Molecular Physiology of HERG (KCNH2) Pottasium Channels

描述（由申请人提供）：人ether a go-go相关基因1a（HERG 1a，Kv11.1）K+通道在维持基本心律方面发挥关键作用。HERG 1a通道的重要性在于它是心脏快速延迟整流钾通道（IKr）的中心成分。HERG和IKr专门传导外向K+电流，驱动心脏动作电位晚期的复极化。HERG 1a在健康和疾病中的关键作用通过编码HERG通道的基因中的遗传突变来强调。HERG的突变与长QT综合征（LQTS）有关，这是一种导致心律失常、晕厥和猝死的心脏疾病。HERG通道具有额外的重要性，因为越来越多的药物的副作用是通过抑制HERG通道的功能产生获得性形式的LQTS（aLQTS）。HERG和IKr通道的打开和关闭（门控）对于正常心脏电生理和正常心跳至关重要。特别是，天然IKr通道的关闭速率对于复极化期间外向IKr电流的完美定时至关重要。一些进展，包括我们以前的工作，已经描绘了通道关闭（失活）机制的关键分子组成部分，包括HERG 1a N-末端区域内的两个关键结构域。这些是“PAS”结构域和一个短的上游区域，这里称为PAS-CAP。失活机制的多样性来自HERG 1a变体HERG 1b，它缺乏关键的PAS和PAS-CAP结构域，因此比HERG 1a关闭得更快。心脏中HERG 1b的存在可以解释IKr的失活动力学更快。尽管有这些进展，但通道失活的机制仍然难以捉摸。拟议实验的目标是确定HERG和IKr关闭的综合分子机制。具体目的是：1）检验PAS-CAP区通过与通道的静电相互作用决定失活门控的假设; 2）检验PAS结构域的疏水表面与通道中的疏水性“PAS受体位点”相互作用介导失活的假设; 3）为了检验HERG 1b亚基是天然IKr的关键功能组分以及ERG 1b解释了天然IKr所描述的更快动力学的假设。为了实现具体目标，我们将使用多学科的方法，包括膜片钳和电压钳电生理学在异源表达系统和天然细胞，荧光光谱，基因转移到肌细胞和天然细胞培养技术。我们的长期目标是确定心脏IKr通道门控和调节的基本分子基础，以更好地治疗遗传性LQTS和预防获得性LQTS。

DESCRIPTION (provided by applicant): Human ether a go-go-related gene 1a (HERG1a, Kv11.1) K+ channels play a critical role in maintaining the fundamental cardiac rhythm. The significance of HERG1a channels is that they are the central component of the rapid delayed-rectifier K+ channel (IKr) in heart. HERG and IKr are specialized to conduct an outward K+ current that drives repolarization of the late phase of the cardiac action potential. The critical role of HERG1a in health and disease is emphasized by inherited mutations in the gene encoding HERG channels. Mutations in HERG are associated with the long QT syndrome (LQTS) a cardiac disorder that causes arrhythmia, syncope and sudden death. HERG channels are of additional significance as a side-effect of an increasing number of pharmaceuticals is to produce an acquired form of LQTS (aLQTS) by inhibiting the function of HERG channels. The opening and closing (gating) of HERG and IKr channels are critical for normal cardiac electrophysiology and the normal heartbeat. In particular, the closing rate of native IKr channels is vital for the perfect timing of the outward IKr current during repolarization. Some advances, including our previous work, have delineated key molecular components of the channel closing (deactivation) mechanism, including two critical domains within the HERG1a N-terminal region. These are the `PAS' domain and a short region upstream here termed the PAS-CAP. Diversity in the mechanism of deactivation comes from a HERG1a variant, HERG1b that lacks the key PAS and PAS-CAP domains and consequently closes much faster than HERG1a. The presence of HERG1b in heart may explain the faster kinetics of deactivation measured for IKr. Despite these advances, a mechanism for channel deactivation has remained elusive. The goals of the proposed experiments are to determine a comprehensive molecular mechanism for closing in HERG and IKr. The Specific Aims are to 1) test the hypothesis that the PAS-CAP region determines deactivation gating via an electrostatic interaction with the channel 2) to test the hypothesis that the hydrophobic surface of the PAS domain interacts with a hydrophobic `PAS receptor site' in the channel to mediate deactivation and 3) to test the hypothesis that the HERG1b subunit is a key functional component of native IKr and that ERG1b accounts for the faster kinetics described for native IKr. To carry out the specific aims we will use a multidisciplinary approach that includes patch-clamp and voltage-clamp electrophysiology in heterologous expression systems and native cells, fluorescence spectroscopy, gene transfer to myocytes and native cell culture techniques. Our long-term objectives are to determine the fundamental molecular basis of gating and modulation in cardiac IKr channels, in an effort to better treat inherited LQTS and prevent acquired LQTS.