Heginbotham L, MacKinnon R
Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
Biophys J. 1993 Nov;65(5):2089-96. doi: 10.1016/S0006-3495(93)81244-X.
The conduction properties of the cloned Shaker K+ channel were studied using electrophysiological techniques. Single channel conductance increases in a sublinear manner with symmetric increases in K+ activity, reaching saturation by 0.6 M K+. The Shaker K+ channel is highly selective among monovalent cations; under bi-ionic conditions, its selectivity sequence is K+ > Rb+ > NH+4 > Cs+ > Na+, whereas, by relative conductance in symmetric solutions, it is K+ > NH+4 > Rb+ > Cs+. In Cs+ solutions, single channel currents were too small to be measured directly, so nonstationary fluctuation analysis was used to determine the unitary Cs+ conductance. The single channel conductance displays an anomalous molefraction effect in symmetric mixtures of K+ and NH+4, suggesting that the conducting pore is occupied by multiple ions simultaneously.
利用电生理技术研究了克隆的Shaker钾通道的传导特性。单通道电导随钾离子活性对称增加而呈亚线性增加，在0.6M钾离子时达到饱和。Shaker钾通道在单价阳离子中具有高度选择性；在双离子条件下，其选择性顺序为K+ > Rb+ > NH4+ > Cs+ > Na+，而在对称溶液中按相对电导排序为K+ > NH4+ > Rb+ > Cs+。在铯离子溶液中，单通道电流太小无法直接测量，因此采用非平稳波动分析来确定单一铯离子电导。单通道电导在钾离子和铵根离子的对称混合物中表现出异常摩尔分数效应，表明导电孔道同时被多个离子占据。
