Pusch M, Magrassi R, Wollnik B, Conti F
Istituto di Cibernetica e Biofisica, CNR, I-16149 Genoa, Italy.
Biophys J. 1998 Aug;75(2):785-92. doi: 10.1016/S0006-3495(98)77568-X.
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 al., 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 showed 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.
电压门控钾通道蛋白KvLQT1（Wang等人，1996年。《自然遗传学》12:17 - 23）被认为与小膜蛋白minK（也称为IsK）一起构成心肌延迟整流钾电流的基础，minK是一种重要的辅助亚基（Barhanin等人，1996年。《自然》384:78 - 80；Sanguinetti等人，1996年。《自然》384:80 - 83）。利用非洲爪蟾卵母细胞表达系统，我们使用双电极电压钳记录详细分析了同聚体KvLQT1通道和异聚体KvLQT1/minK通道的门控特性。同聚体KvLQT1在正电压下的激活伴随着一个失活过程，该过程通过膜复极化到负值后电导的短暂增加而显现。我们研究了在不同幅度和持续时间的预处理脉冲后，在 - 120 mV的尾电流复极化过程中通道从失活状态的恢复以及去激活情况。大多数测量是在高细胞外钾浓度下进行的，以增加内向尾电流的大小。然而，在正常低钾溶液中的实验表明，与经典的C型失活不同，KvLQT1的失活与细胞外钾无关。在 + 40 mV时，失活延迟100毫秒出现。在相同电位下，根据尾电流后期指数衰减的幅度估计的激活遵循不太呈S形的时间进程，后期时间常数为300毫秒。即使在最正的电压下，KvLQT1的失活也不完全。延迟的、电压依赖性的起始以及失活的不完全性表明了一种顺序门控机制，该机制至少包含两个开放状态，并以一个与电压无关的失活步骤结束。在KvLQT1与minK的共表达实验中，失活似乎基本不存在，尽管也观察到了双相尾电流，这可能与类似现象有关。
