IONIC SELECTIVITY, SATURATION AND BLOCK IN GRAMICIDIN-A CHANNELS - .1. THEORY FOR ELECTRICAL-PROPERTIES OF ION-SELECTIVE CHANNELS HAVING 2 PAIRS OF BINDING-SITES AND MULTIPLE CONDUCTANCE STATES
IONIC SELECTIVITY, SATURATION AND BLOCK IN GRAMICIDIN-A CHANNELS - .1. THEORY FOR ELECTRICAL-PROPERTIES OF ION-SELECTIVE CHANNELS HAVING 2 PAIRS OF BINDING-SITES AND MULTIPLE CONDUCTANCE STATES
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DOI：
10.1007/bf01869414
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发表时间：
1977-01-01
影响因子：
2.4
通讯作者：
NEHER, E
中科院分区：
文献类型：
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作者：
SANDBLOM, J;EISENMAN, G;NEHER, E
通过在通道的每个入口处增加一个特定的阳离子结合位点来扩展已有的模型，提出了一个针对gallicidin A通道的模型。离子与这些外部通道位置的结合被认为移动了内部位置和势垒的能级，从而改变了通道电导。对于最简单的两个内位和一个能垒的情况，从理论上分析了得到的性质。这个四点模型(两个外部和两个内部)预测，零电流下的膜电位(U0)应该由浓度依赖的渗透率比的Goldman-Hodgkin-Katz方程来描述。结果表明，浓度相关项的系数与势垒的峰值能量位移和外位的结合常数有关。该理论还预测了对称解中的沟道电导表现出3种极限行为，由此可以表征外位和内位的性质。在2-阳离子对称混合物中，电导随摩尔分数的变化有一极小值，并用理论解释了1-离子对另一种离子的抑制和堵塞现象。这些不同的现象，以多占据通道中的离子相互作用为共同的物理基础，都通过一组描述系统性质的可测量参数来关联(通过理论)。
A model for the gramicidin A channel is proposed which extends existing models by adding a specific cationic binding site at each entrance to the channel. The binding of ions to these outer channel sites is assumed to shift the energy levels of the inner sites and barriers and thereby alter the channel conductance. The resulting properties are analyzed theoretically for the simplest case of 2 inner sites and a single energy barrier. This 4-site model (2 outer and 2 inner) predicts that the membrane potential at zero current (U0) should be described by a Goldman-Hodgkin-Katz equation with concentration-dependent permeability ratios. The coefficients of the concentration-dependent terms are shown to be related to the peak energy shifts of the barrier and to the binding constants of the outer sites. The theory also predicts the channel conductance in symmetrical solutions to exhibit 3 limiting behaviors, from which the properties of the outer and inner sites can be characterized. In 2-cation symmetrical mixtures the conductance as a function of mol fraction is shown to have a minimum, and the related phenomenon of inhibition and block exerted by 1 ion on the other is explained explicitly by the theory. These various phenomena, having ion interactions in a multiply occupied channel as a common physical basis, are all related (by the theory) through a set of measurable parameters describing the properties of the system.