Atrial fibrillation (AF) is the most common cardiac arrhythmia, however the mechanism(s) causing AF remain poorly understood and therapy is suboptimal. The ryanodine receptor (RyR2) is the major calcium (Ca²⁺) release channel on the sarcoplasmic reticulum (SR) required for excitation-contraction coupling in cardiac muscle.

In the present study, we sought to determine whether intracellular diastolic SR Ca²⁺ leak via RyR2 plays a role in triggering AF and whether inhibiting this leak can prevent AF.

We generated 3 knock-in mice with mutations introduced into RyR2 that result in leaky channels and cause exercise induced polymorphic ventricular tachycardia in humans [catecholaminergic polymorphic ventricular tachycardia (CPVT)]. We examined AF susceptibility in these three CPVT mouse models harboring RyR2 mutations to explore the role of diastolic SR Ca²⁺ leak in AF. AF was stimulated with an intra-esophageal burst pacing protocol in the 3 CPVT mouse models (RyR2-R2474S^+/−, 70%; RyR2-N2386I^+/−, 60%; RyR2-L433P^+/−, 35.71%) but not in wild-type (WT) mice (P<0.05). Consistent with these in vivo results, there was a significant diastolic SR Ca²⁺ leak in atrial myocytes isolated from the CPVT mouse models. Calstabin2 (FKBP12.6) is an RyR2 subunit that stabilizes the closed state of RyR2 and prevents a Ca²⁺ leak through the channel. Atrial RyR2 from RyR2-R2474S^+/− mice were oxidized, and the RyR2 macromolecular complex was depleted of calstabin2. The Rycal drug S107 stabilizes the closed state of RyR2 by inhibiting the oxidation/phosphorylation induced dissociation of calstabin2 from the channel. S107 reduced the diastolic SR Ca²⁺ leak in atrial myocytes and decreased burst pacing–induced AF in vivo. S107 did not reduce the increased prevalence of burst pacing–induced AF in calstabin2-deficient mice, confirming that calstabin2 is required for the mechanism of action of the drug.

The present study demonstrates that RyR2-mediated diastolic SR Ca²⁺ leak in atrial myocytes is associated with AF in CPVT mice. Moreover, the Rycal S107 inhibited diastolic SR Ca²⁺ leak through RyR2 and pacing-induced AF associated with CPVT mutations.