Ryanodine Receptor Mutations Associated With Stress-Induced Ventricular Tachycardia Mediate Increased Calcium Release in Stimulated Cardiomyocytes

Abstract

Ca 2+ release from the sarcoplasmic reticulum mediated by the cardiac ryanodine receptor (RyR2) is a fundamental event in cardiac muscle contraction. RyR2 mutations suggested to cause defective Ca 2+ channel function have recently been identified in catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular dysplasia (ARVD) affected individuals. We report expression of three CPVT-linked human RyR2 (hRyR2) mutations (S 2246 L, N 4104 K, and R 4497 C) in HL-1 cardiomyocytes displaying correct targeting to the endoplasmic reticulum. N 4104 K also localized to the Golgi apparatus. Phenotypic characteristics including intracellular Ca 2+ handling, proliferation, viability, RyR2:FKBP12.6 interaction, and beat rate in resting HL-1 cells expressing mutant hRyR2 were indistinguishable from wild-type (WT) hRyR2. However, Ca 2+ release was augmented in cells expressing mutant hRyR2 after RyR activation (caffeine and 4-chloro-m-cresol) or β-adrenergic stimulation (isoproterenol). RyR2:FKBP12.6 interaction remained intact after caffeine or 4-CMC activation, but was dramatically disrupted by isoproterenol or forskolin, an activator of adenylate cyclase. Isoproterenol and forskolin elevated cyclic-AMP to similar magnitudes in all cells and were associated with equivalent hyperphosphorylation of mutant and WT hRyR2. CPVT-linked mutations in hRyR2 did not alter resting cardiomyocyte phenotype but mediated augmented Ca 2+ release on RyR-agonist or β-AR stimulation. Furthermore, equivalent interaction between mutant and WT hRyR2 and FKBP12.6 was demonstrated.