Can Novel Therapies for Arrhythmias Caused by Spontaneous Sarcoplasmic Reticulum Ca 2+ Release be Developed Using Mouse Models?

Abstract

See related article, pages e77–e82 Ventricular arrhythmias are a significant cause of premature death in Western society and occur both in the absence and presence of heart disease. For example, in heart failure close to 50% of patients die of lethal forms of ventricular arrhythmias. In spite of a large amount of basic and clinical investigations, current pharmacotherapy for ventricular arrhythmias is inadequate, demonstrating the need for novel therapeutic approaches. Abnormal automaticity is responsible for induction and maintenance of different types of ventricular tachycardias. The form of abnormal automaticity that results from abnormal release of Ca2+ from a Ca2+ overloaded sarcoplasmic reticulum (SR), referred to as a “triggered arrhythmia”, is the topic of this editorial. In vitro studies have shown that increasing the SR Ca2+ load beyond a critical level causes spontaneous opening of the SR Ca2+ release channel (ryanodine receptor; RYR) and results in spontaneous SR Ca2+ release.1 The subsequent increase in cytosolic [Ca] activates an inward current through the sarcolemmal Na+/ Ca2+ exchanger which causes membrane depolarization.1,2 Spontaneous SR Ca2+ release during the diastolic interval causes depolarization (delayed after depolarizations; DADs) which has been shown to result in action potentials in single cells and in the intact heart when the aberrant release is adequately synchronized within and among cardiac myocytes.3,4 Factors that lead to DADs include increased heart rate and catecholamine stress, which both induce triggered arrhythmias by increasing SR Ca2+ loading.3 Whereas many molecules are involved in SR Ca2+ overload (DAD) related arrhythmias, abnormal opening …