Abstract 13450: Synchronization of Proarrhythmic Ca2+ Signaling in Cardiac Muscle Harboring a Calsequestrin 2 Mutation Linked to Catecholaminergic Polymorphic Ventricular Tachycardia
Background. Dysregulated intracellular Ca2+ signaling is implicated in a variety of cardiac arrhythmias including Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT). In disease settings, spontaneous Ca2+ waves (SCWs) can induce proarrhythmic plasma membrane depolarizations. Although recent evidence suggest that weakened control of ryanodine receptor (RyR2) activity by sarcoplasmic reticulum (SR) Ca2+ contributes to SCWs generation, the mechanisms responsible for SCWs synchronization among adjacent myocytes required for ectopic activity remain obscure.
Methods. To study the mechanism(s) of arrhythmogenic SCWs synchronization we performed contraction measurements and confocal Ca2+ imaging in isolated myocytes and intact myocardium preparations from wild type (WT) mice and mice featuring CPVT due to the R33Q mutation in the RyR2 regulatory protein cardiac calsequestrin 2.
Results. Restitution of cytosolic Ca2+ transients assessed by a two-pulse protocol was significantly faster in R33Q myocytes compared to WT cells. Frequency of diastolic SCWs in the presence of β-adrenergic agonist isoproterenol (Iso) was significantly higher in R33Q myocytes and time delay between systolic Ca2+ release and SCW consistently shorter and less variable. Addition of Iso to multicellular cardiac preparations induced regular diastolic contractions (DCs) only in R33Q muscles. DCs narrowly clustered around 3 time points during diastole (390, 650, and 880 ms) and had an amplitude distribution skewed towards high values, similar to the average systolic developed force (∼60% of DCs). Confocal Ca2+ imaging of R33Q muscles showed SCWs rising synchronously in all myocytes and preceding global Ca2+ release associated with extrasystolic action potential and DC. In the presence of Iso unstimulated R33Q muscles displayed occasional random SCWs, while systolic Ca2+ release induced by an electrical stimulus resulted in synchronization of SCWs among myocytes
Conclusion. In intact cardiac muscles under conditions mimicking CPVT, SCWs occur with high synchronicity in neighboring cells, as a consequence of shortened store-dependent Ca2+ signaling refractoriness coupled with temporally aligned SR Ca2+ release, thus accounting for triggered activity.
- © 2012 by American Heart Association, Inc.