SR Ca 2+ -leak and disordered excitation-contraction coupling as the basis for arrhythmogenic and negative inotropic effects of acute ethanol exposure.

AIMS: Ethanol has acute negative inotropic and arrhythmogenic effects. The underlying mechanisms, however, are largely unknown. Sarcoplasmic reticulum Ca2+ -leak is an important mechanism for reduced contractility and arrhythmias. Ca2+ -leak can be induced by oxidative stress and Ca2+ /Calmodulin-dependent protein kinase II (CaMKII). Therefore, we investigated the influence of acute ethanol exposure on excitation-contraction coupling in atrial and ventricular cardiomyocytes.

METHODS AND RESULTS: Isolated human atrial and murine atrial or ventricular cardiomyocytes were preincubated for 30 min and then superfused with control solution or solution containing ethanol. Ethanol had acute negative inotropic and positive lusitropic effects in human atrial muscle strips and murine ventricular cardiomyocytes. Accordingly, Ca2+ -imaging indicated lower Ca2+ -transient amplitudes and increased SERCA2a activity, while myofilament Ca2+ -sensitivity was reduced. SR Ca2+ -leak was assessed by measuring Ca2+ -sparks. Ethanol induced severe SR Ca2+ -leak in human atrial cardiomyocytes (calculated leak: 4.60 ± 0.45 mF/F0 vs 1.86 ± 0.26 in control, n ≥ 80). This effect was dose-dependent, while spontaneous arrhythmogenic Ca2+ -waves increased ~5-fold, as investigated in murine cardiomyocytes. Delayed afterdepolarizations, which can result from increased SR Ca2+ -leak, were significantly increased by ethanol. Measurements using the reactive oxygen species (ROS) sensor CM-H2 DCFDA showed increased ROS-stress in ethanol treated cells. ROS-scavenging with N-acetylcysteine prevented negative inotropic and positive lusitropic effects in human muscle strips. Ethanol-induced Ca2+ -leak was abolished in mice with knockout of NOX2 (the main source for ROS in cardiomyocytes). Importantly, mice with oxidation-resistant CaMKII (Met281/282Val mutation) were protected from ethanol-induced Ca2+ -leak.

CONCLUSION: We show for the first time that ethanol acutely induces strong SR Ca2+ -leak, also altering excitation-contraction coupling. Acute negative inotropic effects of ethanol can be explained by reduced systolic Ca2+ -release. Mechanistically, ROS-production via NOX2 and oxidative activation of CaMKII appear to play central roles. This provides a mechanism for the arrhythmogenic and negative inotropic effects of ethanol and suggests a druggable target (CaMKII).