Résumé
Atrial Fibrillation (AF) is a high prevalence sustained cardiac arrythmia whose pathogenesis is characterized by electrophysiological dysregulations such as Action Potential Duration (APD) modulation. Recently, the downstream effectors of cAMP, EPAC have been identified as putative AF promotor by APD lengthening in mice. However, the ability of EPAC to remodel the human atrial cardiomyocyte's electrophysiology remains to be determined.
To assess the regulatory role of EPAC and it signaling in atrial myocytes electrophysiology.
Right auricular appendages were collected from patients in Sinus Rhythm (SR) or AF undergoing a cardiopulmonary bypass surgery. EPAC proteins levels were measured by Western Blot (WB). AP and K+ currents (IK) were recorded using the patch clamp technique in enzymatically isolated cardiomyocytes. 8-CPT-AM (10μM), AM-001 (20μM) or ESI-05 (25μM) were acutely perfused to activate EPAC proteins and selectively inhibit EPAC1 and EPAC2, respectively.
In SR cardiomyocytes, 8-CPT-AM induced EPAC activation significantly increased APD by inhibiting the repolarizing IK. Pre-treatments of cells with a selective EPAC1 or EPAC2 blocker revealed that both EPAC isoforms participate to this effect. Selective recordings of the peak transient outward and the two sustained K+ components (ultra-rapid and delayed rectifier mediated, respectively) showed that all of them were downregulated by EPAC activation. Mechanistically, inhibition of Calmodulin Kinase II prevented EPAC-dependent modulation of the peak component of IK, but without affecting the effect on the sustained component. On the contrary, both inhibition of NO-synthases and Protein Kinase G failed to reduce the effect of EPAC on the peak component but prevented the alteration of the sustained component of IK. In cardiomyocytes from SR patients, perfusion of the EPAC1 inhibitor AM-001 after 8-CPT-AM treatment failed to reverse the EPAC-induced alteration of IK. However, the effect of 8-CPT-AM on IK was significantly corrected by AM-001 in cells isolated from AF patients. Finally, WB analysis highlighted that EPAC1, but not EPAC2, protein levels were increased in atria of AF patients compared to SR patients.
Our results show that EPAC signaling increases APD by inhibition of K+ currents in human atrial cardiomyocytes. Further, they suggest that EPAC1 signaling is dysregulated and promote arrhythmogenic activity in AF context.