Cardiac Ion Channel Regulation

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DESCRIPTION (provided by applicant): Cardiac excitability is finely controlled by a combination of depolarizing and repolarizing currents. Fine regulation and dysregulation of a host of inward and outward ion currents are thought to play a major role in numerous clinically relevant cardiac arrhythmias. In fact, it is now well established that even subtle alterations of the cardiac action potential properties caused by dysfunction of ion channels, may lead to cardiac disorders known as channelopathies. Classic formalism teaches that ion channels function independently of each other according to their individual time- and voltage- dependent biophysical properties. This is the basis for computer models developed to understand single cell electrophysiological behavior. However, in Brugada syndrome (BrS), a form of genetic arrhythmia caused by mutations in the sodium channel, functional interaction between channels mediating potassium (Ito) and sodium (INa) currents has been suggested to be involved in the two main arrhythmogenic mechanisms: repolarization disorder and conduction disorder hypothesis. Thus, is it possible that the regulation of ion channel subunits mediating these two major currents of the cardiac action potential is coordinated? Notably, our recent work was the first to support this provocative idea that the expression of the depolarizing sodium channel and the repolarizing potassium channel Ito may share a common, yet to be identified, regulatory mechanism. Following gene silencing of KChIP2, an accessory subunit of Ito, the applicant found that the expression of Ito and INa was abolished producing a non-excitable cardiac myocytes. This suggested that the regulation of ion channel mediating these two major currents could be coordinated. This would represent a paradigm-shifting concept regarding ion channels expression and regulation. Therefore, we hypothesize that KChIP2 controls the expression of depolarizing (INa) and repolarizing (Ito) currents through multiple regulatory mechanisms. The specific aims of this proposal are to: 1. Identify genes modulated by KChIP2. 2. Determine if the regulation of INa and Ito involves microRNA(s). 3. Define the role of KChIP2 miRNA-dependent regulation in cardiac pathology. The delineation of the molecular basis of this regulation is essential for an accurate understanding of cardiac ventricular depolarization and repolarization and its derangements that are associated with lethal ventricular arrhythmias. Further functional dissection of KChIP2 will provide insight into numerous aspects of cardiac function will illuminate the role of the KChIP2 family of proteins in disease and likely unveil novel paradigms for ion channel function in health and disease. PUBLIC HEALTH RELEVANCE: This project will provide new critical insights into the functional association and regulation of ionic currents that are essential to normal depolarization and repolarization in the heart. Understanding the mechanisms of regulation of sodium and potassium currents will contribute to our understanding of their involvement in diseased states.