Gillespie Dirk, Eisenberg Robert S
Department of Physiology and Biophysics, University of Miami School of Medicine, P.O. Box 016430, Miami, FL 33101-6430, USA.
Eur Biophys J. 2002 Oct;31(6):454-66. doi: 10.1007/s00249-002-0239-x. Epub 2002 Jul 16.
Three experiments that quantify the amount of selectivity exhibited by a biological ion channel are examined with Poisson-Nernst-Planck (PNP) theory. Conductance ratios and the conductance mole fraction experiments are examined by considering a simple model ion channel for which an approximate solution to the PNP equations with Donnan boundary conditions is derived. A more general result is derived for the Goldman-Hodgkin-Katz permeability ratio. The results show that (1) the conductance ratio measures the ratio of the diffusion coefficients of the ions inside the channel, (2) the mole fraction experiment measures the difference of the excess chemical potentials of the ions inside the channel, and (3) the permeability ratio measures both diffusion coefficients and excess chemical potentials. The results are used to divide selectivity into two components: partitioning, an equilibrium measure of how well the ions enter the channel, and diffusion, a nonequilibrium measure of how well the ions move through the channel.
利用泊松-能斯特-普朗克（PNP）理论研究了三个量化生物离子通道选择性程度的实验。通过考虑一个简单的离子通道模型来研究电导比和电导摩尔分数实验，针对该模型推导出了具有唐南边界条件的PNP方程的近似解。针对戈德曼-霍奇金-卡茨渗透率比得出了一个更通用的结果。结果表明：（1）电导比测量通道内离子扩散系数的比值；（2）摩尔分数实验测量通道内离子过量化学势的差值；（3）渗透率比测量扩散系数和过量化学势。这些结果被用于将选择性分为两个部分：分配，这是离子进入通道程度的平衡度量；扩散，这是离子在通道中移动程度的非平衡度量。
