AIMS: Mutations in the cardiac ryanodine receptor Ca(2+) release channel, RyR2, 
underlie catecholaminergic polymorphic ventricular tachycardia (CPVT), an 
inherited life-threatening arrhythmia. CPVT is triggered by spontaneous 
RyR2-mediated sarcoplasmic reticulum (SR) Ca(2+) release in response to SR 
Ca(2+) overload during beta-adrenergic stimulation. However, whether elevated SR 
Ca(2+) content--in the absence of protein kinase A activation--affects RyR2 
function and arrhythmogenesis in CPVT remains elusive.
METHODS AND RESULTS: Isolated murine ventricular myocytes harbouring a human 
RyR2 mutation (RyR2(R4496C+/-)) associated with CPVT were investigated in the 
absence and presence of 1 micromol/L JTV-519 (RyR2 stabilizer) followed by 100 
micromol/L ouabain intervention to increase cytosolic [Na(+)] and SR Ca(2+) 
load. Changes in membrane potential and intracellular [Ca(2+)] were monitored 
with whole-cell patch-clamping and confocal Ca(2+) imaging, respectively. At 
baseline, action potentials (APs), Ca(2+) transients, fractional SR Ca(2+) 
release, and SR Ca(2+) load were comparable in wild-type (WT) and 
RyR2(R4496C+/-) myocytes. Ouabain evoked significant increases in diastolic 
[Ca(2+)], peak systolic [Ca(2+)], fractional SR Ca(2+) release, and SR Ca(2+) 
content that were quantitatively similar in WT and RyR2(R4496C+/-) myocytes. 
Ouabain also induced arrhythmogenic events, i.e. spontaneous Ca(2+) waves, 
delayed afterdepolarizations and spontaneous APs, in both groups. However, the 
ouabain-induced increase in the frequency of arrhythmogenic events was 
dramatically larger in RyR2(R4496C+/-) when compared with WT myocytes. JTV-519 
greatly reduced the frequency of ouabain-induced arrhythmogenic events.
CONCLUSION: The elevation of SR Ca(2+) load--in the absence of beta-adrenergic 
stimulation--is sufficient to increase the propensity for triggered arrhythmias 
in RyR2(R4496C+/-) cardiomyocytes. Stabilization of RyR2 by JTV-519 effectively 
reduces these triggered arrhythmias.