Molecular basis and proarrhythmic role of enhanced small conductance Ca2+ activated K+ channels in patients with atrial fibrillation

心房颤动(房颤)是一种常见的心律失常，发病率和死亡率均呈上升趋势。目前的抗心律失常药物疗效不佳，可能存在严重的不良反应。显然有必要为房颤治疗确定新的房室选择靶点，因为这会产生较少的不良心脏效应。尽管心房选择性小电导钙激活钾通道(SK通道)已成为抗房颤治疗的潜在靶点，但其在人心房房颤发生机制中的确切作用和具体作用尚不清楚。潜在增加的SK通道电流(ISK)在房性心律失常发生中的作用是复杂的。它可能通过缩短动作电位时程而有利于重返大气层，但也可以通过减少自律性/通过膜超极化/降低兴奋性来减少触发活动来抗心律失常。基于我们先前强调房颤相关钙处理异常的中心作用以及我们对房颤患者ISK异常的初步研究，我们假设增强的ISK在钙依赖的触发活动(SR钙泄漏)和折返(更短的时程)之间提供了联系，在支持房颤维持的心律失常底物的形成中发挥了关键作用。因此，本研究的主要目的是发现和剖析房颤患者ISK增强的细胞和分子机制，并阐明ISK在房颤患者时程缩短和心律失常机制中的确切作用。作为第一步，我们将利用分子生物学技术验证SK通道异构体及其调控蛋白的表达，鉴定SK通道运输的细胞和分子决定因素，并建立SK通道复杂组织和局部调节的潜在异常，这些异常可能改变房颤患者钙依赖的通道门控。然后，我们将从功能上评估ISK的钙浓度反应关系，包括钙内流和内部钙释放的贡献，探索不同的基于肌动蛋白和微管驱动的转运途径的作用，并测试房颤相关房率对房颤患者ISK调节的影响。最后，我们将提炼ISK对人类心房AP的作用，并剖析药物ISK调节对房颤患者的前心律失常(通过引起时程缩短对折返底物的贡献)和抗心律失常(对抗后除极介导的局灶性异位[触发]活动)后果。结合拟议的实验，将提供对ISK决定因素、它们在房颤中的重塑和调节的分子和功能方面的见解。最终，这项工作的洞察力应该有助于确定房颤患者的新治疗靶点。

Atrial fibrillation (AF) is a frequent arrhythmia increasing morbidity and mortality. Current antiarrhythmic drugs have suboptimal efficacy and potentially severe adverse effects. There is a clear need for the identification of new atrial selective targets for AF therapy, since this produces less unwanted ventricular effects. Although atrial selective small conductance Ca2+ activated K+ channels (SK channels) have emerged as a potential target for anti AF therapy, their precise function and specific contribution to AF mechanisms in the human atrium is not established. The role of potentially increased SK channel current (ISK) in atrial arrhythmogenesis is complex. It might favour reentry by abbreviating action potential duration (APD), but can also be antiarrhythmic by reducing automaticity/triggered activity through membrane hyperpolarization/reduced excitability. Based on our previous work highlighting a central role for AF related Ca2+ handling abnormalities in atrial cardiomyocytes and our preliminary work on ISK dysregulation in AF patients, we hypothesize that enhanced ISK provides a link between Ca2+ dependent triggered activity (SR Ca2+ leak) and reentry (shorter APD), playing a critical role in the formation of the proarrhythmic substrate supporting AF maintenance. Therefore, the primary goal of this application is to discover and dissect the cellular and molecular mechanisms of enhanced ISK in AF and to delineate the precise contributions of ISK to APD shortening and arrhythmia mechanisms in AF patients. As an initial step we will exploit molecular biology techniques to validate the expression of SK channel isoforms and their regulatory proteins, identify the cellular and molecular determinants of SK channel trafficking and establish potential abnormalities in the complex organization and local regulation of SK channels that could alter Ca2+ dependent channel gating in AF patients. Then we will functionally assess the Ca2+ concentration response relationship of ISK including contribution of Ca2+ influx vs. internal Ca2+ release, explore the role of different actin based and microtubule driven trafficking pathways and test the effects of AF relevant atrial rates on the regulation of ISK in AF patients. Finally we will refine the contribution of ISK to human atrial AP and dissect the proarrhythmic (contribution to the reentrant substrate by causing APD shortening) and anti arrhythmic (protection against afterdepolarization mediated focal ectopic [triggered] activity) consequences of pharmacological ISK modulation in AF patients. Combined the proposed experiments will provide molecular and functional insights into the ISK determinants, their remodeling and regulation in AF. Ultimately, the insights from this work should facilitate the identification of novel therapeutic targets in AF patients.