White M M, Miller C
J Gen Physiol. 1981 Jul;78(1):1-18. doi: 10.1085/jgp.78.1.1.
The open-channel conductance properties of a voltage-gated Cl- channel derived from Torpedo californica electroplax and incorporated into planar bilayers were studied by several approaches. In neutral bilayers the channel conductance saturates with Cl- activity according to a rectangular hyperbolic relation with a half-saturation activity of 75 mM and a maximum conductance of 32 pmho. The observation of identical behavior in charged membranes implies that ions permeating the channel do not sense the surface potential of the bulk membrane. The Cl-:Br- permeability ratio, measured under biionic conditions, is independent of salt concentration. SCN- ion reversibly blocks the channel. The voltage dependence of the block implies the existence of two separate blocking sites within the channel: one accessible from the cis side only (the side to which vesicles are added) and the other accessible from the trans side only. The block at each site is competitive with Cl-. The results are consistent with a single-ion Eyring model of the conduction process in which the ion must traverse three kinetic barriers as it permeates the channel and in which the channel can accommodate at most one ion at a time.
通过多种方法研究了从加州电鳐电板中提取并整合到平面双层膜中的电压门控氯离子通道的开放通道电导特性。在中性双层膜中，通道电导根据矩形双曲线关系随氯离子活性饱和，半饱和活性为75 mM，最大电导为32 pS。在带电膜中观察到相同行为，这意味着透过通道的离子不会感知本体膜的表面电位。在双离子条件下测量的氯离子与溴离子的渗透率比值与盐浓度无关。硫氰酸根离子可逆地阻断该通道。阻断的电压依赖性意味着通道内存在两个独立的阻断位点：一个仅从顺式侧（添加囊泡的一侧）可及，另一个仅从反式侧可及。每个位点的阻断与氯离子具有竞争性。这些结果与单离子艾林传导模型一致，在该模型中，离子在透过通道时必须穿越三个动力学屏障，且通道一次最多可容纳一个离子。
