Schwartz T L, Kado R T
Biophys J. 1977 Jun;18(3):323-49. doi: 10.1016/S0006-3495(77)85617-8.
A potassium-selective, chemically excitable channel, whose characteristics cannot be accurately described by constant-field theory, is studied by a new approach based on diffusion theory but with 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 current-voltage data, 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 8.66 X 10(-6) cm/s 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.
研究了一种钾离子选择性、化学可激发通道，其特性无法用恒场理论准确描述。采用了一种基于扩散理论的新方法，该方法无需恒场、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，并证明了戈德曼系数只是在这些限制适用时才有用的一种特殊情况。渗透率可直接从电流-电压数据中评估得出，结果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，它就与浓度无关了。因此，可以从这些数据中确定该和，在这个通道中其值为 -65 mV。该电位下的渗透率是一个通道参数，对于这个通道等于8.66×10⁻⁶ cm/s。结果表明这个通道中不存在恒场，且戈德曼系数不是一个参数，而是电位和浓度的函数。尽管非恒场和不相等表面电位给该系数带来的误差部分相互抵消，但该系数仍然不是渗透率的正确度量。
