Hanke W, Miller C
J Gen Physiol. 1983 Jul;82(1):25-45. doi: 10.1085/jgp.82.1.25.
Single-channel fluctuations of a chloride-specific channel from Torpedo californica electroplax were studied with high current and time resolution. Channels were incorporated into virtually solvent-free planar bilayer membranes formed from phospholipid monolayers, and the substructure of the open channel was analyzed. The single channel displays three well-defined substates of conductances 0, 10, and 20 pS in 200 mM Cl-. These three substates are interpreted in terms of a dimeric channel complex composed of two identical "protochannels" gating independently in parallel on a time scale of milliseconds, but coupled together by a bursting process on a time scale of seconds. The probability of forming an open protochannel is voltage dependent and is increased strongly as aqueous pH is lowered. Variations of pH are effective only on the same side of the bilayer as the addition of electroplax vesicles. The dependence of single-channel kinetics on pH and voltage lead to a minimal four-state model in which both open and closed states can be protonated on a residue that changes its pK from 6 to 9 upon opening of the protochannel.
利用高电流和高时间分辨率研究了来自加州电鳐电板的氯离子特异性通道的单通道波动情况。将通道整合到由磷脂单分子层形成的几乎无溶剂的平面双层膜中，并对开放通道的亚结构进行了分析。在200 mM Cl- 中，单通道表现出三种明确的电导亚态，分别为0、10和20 pS。这三种亚态被解释为一种二聚体通道复合物，它由两个相同的“原通道”组成，在毫秒时间尺度上独立并行门控，但在秒时间尺度上通过爆发过程耦合在一起。形成开放原通道的概率取决于电压，并且随着水溶液pH值的降低而显著增加。pH值的变化仅在双层膜与添加电板囊泡同侧时才有效。单通道动力学对pH值和电压的依赖性导致了一个最小的四态模型，其中开放态和关闭态都可以在一个残基上被质子化，该残基在原通道打开时其pK值从6变为9。
