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Molecular Mechanism of QT Prolongation due to dysfunction of HERG K^+ Channels

HERG K^通道功能障碍导致QT延长的分子机制

基本信息

批准号：
10470161
负责人：
HIRAOKA Masayasu
金额：
$ 9.66万
依托单位：
Tokyo Meducal and Dental University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

项目摘要

HERG encodes Ikr current, an important factor for cardiac repolarization and gene defects in HERG cause one form of inherited long QT syndrome (LQT2). HERG/Ikr currents are the targets of various cardiac and non-cardiac drugs that causes drug-induced long QT syndrome. We studied molecular mechanism of HERG current suppression in gene defects found in LQT2 families and by factors known to block Ikr currents. Functional abnormality ofHERG mutations in T474I, A614V and V630L were analyzed using heterologous expression system in Xenopus oocytes. The mutant alone could not express current, but co-injection with wild type and each mutant produced dominant negative suppression (DNS) with its degree increasing in the order of V63OL>A614V>T474I.V60L and A614V further produced negative shift in steady state inactivation curve and fastened inactivation. We next analyzed R534C mutation in S4, presumed voltage sensor. R534C shifted voltage-dependent activation confirming S4 playing as voltage sensor, and produced fast deactivation. But, fast deactivation could not explain the reason for QT prolongation in R534C, suggesting the presence of another unknown factor. The mutation in HERG C-terminus, S818L, did not express the current by mutant alone and co-injection with wild type did not show DNS.However co-injection of wild type and excess amount of cRNA of S818L produced DNS and shifted activation curve with fast activation and deactivation kinetics. The results suggest that S818L can form heteromultimer with wild type to yield functional channels with wild type, and that the C-terminus of HERG may participate in activation process of this channels. Therefore, various types and locations of HERG mutaions cause current suppression with different mechanisms. We also explored acidosis-induced suppression of HERG current due mainly to effects on activation process.

HERG编码Ikr电流，Ikr电流是心脏复极的重要因素，HERG中的基因缺陷导致一种形式的遗传性长QT综合征（LQT 2）。HERG/Ikr电流是导致药物诱导的长QT综合征的各种心脏和非心脏药物的靶点。我们研究了在LQT 2家族中发现的基因缺陷中HERG电流抑制的分子机制，以及已知阻断Ikr电流的因素。利用爪蟾卵母细胞异源表达系统分析了T474 I、A614 V和V630 L三个HERG突变的功能异常。突变体单独不能表达电流，但与野生型共注射后，各突变体均产生显性负性抑制（DNS），其抑制程度依次为V63 OL> A614 V> T474 I，V60 L和A614 V进一步使稳态失活曲线负移，并加速失活。我们接下来分析了S4中的R534 C突变，推测为电压传感器。R534 C转移了电压依赖性激活，确认S4作为电压传感器，并产生快速失活。但是，快速失活不能解释R534 C QT间期延长的原因，这表明存在另一个未知因素。HERG C端突变体S818 L单独注射时不表达电流，与野生型共注射时不表达DNS，而野生型与过量S818 L cRNA共注射时产生DNS，使激活曲线移动，激活和失活动力学快速。结果表明，S818 L与野生型形成异源多聚体，形成具有野生型功能的通道，HERG的C端可能参与了该通道的激活过程。因此，不同类型和位置的HERG突变以不同的机制引起电流抑制。我们还探讨了酸中毒引起的HERG电流抑制，主要是由于激活过程的影响。