Schwartz T L, Kado R T
Prog Clin Biol Res. 1977;15:291-316.
A potassium-selective, chemically excitable channel, whose characteristics cannot be accurately described by "constant field" theory, is studied using a new approach based on diffusion theory but having no need for the classical assumptions of constant field, homogeneous membrane, and equal phase-boundary potentials at both interfaces. Permeability is defined, free of these constraints, and the Goldman coefficient is demonstrated to be a special case useful only when the constraints apply. Permeability can be evaluated directly from chord conductance, and it is found not to be a parameter in this channel, but rather a function of both the voltage and the concentration of the permeant ion. However, it becomes concentration-independent when the membrane voltage is equal to the sum of the phase-boundary potentials. That sum can therefore be determined from these data, and it is -65 mV in this channel. The permeability at that potential is a channel parameter, and equal to 8.77 (10)-6 cm/sec for this channel. A constant field is shown not to exist in this channel, and the Goldman coefficient not to be a parameter but a function of potential and concentration. Although errors introduced into this coefficient by nonconstant field and unequal surface potentials partially cancel each other, the coefficient is nevertheless not a correct measure of permeability.
研究了一种钾选择性、化学可兴奋通道，其特性无法用“恒定场”理论准确描述。采用一种基于扩散理论的新方法对其进行研究，该方法无需恒定场、均匀膜以及两个界面处相等相界电位的经典假设。在没有这些限制的情况下定义了渗透率，并证明戈德曼系数只是在这些限制条件适用时才有用的一种特殊情况。渗透率可直接从弦电导评估得出，发现它不是该通道的一个参数，而是电压和渗透离子浓度两者的函数。然而，当膜电压等于相界电位之和时，它就与浓度无关。因此，可根据这些数据确定该和，在这个通道中为 -65 mV。在该电位下的渗透率是一个通道参数，对于这个通道等于 8.77×10⁻⁶ cm/秒。结果表明这个通道中不存在恒定场，戈德曼系数不是一个参数，而是电位和浓度的函数。尽管非恒定场和不相等表面电位给该系数引入的误差部分相互抵消，但该系数仍不是渗透率的正确度量。
