Schauf C L, Davis F A
Biophys J. 1975 Nov;15(11):1111-6. doi: 10.1016/S0006-3495(75)85887-5.
In Myxicola axons subjected to moderate depolarizations the sodium inactivation time constants obtained from the decay of sodium current during a maintained depolarizatin (TSh) are substantially smaller than inactivation time constants determined at the same potential from the effect of changes in the duration of conditioning prepulses (Tph). This report extends these observations to positive membrane potentials and demonstrates that for sufficiently large depolarizations TSh and Tph become comparable. The ratio of inactivation time constants, Tph/TSh, is unaffected by changes in [Ca++] provided total divalent cation concentration is maintained constant, while changes in total divalent ion concentrations produce simple voltage shifts comparable to those obtained from measurement of membrane sodium or potassium conductances. Sodium inactivation delay was quantitatively determined as a function of membrane potential, and found to be similarly unaffected by changes in [Ca++] at constant total divalent ion concentration. Inactivation delay is, however, directly proportional to the activation rate constant over a wide range of potentials.
在受到适度去极化的黏液虫轴突中，在持续去极化期间从钠电流衰减获得的钠失活时间常数（TSh），显著小于在相同电位下根据条件预脉冲持续时间变化的影响所确定的失活时间常数（Tph）。本报告将这些观察结果扩展到正膜电位，并证明对于足够大的去极化，TSh和Tph变得相当。失活时间常数的比值Tph/TSh不受[Ca++]变化的影响，前提是总二价阳离子浓度保持恒定，而总二价离子浓度的变化产生的简单电压偏移与从膜钠或钾电导测量中获得的电压偏移相当。钠失活延迟被定量确定为膜电位的函数，发现在总二价离子浓度恒定的情况下，同样不受[Ca++]变化的影响。然而，在很宽的电位范围内，失活延迟与激活速率常数成正比。
