POST INFARCTION K CHANNEL REMODELING/MOLECULAR MECHANISM

我们研究项目的长期目标是了解正常心脏中K通道功能异质性的分子基础，以及患病心脏中K通道功能改变的机制。在正常心脏中，K通道的非均质性有助于维持心脏电稳定性。这种正常异质性的扰动可能使心脏易发生心律失常。这种情况发生在肥厚/衰竭的心脏，其中K通道功能的改变有助于复极的分散，为再入性心律失常奠定了基础。为了设计针对这些病理条件的有效疗法，重要的是要知道，在分子水平上，是什么导致了这种正常的K通道分布模式，以及它是如何在患病的心脏中受到干扰的。本研究的重点是心肌细胞内三种主要的复极K电流，即瞬时外向（Ito）、慢延迟整流（IKs）和快速延迟整流（IKr）电流。我们将以狗作为我们的动物模型，比较正常心脏和发生各种重塑过程的慢性心肌梗死心脏的K通道功能。我们将应用电生理学、分子生物学、免疫印迹和免疫细胞化学技术来检测通道功能和亚基表达。该策略是在心肌细胞的天然通道实验和体外系统中表达的通道克隆实验之间使用迭代过程，以建立亚基组成和通道功能之间的相关性。提出了四个具体目标。在前3个目标下，我们将研究为什么Ito， IKs和IKr的电流密度和门控动力学在正常心脏中分别是不均匀的。这些信息以及我们在这些Aims中开发的工具（K通道亚基cdna和抗体）将在Aim 4中应用，以检查梗死后心脏K通道重塑的分子基础。这些实验结果将为心脏K通道的分子生理学和病理学提供新的见解，这将有助于梗死后重构心脏心律失常的治疗干预设计。

The long-long objectives of our research project are to understand the molecular basis for heterogeneity in K channel function in normal heart, and the mechanisms for alterations in K channel function in diseased heart. In normal heart, the pattern of K channel heterogeneity helps maintain the cardiac electrical stability. Perturbations of such normal heterogeneity will likely predispose the heart to arrhythmias. Such situation occurs in hypertrophied/failing hearts where alterations in K channel function contribute to a dispersion of repolarization, setting the stage for reentrant arrhythmias. To design effective therapies for these pathological conditions, it is important to know, at the molecular level, what causes such a normal pattern of K channel distribution and how it is perturbed in diseased heart. The focus of this proposal is the transient outward (Ito), slow delayed rectifier (IKs) and rapid delayed rectifier (IKr) currents, the three major repolarizing K currents in cardiac myocytes. We will use dog as our animal model, and compare K channel function in normal hearts and in hearts with chronic myocardial infarction where various remodeling processes have occurred. We will apply the techniques of electrophysiology, molecular biology, immunoblotting and immunocytochemistry to examine channel function and subunit expression. The strategy is to use an iterative process between experiments on native channels in cardiac myocytes and experiments on channel clones expressed in in vitro systems to establish a correlation between subunit composition and channel function. Four Specific Aims are proposed. Under the first 3 Aims, we will study why the current density and gating kinetics of Ito, IKs and IKr, respectively, are heterogeneous in normal heart. The information, as well as the tools (K channel subunit cDNAs and antibodies) we develop during these Aims, will be applied under Aim 4 to examine the molecular basis for K channel remodeling in postinfarction heart. Results from these experiments will provide new insights into molecular physiology and pathology of cardiac K channels, which will aid the design of therapeutic interventions for arrhythmias in postinfarction remodeled hearts.