Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (UA), Universiteitsplein 1, 2610 Antwerp, Belgium.
J Mol Cell Cardiol. 2010 Jun;48(6):1096-104. doi: 10.1016/j.yjmcc.2009.10.027. Epub 2009 Nov 11.
The long QT syndrome (LQTS) is a cardiac disorder caused by a prolonged ventricular repolarization. The co-assembly of the pore-forming human KCNQ1 alpha-subunits with the modulating hKCNE1 beta-subunits generates I(Ks)in vivo, explaining why mutations in the hKCNQ1 gene underlie the LQT1 form of congenital LQT. Here we describe the functional defects of the LQT1 mutation H258R located in the S4-S5 linker, a segment important for channel gating. Mutant subunits with this arginine substitution generated no or barely detectable currents in a homotetrameric condition, but did generate I(Ks)-like currents in association with hKCNE1. Compared to the WT hKCNQ1/hKCNE1 complex, the H258R/hKCNE1 complex displayed accelerated activation kinetics, slowed channel closure and a hyperpolarizing shift of the voltage-dependence of activation, thus predicting an increased K(+) current. However, current density analysis combined with subcellular localization indicated that the H258R subunit exerted a dominant negative effect on channel trafficking to the plasma membrane. The co-expression hKCNQ1/H258R/hKCNE1, mimicking the heterozygous state of a patient, displayed similar properties. During repetitive stimulation the mutant yielded more current compared to WT at 1 Hz but this effect was counteracted by the trafficking defect at faster frequencies. These rate-dependent effects may be relevant given the larger contribution of I(Ks) to the "repolarization reserve" at higher action potential rates. The combination of complex kinetics that counteract the trafficking problem represents a particular mechanism underlying LQT1.
长 QT 综合征（LQTS）是一种由心室复极延长引起的心脏疾病。孔形成人 KCNQ1α-亚基与调节 hKCNE1β-亚基的共组装在体内产生 I(Ks)，这解释了为什么 hKCNQ1 基因的突变是先天性 LQT 的 LQT1 形式的基础。在这里，我们描述了位于 S4-S5 连接段的 LQT1 突变 H258R 的功能缺陷，该连接段对于通道门控很重要。具有这种精氨酸取代的突变亚基在四聚体条件下几乎不能产生或检测到电流，但与 hKCNE1 结合时会产生 I(Ks)样电流。与 WT hKCNQ1/hKCNE1 复合物相比，H258R/hKCNE1 复合物显示出加速的激活动力学、通道关闭减慢以及激活的电压依赖性超极化移位，从而预测 K(+)电流增加。然而，电流密度分析结合亚细胞定位表明，H258R 亚基对通道向质膜的转运具有显性负效应。模拟患者杂合状态的共表达 hKCNQ1/H258R/hKCNE1 显示出相似的特性。在重复刺激期间，与 WT 相比，突变体在 1 Hz 时产生更多的电流，但这种效应被转运缺陷在更快的频率下抵消。鉴于 I(Ks)在更高动作电位率下对“复极储备”的贡献更大，这些速率依赖性效应可能是相关的。抵消转运问题的复杂动力学组合代表了 LQT1 的一种特殊机制。
