative sodium currents were elicited by a 50-ms depolarization to a suitable membrane voltage (−20 to −15 mV) before (black) and after toxin addition (green) from a holding voltage of −90 mV. Clearly, toxin application results in a large persistent current component at the end of the test pulse. Fitting the current decay with a single-exponential function before and after toxin application yields fast inactivation time constants (τ) of 3.2 ± 0.1 and 4.7 ± 0.1 (AaHI); 3.6 ± 0.2 and 4.9 ± 0.1 (AaHII); 2.5 ± 0.1 and 4.6 ± 0.1 (LqqV); and 2.9 ± 0.1 and 8.5 ± 0.1 (BomIV), with n = 3 for each value (mean ± SEM). (B) Shown is the effect of 1 µM AaHI, LqqV, and BomIV on WT rK_v2.1. For each toxin, K⁺ currents were elicited by a 300-ms depolarization to 0 mV from a holding voltage of −90 mV (tail voltage was −60 mV). Currents are shown before (black) and in the presence of toxin (green). (C) Effect of 100 nM AaHI, LqqV, and BomIV on the rNa_v1.2a/K_v2.1 VSD IV paddle chimera. For each toxin, K⁺ currents (top) were elicited by a 300-ms depolarization near the foot of the voltage–activation curve (bottom) from a holding voltage of −90 mV. Currents are shown before (black) and in the presence of toxin (green). Representative normalized tail current voltage–activation relationships are shown (bottom), where tail current amplitude (I/I_max) is plotted against test voltage (V) before (black) and in the presence of toxins (green). A Boltzmann fit of the obtained data (n = 3; mean ± SEM) reveals a depolarizing shift in midpoint (V_1/2) of ∼15 mV for AaHI, >50 mV for LqqV, and ∼26 mV for BomIV. Holding voltage was −90 mV, and the tail voltage was −60 mV.