Gating charge immobilization in Kv4.2 channels: the basis of closed-state inactivation.
Gating charge immobilization in Kv4.2 channels: the basis of closed-state inactivation.
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kv4.2通道中的门控电荷固定：封闭状态失活的基础。
DOI：
10.1085/jgp.200709938
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发表时间：
2008-03
影响因子：
3.8
通讯作者：
Covarrubias, Manuel
中科院分区：
文献类型：
--
作者：
Dougherty, Kevin;De Santiago-Castillo, Jose A.;Covarrubias, Manuel
Kv 4通道介导神经元的体树突A型钾电流（伊萨）。功能性Kv 4通道的可用性由膜电位动态调节，使得阈下去极化使Kv 4通道不可用。潜在的过程涉及从封闭状态沿着主要活化途径的失活。虽然经典的失活机制，如N-和P/C-型失活已被排除，在Kv 4通道的封闭状态失活的清晰理解仍然难以捉摸。这部分是由于缺乏关于门控电荷（Q）移动、激活和失活之间的相互作用的关键信息。为了克服这一限制，我们设计了一种对卡里巴毒素（CTX）敏感的Kv4.2通道，这使我们能够在用CTX阻断K+传导后获得Kv4.2门控电流的第一次测量（DoughnessandCovarrubias. 2006年J。128：745-753）。在这里，我们进一步利用这种方法来研究Kv 4通道中关闭状态失活与缓慢Q固定的机制。主要观察结果显示，在超极化电压范围（−110至−75 mV）内，稳态下存在深刻的Q固定。在此范围内的去极化移动与激活相关的可观察Q的<5%，并且不足以显著打开通道。Q-固定和离子电流失活的动力学和电压依赖性在−153和−47 mV之间是相似的，并且与通道的近端N-末端区域（残基2-40）无关。闭合态失活与准吸收失活态的耦合态图解释了离子电流和门控电流实验的结果。我们的结论是，Q-固定和关闭状态的失活在超极化电压是两个表现形式的Kv4.2通道中的同一过程中，并提出，在N-和P/C-型机制的情况下，失活涉及脱敏电压导致的一个缓慢的构象变化的电压传感器，这使得通道的主要激活门不愿意打开。
Kv4 channels mediate the somatodendritic A-type K+ current (ISA) in neurons. The availability of functional Kv4 channels is dynamically regulated by the membrane potential such that subthreshold depolarizations render Kv4 channels unavailable. The underlying process involves inactivation from closed states along the main activation pathway. Although classical inactivation mechanisms such as N- and P/C-type inactivation have been excluded, a clear understanding of closed-state inactivation in Kv4 channels has remained elusive. This is in part due to the lack of crucial information about the interactions between gating charge (Q) movement, activation, and inactivation. To overcome this limitation, we engineered a charybdotoxin (CTX)-sensitive Kv4.2 channel, which enabled us to obtain the first measurements of Kv4.2 gating currents after blocking K+ conduction with CTX (Dougherty and Covarrubias. 2006J. Gen. Physiol. 128:745–753). Here, we exploited this approach further to investigate the mechanism that links closed-state inactivation to slow Q-immobilization in Kv4 channels. The main observations revealed profound Q-immobilization at steady-state over a range of hyperpolarized voltages (−110 to −75 mV). Depolarization in this range moves <5% of the observable Q associated with activation and is insufficient to open the channels significantly. The kinetics and voltage dependence of Q-immobilization and ionic current inactivation between −153 and −47 mV are similar and independent of the channel's proximal N-terminal region (residues 2–40). A coupled state diagram of closed-state inactivation with a quasi-absorbing inactivated state explained the results from ionic and gating current experiments globally. We conclude that Q-immobilization and closed-state inactivation at hyperpolarized voltages are two manifestations of the same process in Kv4.2 channels, and propose that inactivation in the absence of N- and P/C-type mechanisms involves desensitization to voltage resulting from a slow conformational change of the voltage sensors, which renders the channel's main activation gate reluctant to open.
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