Rangarajan S K, de Levie R
Biophys J. 1979 Feb;25(2 Pt 1):235-52. doi: 10.1016/s0006-3495(79)85288-1.
It is shown that the constant field approximation must be amended to make it apply to time-dependent signals. The necessary additional term corresponds to the ionic displacement current. In the absence of adsorption, this ionic displacement current is found to have a characteristic time of the order of a fraction of a microsecond. We confirm its mathematical form as given by Cole (1965). When the membrane-soluble ions are strongly adsorbed, an additional, purely exponential transient of much larger time constant is calculated, with a time dependence identical to that of the translocation of adsorbed ions. Our results support the pseudostationary approximation used by Andersen and Fuchs (1975) in the description of such exponential transients. Explicit expressions are given for the current after a voltage step as for the admittance, both in the absence and presence of adsorption, for a membrane with a rectangular potential energy profile.
结果表明，必须修正恒定场近似，使其适用于随时间变化的信号。所需的附加项对应于离子位移电流。在没有吸附的情况下，发现这种离子位移电流具有约几微秒分之一的特征时间。我们确认了其由科尔（1965年）给出的数学形式。当膜溶性离子被强烈吸附时，计算出一个具有大得多的时间常数的附加纯指数瞬态，其时间依赖性与吸附离子的转运相同。我们的结果支持了安德森和富克斯（1975年）在描述这种指数瞬态时使用的准静态近似。对于具有矩形势能分布的膜，给出了在电压阶跃后电流以及导纳的明确表达式，包括在没有吸附和存在吸附的情况下。
