Lacombe B, Thibaud J B
Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, UM2/INRA/Agro-M/CNRS URA 2133, Place Viala, 34060 Montpellier cedex 1, France.
J Membr Biol. 1998 Nov 15;166(2):91-100. doi: 10.1007/s002329900451.
KAT1 is a cloned voltage-gated K+ channel from the plant Arabidopsis thaliana L., which displays an inward rectification reminiscent of 'anomalous' rectification of the if pacemaker current recorded in animal cells. Macroscopic conductance of KAT1 expressed in Xenopus oocytes was 5-fold less in pure Rb+ solution than in pure K+ solution, and negligible in pure Na+ solution. Experiments in different K+/Na+ or K+/Rb+ mixtures revealed deviations from the principle of independence and notably two anomalous effects of the K+/Rb+ mole fraction (i.e., the ratio [K+]/([K+]+[Rb+])). First, the KAT1 deactivation time constant was both voltage- and mole fraction-dependent (a so-called 'foot in the door' effect was thus observed in KAT1 channel). Second, when plotted against the K+/Rb+ mole fraction, KAT1 conductance values passed through a minimum. This minimum is more important for two pore mutants of KAT1 (T259S and T260S) that displayed an increase in PRb/PK. These results are consistent with the idea that KAT1 conduction requires several ions to be present simultaneously within the pore. Therefore, this atypical 'green' member of the Shaker superfamily of K+ channels further shows itself to be an interesting model as well for permeation as for gating mechanism studies.
KAT1是从植物拟南芥中克隆出的一种电压门控钾离子通道，其呈现内向整流特性，类似于在动物细胞中记录到的If起搏电流的“异常”整流。在非洲爪蟾卵母细胞中表达的KAT1，在纯铷离子溶液中的宏观电导率比在纯钾离子溶液中低5倍，而在纯钠离子溶液中可忽略不计。在不同的钾离子/钠离子或钾离子/铷离子混合物中的实验揭示了与独立性原则的偏差，特别是钾离子/铷离子摩尔分数（即[K⁺]/([K⁺]+[Rb⁺])）的两种异常效应。首先，KAT1失活时间常数既依赖于电压也依赖于摩尔分数（因此在KAT1通道中观察到了所谓的“入门”效应）。其次，当以钾离子/铷离子摩尔分数作图时，KAT1电导率值会经过一个最小值。对于KAT1的两个双孔突变体（T259S和T260S），这个最小值更为重要，它们表现出PRb/PK的增加。这些结果与KAT1传导需要几个离子同时存在于孔内的观点一致。因此，钾离子通道Shaker超家族的这个非典型“绿色”成员，在渗透研究和门控机制研究方面，进一步证明自身是一个有趣的模型。
