Ca2+-related signaling and protein phosphorylation abnormalities play central roles in a new experimental model of electrical storm

Abstract

Background-: Electrical storm (ES), characterized by recurrent ventricular tachycardia/fibrillation, typically occurs in implantable cardioverter- defibrillator patients and adversely affects prognosis. However, the underlying molecular basis is poorly understood. In the present study, we report a new experimental model featuring repetitive episodes of implantable cardioverter-defibrillator firing for recurrent ventricular fibrillation (VF), in which we assessed involvement of Ca-related protein alterations in ES. Methods and results-: We studied 37 rabbits with complete atrioventricular block for 80 days, all with implantable cardioverter-defibrillator implantation. All rabbits showed long-QT and VF episodes. Fifty-three percent of rabbits developed ES (3 VF episodes per 24-hour period; 103±23 VF episodes per rabbit). Expression/phosphorylation of Ca-handling proteins was assessed in left ventricular tissues from rabbits with the following: ES; VF episodes but not ES (non-ES); and controls. Left ventricular end-diastolic diameter increased comparably in ES and non-ES rabbits, but contractile dysfunction was significantly greater in ES than in non-ES rabbits. ES rabbits showed striking hyperphosphorylation of Ca/calmodulin-dependent protein kinase II, prominent phospholamban dephosphorylation, and increased protein phosphatase 1 and 2A expression versus control and non-ES rabbits. Ryanodine receptors were similarly hyperphosphorylated at Ser2815 in ES and non-ES rabbits, but ryanodine receptor Ser2809 and L-type Ca channel α-subunit hyperphosphorylation were significantly greater in ES versus non-ES rabbits. To examine direct effects of repeated VF/defibrillation, VF was induced 10 times in control rabbits. Repeated VF tissues showed autophosphorylated Ca/calmodulin-dependent protein kinase II upregulation and phospholamban dephosphorylation like those of ES rabbit hearts. Continuous infusion of a calmodulin antagonist (W-7) to ES rabbits reduced Ca/calmodulin-dependent protein kinase II hyperphosphorylation, suppressed ventricular tachycardia/fibrillation, and rescued left ventricular dysfunction. Conclusions-: ES causes Ca/calmodulin-dependent protein kinase II activation and phospholamban dephosphorylation, which can explain the vicious cycle of arrhythmia promotion and mechanical dysfunction that characterizes ES. © 2011 American Heart Association, Inc.