β-Adrenergic receptor (β-AR) activation can provoke cardiac arrhythmias mediated by cAMP-dependent alterations of Ca²⁺ signaling. However, cAMP can activate both protein kinase A and an exchange protein directly activated by cAMP (Epac), but their functional interaction is unclear. In heart, selective Epac activation can induce potentially arrhythmogenic sarcoplasmic reticulum (SR) Ca²⁺ release that involves Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) effects on the ryanodine receptor (RyR).

We tested whether physiological β-AR activation causes Epac-mediated SR Ca²⁺ leak and arrhythmias and whether it requires Epac1 versus Epac2, β₁-AR versus β₂-AR, and CaMKIIδ-dependent phosphorylation of RyR2-S2814. We used knockout (KO) mice for Epac1, Epac2, or both. All KOs exhibited unaltered basal cardiac function, Ca²⁺ handling, and hypertrophy in response to pressure overload. However, SR Ca²⁺ leak induced by the specific Epac activator 8-CPT in wild-type mice was abolished in Epac2-KO and double-KO mice but was unaltered in Epac1-KO mice. β-AR–induced arrhythmias were also less inducible in Epac2-KO versus wild-type mice. β-AR activation with protein kinase A inhibition mimicked 8-CPT effects on SR Ca²⁺ leak and was prevented by blockade of β₁-AR but not β₂-AR. CaMKII inhibition (KN93) and genetic ablation of either CaMKIIδ or CaMKII phosphorylation on RyR2-S2814 prevented 8-CPT–induced SR Ca²⁺ leak.

β₁-AR activates Epac2 to induce SR Ca²⁺ leak via CaMKIIδ-dependent phosphorylation of RyR2-S2814. This pathway contributes to β-AR–induced arrhythmias and reduced cardiac function.