Keynes R D, Greeff N G, Forster I C
Station Biologique de Roscoff, France.
Philos Trans R Soc Lond B Biol Sci. 1992 Sep 29;337(1282):471-84. doi: 10.1098/rstb.1992.0122.
Comparisons were made between families of ion currents recorded in voltage-clamped squid axons dialysed with 20 mM NaF and 330 mM CsF or TMAF, and bathed in a solution in which four fifths of the Na was replaced by Tris. The permeability coefficient PNa,fast for the fast-inactivating current in the initial open state was calculated as a function of test potential from the size of the initial peak of INa. The permeability coefficient PNa,non for the non-inactivating open state was calculated from the steady-state INa that persisted until the end of the test pulse. Dialysis with TMA had no direct effect on the QV curve for gating charge. The reversal potential for INa,non was always lower than that for INa,fast, the mean difference being about -9 mV when dialysing with Cs, but only about -1 mV with TMA. Except close to threshold, PNa,fast was roughly halved by dialysis with TMA as compared with Cs, but PNa,non was substantially increased. The time constant tau h inactivation of the sodium system was slightly increased during dialysis with TMA in place of Cs, and there were small shifts in the steady-state inactivation curve, but the rate of recovery from inactivation was not measurably altered. The flattening off of the tau h curve at increasingly positive test potentials corresponded to a steady reduction of the apparent inactivation charge until a value of about 0.2e was reached for pulses to 100 mV. The instantaneous I-V relationship in the steady state was also investigated. The results have a useful bearing on the effects of dialysis with TMA, on the differences between the initial and steady open states of the sodium channel, and on the relative voltage-dependences of the transitions in each direction between the resting and inactivated states.
对用20 mM NaF和330 mM CsF或TMAF透析，并浸浴在五分之四的Na被Tris取代的溶液中的电压钳制乌贼轴突中记录的离子电流家族进行了比较。根据INa初始峰值的大小，计算了初始开放状态下快速失活电流的渗透系数PNa,fast作为测试电位的函数。从持续到测试脉冲结束的稳态INa计算非失活开放状态的渗透系数PNa,non。用TMA透析对门控电荷的QV曲线没有直接影响。INa,non的反转电位总是低于INa,fast的反转电位，用Cs透析时平均差异约为-9 mV，但用TMA透析时仅约为-1 mV。除了接近阈值外，与Cs相比，用TMA透析时PNa,fast大致减半，但PNa,non显著增加。用TMA代替Cs透析时，钠系统的失活时间常数tau h略有增加，稳态失活曲线有小的偏移，但失活恢复率没有明显改变。在越来越正的测试电位下，tau h曲线的平缓对应于表观失活电荷的稳定减少，直到脉冲到100 mV时达到约0.2e的值。还研究了稳态下的瞬时I-V关系。这些结果对于用TMA透析的影响、钠通道初始和稳定开放状态之间的差异以及静息态和失活态之间每个方向转换的相对电压依赖性具有重要意义。
