Fig. 2.

Inward gating-pore current (Igp) were generated by mutations of the charged residues in the individual DI–DIV voltage-sensors of Na_v 1.5. (A) Typical current traces before (left) and after (right) 1 μM TTX treatment were elicited by 100-ms hyperpolarizing steps to various potentials that ranged from –200 to +40 mV in a 10-mV increment. The cells were held at –100 mV. The dotted line represents the zero current level. Linear leak and capacitance currents were not subtracted. (B) Effects of TTX on the current-voltage (I–V) curves of inward Igp. The subtraction of linear leak currents has been performed in the absence (filled circles) or presence (open circles) of 1 μM TTX. Igp were normalized to the maximal control Igp. (C) Activation threshold of Igp through the four voltage-sensors measured in the presence of TTX. (D) Effects of Gly mutations of gating-charge residues in four S4 segments on steady-state inactivation. The voltage dependence of steady-state inactivation was estimated using a standard double-pulse protocol. Currents were plotted as a fraction of the maximal peak current. Data points were fitted with a standard Boltzmann equation. (E) Ratio of Igp to the total central-pore current (I_Na). I_Na was estimated by the equation: I_Na = I_–100/hinf_–100, in which I_–100 is the maximal central-pore current when cells were held at –100 mV, and hinf_–100 is the fraction of the total sodium channels available at –100 mV on the basis of steady-state inactivation curve as shown in (D). *P < 0.05; ^#P < 0.01.