Epac2 (Exchange Protein directly Activated by cAMP) has recently emerged as a critical player in heart failure and arrhythmia, also seen in diabetes. Hyperglycemia induces SR Ca²⁺ leak and arrhythmia via CaMKII, a downstream effector of Epac2. However, the role of Epac2 in hyperglycemia-mediated SR Ca²⁺ leak is unknown.

To determine the significance of Epac 2 in hyperglycemia-mediated SR Ca²⁺ leak.

Ca²⁺ signaling was measured by confocal microscopy in quiescent ventricular cardiomyocytes, isolated from C56BL6 and Epac2-KO mice, and loaded with Fluo4-AM (5μM). Epac activity was estimated using an Epac-based FRET biosensor. Cells were treated with 100, 300 and 500mg/dl D-glucose±ESI-05 (Epac2 inhibitor).

High glucose increased Ca²⁺ spark frequency (n/100μm/s: 0.13±0.02 at 100mg/dl vs. 0.45±0.12 at 500mg/dl, P<0.05) and diastolic [Ca²⁺] (F0:35.2±2.7 at 100mg/dl vs. 63.7±7.6 at 300mg/dl, P<0.05) leading to Ca²⁺ waves generation (10.52% at 100mg/dl vs. 36% at 500mg/dl). Both ESI-05 and Epac2 deletion reduced hyperglycemic-mediated effects. Furthermore, the increase of Epac-based FRET biosensor activity in high glucose condition was fully blocked by specific O-GlcNAcylation inhibition by diazo-5-oxonorleucine.

This work suggests that hyperglycemia activates Epac2-mediated SR Ca²⁺ leak and pro-arrhythmic event via O-GlcNAcylation.