Multiphoton Imaging of Ca(2+) Instability in Acute Myocardial Slices from a RyR2(R2474S) Murine Model of Catecholaminergic Polymorphic Ventricular Tachycardia

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) Ca(2+) release channel in cardiomyocytes. Pathogenetic mutations lead to gain of function in the channel, causing arrhythmias by promoting diastolic spontaneous Ca(2+) release (SCR) from the SR and delayed afterdepolarizations. While the study of Ca(2+) 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 Ca(2+) signals in isolated cardiomyocytes and in acute thick ventricular slices of RyR2(R2474S) knock-in mice, electrically paced at different rates (1–5 Hz), to identify arrhythmogenic Ca(2+) dynamics, from the sub- to the multicellular perspective. In both models, RyR2(R2474S) cardiomyocytes had increased propensity to develop SCR upon adrenergic stimulation, which manifested, in the slices, with Ca(2+) alternans and synchronous Ca(2+) release events in neighboring cardiomyocytes. Analysis of Ca(2+) 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.