Campbell D T, Hahin R
J Gen Physiol. 1984 Nov;84(5):771-88. doi: 10.1085/jgp.84.5.771.
The effect of low pH on the kinetics of Na channel ionic and gating currents was studied in frog skeletal muscle fibers. Lowering external pH from 7.4 to 5.0 slows the time course of Na current consistent with about a +25-mV shift in the voltage dependence of activation and inactivation time constants. Similar shifts in voltage dependence adequately describe the effects of low pH on the tail current time constant (+23.3 mV) and the gating charge vs. voltage relationship (+22.1 mV). A significantly smaller shift of +13.3 mV described the effect of pH 5.0 solution on the voltage dependence of steady state inactivation. Changes in the time course of gating current at low pH were complex and could not be described as a shift in voltage dependence. tau g, the time constant that describes the time course of the major component of gating charge movement, was slowed in pH 5.0 solution by a factor of approximately 3.5 for potentials from -60 to +45 mV. We conclude that the effects of low pH on Na channel gating cannot be attributed simply to a change in surface potential. Therefore, although it may be appropriate to describe the effect of low pH on some Na channel kinetic properties as a "shift" in voltage dependence, it is not appropriate to interpret such shifts as a measure of changes in surface potential. The maximum gating charge elicited from a holding potential of -150 mV was little affected by low pH.(ABSTRACT TRUNCATED AT 250 WORDS)
在青蛙骨骼肌纤维中研究了低pH对钠通道离子电流和门控电流动力学的影响。将细胞外pH从7.4降至5.0会减慢钠电流的时间进程，这与激活和失活时间常数的电压依赖性大约有+25 mV的偏移一致。电压依赖性的类似偏移充分描述了低pH对尾电流时间常数（+23.3 mV）和门控电荷与电压关系（+22.1 mV）的影响。+13.3 mV的显著较小偏移描述了pH 5.0溶液对稳态失活电压依赖性的影响。低pH下门控电流时间进程的变化很复杂，不能描述为电压依赖性的偏移。tau g是描述门控电荷移动主要成分时间进程的时间常数，在pH 5.0溶液中，对于-60至+45 mV的电位，其减慢了约3.5倍。我们得出结论，低pH对钠通道门控的影响不能简单地归因于表面电位的变化。因此，尽管将低pH对某些钠通道动力学特性的影响描述为电压依赖性的“偏移”可能是合适的，但将这种偏移解释为表面电位变化的度量是不合适的。从-150 mV的保持电位引出的最大门控电荷受低pH的影响很小。（摘要截断于250字）
