Fig. 3.

Alkaline pH shifts the voltage dependence of Na_VBP activation and state-steady inactivation of I_NavBP to more hyperpolarized potentials. (A) I_NavBP steady-state inactivation currents (pH 7.4). After a 4-s prepulse, the currents inactivated to a steady-state level and were reactivated by a second 4-s depolarizing pulse (–10 mV). V_HP = –100 mV. The intersweep interval was 20 s. (B) I_NavBP deactivation tail currents. After prepulses of varying depolarization (from –90 to + 20 mV, increments = +10 mV), tail currents were measured upon return to the holding potential (V_HP, –100 mV). The intersweep interval was 20 s. (C) Normalized activation curve and steady-state inactivation curve at pH 7.4 (black) and pH 9.0 (red). At pH 7.4 (V_HP =–100 mV), the half activation (V_1/2) is –35 ± 0.3mV (n = 16, ± SEM) with a slope factor (κ) of 7.8 ± 0.3 mV per e-fold change in current. At pH 9.0 (V_HP =–140 mV), activation V_1/2 is –64 ± 0.7 mV (n = 21), and κ is 5.8 ± 0.6 mV/e-fold. The 50% steady-state inactivation is –57 ± 0.3 mV (n = 14) and –86 ± 0.9 mV (n = 30) at pH 7.4 and 9.0, respectively. κ is 6.7 ± 0.3 and 7.7 ± 0.7 mV/e-fold for pH 7.4 and 9.0, respectively.