Multiphoton Imaging of Ca2+ Instability in Acute Myocardial Slices from a RyR2R2474S Murine Model of Catecholaminergic Polymorphic Ventricular Tachycardia.

Giulia Borile,Tania Zaglia,Marco Mongillo,Stephan E Lehnart

doi:10.3390/jcm10132821

Abstract

Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT) is a familial stress-induced arrhythmia syndrome, mostly caused by mutations in Ryanodine receptor 2 (RyR2), the sarcoplasmic reticulum (SR) Ca2+ release channel in cardiomyocytes. Pathogenetic mutations lead to gain of function in the channel, causing arrhythmias by promoting diastolic spontaneous Ca2+ release (SCR) from the SR and delayed afterdepolarizations. While the study of Ca2+ dynamics in single cells from murine CPVT models has increased our understanding of the disease pathogenesis, questions remain on the mechanisms triggering the lethal arrhythmias at tissue level. Here, we combined subcellular analysis of Ca2+ signals in isolated cardiomyocytes and in acute thick ventricular slices of RyR2R2474S knock-in mice, electrically paced at different rates (1–5 Hz), to identify arrhythmogenic Ca2+ dynamics, from the sub- to the multicellular perspective. In both models, RyR2R2474S cardiomyocytes had increased propensity to develop SCR upon adrenergic stimulation, which manifested, in the slices, with Ca2+ alternans and synchronous Ca2+ release events in neighboring cardiomyocytes. Analysis of Ca2+ dynamics in multiple cells in the tissue suggests that SCRs beget SCRs in contiguous cells, overcoming the protective electrotonic myocardial coupling, and potentially generating arrhythmia triggering foci. We suggest that intercellular interactions may underscore arrhythmic propensity in CPVT hearts with ‘leaky’ RyR2.

Highlights

Alterations in intracellular Ca2+ signaling have been associated with a wide variety of cardiovascular pathologies, ranging from myocardial hypertrophy to heart failure and arrhythmias [1,2,3,4]
In accordance with the dominant inheritance of the disease in humans, we investigated Ca2+ dynamics in CMs obtained from mice heterozygous for the RyR2R2474S point mutation (RyR2RS/wt ), previously shown to develop Ca2+ -dependent ventricular arrhythmias and sudden cardiac death (SCD) when exposed to exercise and pharmacologic stress [7]
Mutation negative littermates were used as controls (RyR2wt/wt )

Summary

Introduction

Alterations in intracellular Ca2+ signaling have been associated with a wide variety of cardiovascular pathologies, ranging from myocardial hypertrophy to heart failure and arrhythmias [1,2,3,4]. Patients with RyR2 mutations typically experience sudden arrhythmias during exercise or emotional stresses [5], but may live event-free for decades, even as professional athletes training and competing on a regular basis. This indicates that the development of ventricular arrhythmias initiates when transient mechanisms overcome a protective threshold [10], likely as result of the combination of stress-dependent effects (e.g., activation of sympathetic neurons, SNs) and coincidental factors, not entirely identified

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