Fig. 2.

Na_VBP is a voltage-gated Na⁺ channel modulated by extracellular alkaline pH. (A) Representative traces (Upper) of I_NavBP activated by the voltage protocol shown. Holding potential (V_HP =–100 mV). The cell was bathed in 10 mM Ca²⁺ external solution (140 mM Na⁺ /10 mM Ca²⁺/5mMK⁺ pipette; 147 mM Cs⁺ /8mMNa⁺ ; see Materials and Methods). (B) Averaged peak current–voltage (I–V) relation of Na_VBP in standard bath solution at pH 7.4 (blue, n = 19, V_HP = –100 mV), and pH 9.0 (red, n = 11, V_HP =–130 mV), normalized by cell capacitance (pF). (C) Increasing pH_o reversibly potentiated I_NavBP generated by a ramp protocol (–140 mV to + 100 mV in 380 ms, V_HP =–140 mV). (D) pH_o-dependent changes on the normalized amplitude of the peak inward current (n = 9; ± SEM). The pH_o-dependent shifts of the peak voltage is plotted (Inset).