Figure 6. Temperature and pH dependence of sodium channels.
Left Example INa traces conducted by (A) NsvBa, (B) NaChBac, (C) NavBp and (D) Nav1.1 channels, when the extracellular saline (pH = 7.4 or 9.4) was heated from 20 to 37°C. Channels were activated by a 0.5 Hz voltage ramp. Voltage ramps were applied for different durations to compensate for different channel kinetics of activation and inactivation: NsvBa and NaChBac (100 ms); NavBp (200 ms) and Nav1.1 (10 ms). Right, Arrhenius plots with resulting peak current (plus symbols) and V1/2 (open squares) are graphed as a function of temperature. The peak currents were fit to a linear equation and the resulting slope (Peak Q10) given for both external pH conditions (n = 4).
Figure 6—figure supplement 1. The effect of temperature and pH on NsvBa selectivity.
(A) Top, Representative NsvBa current traces recorded at 34⁰C under different extracellular cationic conditions with a pH = 9. Currents were activated by increasing potentials from −10 mV to 70 mV from a holding potential of −140 mV. Bottom, Corresponding current–voltage relationships measured under the conditions listed above (n = 4 or 5 for each condition, Error = ±SEM). Peak inward currents were normalized to the Na+ current measured either in 110 or 150 mM extracellular solution. Erev was calculated by fitting the current from 0 mV to 60 mV to a linear equation, and determining the potential at zero current. When corrected for liquid junction potential differences in the salines, Erev under these conditions were 40 mV for 150 mM Na+; 36 mV for 110 mM Na+; 41 mV for 110 mM Ca2+ and 43 mV for 150 mM KCl. (B) The calculated relative permeability for cations measured at 22⁰C and 34⁰C.