Cope F W
Physiol Chem Phys. 1977;9(4-5):389-98.
If, as recent evidence indicates, most cell potassium is associated with macromolecular fixed charge, then diffusion of potassium ions in cells might occur by (1) diffusion of the small fraction of free potassium in cell water (analogous to electrons in the conduction band of a semiconductor) or by (2) diffusion of vacancies on association sites (analogous to holes in a semiconductor). Derivations of the Fick first law of diffusion predict that partial substitution of sodium for potassium in the cell produces opposite effects on the effective diffusion constant of potassium for those mechanisms. Application of that substitution to nerve data suggests that rubidium ions diffuse by a free cation result when the nerve is clamped at its resting potential, but by a vacancy mechanism when the nerve is clamped at zero voltage.
如果正如最近的证据所表明的，大多数细胞内的钾与大分子固定电荷相关联，那么细胞内钾离子的扩散可能通过以下两种方式发生：（1）细胞内水中一小部分游离钾的扩散（类似于半导体导带中的电子），或者（2）结合位点上空位的扩散（类似于半导体中的空穴）。扩散的菲克第一定律的推导预测，细胞内钠对钾的部分替代会对这两种机制下钾的有效扩散常数产生相反的影响。将这种替代应用于神经数据表明，当神经钳制在静息电位时，铷离子通过自由阳离子机制扩散，而当神经钳制在零电压时，则通过空位机制扩散。
