Mice with the R176Q cardiac ryanodine receptor mutation exhibit catecholamine-induced ventricular tachycardia and cardiomyopathy

Mutations in the cardiac ryanodine receptor 2 (RyR2) have been associated with catecholaminergic polymorphic ventricular tachycardia and a form of arrhythmogenic right ventricular dysplasia. To study the relationship between RyR2 function and these phenotypes, we developed knockin mice with the human disease-associated RyR2 mutation R176Q. Histologic analysis of hearts from RyR2^R176Q/+ mice revealed no evidence of fibrofatty infiltration or structural abnormalities characteristic of arrhythmogenic right ventricular dysplasia, but right ventricular end-diastolic volume was decreased in RyR2 ^R176Q/+ mice compared with controls, indicating subtle functional impairment due to the presence of a single mutant allele. Ventricular tachycardia (VT) was observed after caffeine and epinephrine injection in RyR2^R176Q/+, but not in WT, mice. Intracardiac electrophysiology studies with programmed stimulation also elicited VT in RyR2^R176Q/+ mice. Isoproterenol administration during programmed stimulation increased both the number and duration of VT episodes in RyR2^R176Q/+ mice, but not in controls. Isolated cardiomyocytes from RyR2^R176Q/+ mice exhibited a higher incidence of spontaneous Ca²⁺ oscillations in the absence and presence of isoproterenol compared with controls. Our results suggest that the R176Q mutation in RyR2 predisposes the heart to catecholamine-induced oscillatory calcium-release events that trigger a calcium-dependent ventricular arrhythmia.