Wu J V
Department of Physiology, University of Rochester Medical Center, New York 14642-8642.
Biophys J. 1992 May;61(5):1316-31. doi: 10.1016/S0006-3495(92)81940-9.
The dynamic interactions among ions and water molecules in ion channels are treated based on an assumption that ions at binding sites can be knocked off by both transient entering ions and local water molecules. The theory, when applied to a single-site model K+ channel, provides solutions for super- and subsaturations, flux-ratio exponent (n') greater than 1, osmotic streaming current, activity-dependent reversal potentials, and anomalous mole-fraction behavior. The analysis predicts that: (a) the saturation may but, in general, does not follow the Michaelis-Menten relation; (b) streaming current results from imbalanced water-ion knock-off interactions; (c) n' greater than 1 even for single-site channels, but it is unlikely to exceed 1.4 unless the pore is occupied by one or more ion(s); (d) in the calculation involving two permeant ion species with similar radii, the heavier ions show higher affinity; the ion-ion knock-off dissociation from the site is more effective when two interacting ions are identical. Therefore, the "multi-ion behaviors" found in most ion channels are the consequences of dynamic ion-ion and water-ion interactions. The presence of these interactions does not require two or more binding sites in channels.
基于结合位点处的离子可被瞬时进入的离子和局部水分子撞离的假设，对离子通道中离子与水分子之间的动态相互作用进行了处理。该理论应用于单位点模型钾离子通道时，给出了超饱和与亚饱和、通量比指数（n'）大于1、渗透流电流、活性依赖的反转电位以及异常摩尔分数行为的解决方案。分析预测：（a）饱和度可能遵循但通常不遵循米氏关系；（b）流电流源于水 - 离子撞离相互作用的不平衡；（c）即使对于单位点通道，n'也大于1，但除非孔被一个或多个离子占据，否则不太可能超过1.4；（d）在涉及两种半径相似的渗透离子物种的计算中，较重的离子显示出更高的亲和力；当两个相互作用的离子相同时，离子 - 离子从位点的撞离解离更有效。因此，大多数离子通道中发现的“多离子行为”是动态离子 - 离子和水 - 离子相互作用的结果。这些相互作用的存在并不要求通道中有两个或更多的结合位点。
