Exchange protein directly activated by cAMP (Epac) mediates cardiac repolarization and arrhythmogenesis during chronic heart failure

Most sudden cardiac death in chronic heart failure (CHF) is caused by malignant ventricular arrhythmia (VA). However, the molecular mechanism remains unclear. This study aims to explore the effect of exchange proteins directly activated by cAMP (Epac) on VA in CHF and the potential molecular mechanism. Transaortic constriction was performed to prepare CHF guinea pigs. Epac activation model was obtained with 8-pCPT administration. Programmed electrical stimulation (PES) was performed to detect effective refractory period (ERP) or induce VA. Isolated adult cardiomyocytes were treated with 8-pCPT and/or the Epac inhibitor. Cellular electrophysiology was examined by whole-cell patch clamp. With Epac activation, corrected QT duration (QTc) was lengthened by 12.6%. 8-pCPT increased action potential duration (APD) (APD50: 236.9±18.07ms vs. 328.8±11.27ms, p<0.05; APD90: 264.6±18.22ms vs. 388.6±6.47ms, p<0.05) and decreased IKr current (tail current density: 1.1±0.08pA/pF vs. 0.7±0.03pA/pF, p<0.05). PES induced more malignant arrhythmias in the 8-pCPT group than in the control group (3/4 vs. 0/8, p<0.05). The selective Epac1 inhibitor CE3F4 rescued the drop in IKr after 8-pCPT stimulation (tail current density: 0.5 ± 0.02pA/pF vs. 0.6 ± 0.03pA/pF, p<0.05). In conclusion, Epac1 regulates IKr, APD and ERP in guinea pigs, which could contribute to the proarrhythmic effect of Epac1 in CHF.