Activation and inactivation of homomeric KvLQT1 potassium channels
Activation and inactivation of homomeric KvLQT1 potassium channels
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DOI：
10.1016/s0006-3495(98)77568-x
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发表时间：
1998-08-01
影响因子：
3.4
通讯作者：
Conti, F
中科院分区：
文献类型：
--
作者：
Pusch, M;Magrassi, R;Conti, F
电压门控钾通道蛋白 KvLQT1（Wang 等人，1996，Nature Genet. 12:17-23）被认为是心肌延迟整流钾电流的基础，与小膜蛋白 minK（也称为 IsK）一起作为重要的辅助亚基（Barhanin 等人，1996. Nature. 384:78-80；Sanguinetti 等人） 等，1996。《自然》。 384，80-83）。使用非洲爪蟾卵母细胞表达系统，我们使用两电极电压钳记录详细分析了同聚 KvLQT1 通道和异聚 KvLQT1/minK 通道的门控特征。同聚 KvLQT1 在正电压下的激活伴随着失活过程，该过程通过膜复极化至负值后电导的瞬时增加来揭示。我们研究了在不同幅度和持续时间的调节脉冲后，在-120 mV 的尾部复极化期间从失活中恢复和失活的通道。大多数测量是在高细胞外钾条件下进行的，以增加向内尾电流的大小。然而，在正常低钾溶液中进行的实验表明，与经典的 C 型失活相反，KvLQT1 的失活不依赖于细胞外钾。在 +40 mV 时，延迟 100 ms 发生失活。在相同电势下，根据尾电流后期指数衰减幅度估计的激活遵循较小的 S 形时间过程，后期时间常数为 300 ms。即使在最正电压下，KvLQT1 的失活也不完全。延迟的电压依赖性起始和失活的不完全性表明顺序门控方案包含至少两个开放状态并以与电压无关的失活步骤结束。在 KvLQT1 与 minK 的共表达实验中，尽管也观察到可能与类似现象相关的双相尾部，但似乎基本上不存在失活。
The voltage-gated potassium channel protein KvLQT1 (Wang et al., 1996, Nature Genet. 12:17-23) is believed to underlie the delayed rectifier potassium current of cardiac muscle together with the small membrane protein minK (also named IsK) as an essential auxiliary subunit (Barhanin et at., 1996. Nature. 384:78-80; Sanguinetti et al., 1996. Nature. 384,80-83). Using the Xenopus oocyte expression system, we analyzed in detail the gating characteristics of homomeric KvLQT1 channels and of heteromeric KvLQT1/minK channels using two-electrode voltage-clamp recordings. Activation of homomeric KvLQT1 at positive voltages is accompanied by an inactivation process that is revealed by a transient increase in conductance after membrane repolarization to negative values. We studied the recovery from inactivation and the deactivation of the channels during tail repolarizations at -120 mV after conditioning pulses of variable amplitude and duration. Most measurements were made in high extracellular potassium to increase the size of inward tail currents. However, experiments in normal low-potassium solutions st-cowed that, in contrast to classical C-type inactivation, the inactivation of KvLQT1 is independent of extracellular potassium. At +40 mV inactivation develops with a delay of 100 ms. At the same potential, the activation estimated from the amplitude of the late exponential decay of the tail currents follows a less sigmoidal time course, with a late time constant of 300 ms. Inactivation of KvLQT1 is not complete, even at the most positive voltages. The delayed, voltage-dependent onset and the incompleteness of inactivation suggest a sequential gating scheme containing at least two open states and ending with an inactivating step that is voltage independent. In coexpression experiments of KvLQT1 with minK, inactivation seems to be largely absent, although biphasic tails are also observed that could be related to similar phenomena.