Upregulation of MMP-9 and CaMKII prompts cardiac electrophysiological changes that predispose denervated transplanted hearts to arrhythmogenesis after prolonged cold ischemic storage.

BACKGROUND: Although the importance of the potential mechanisms of arrhythmogenesis, including cardiac electrophysiology dysfunction and gap junction electrical uncoupling by Cx43 degradation under pathological conditions, has been widely and thoroughly established, the correlations between these mechanisms and biomarkers of cold ischemic insult have not yet been confirmed. Limited evidence suggests that these biomarkers are significantly associated with cardiac dysrhythmia. Thus, in this study, we analyzed such correlations in denervated transplanted hearts.

METHODS AND RESULTS: Rat hearts were divided into two groups according to a random number table. The hearts in the first group were stored in histidine-tryptophan-ketoglutarate (HTK) solution for 6 h to produce cold ischemic insult (insult group, n = 8), while the hearts in the second group were left untreated (control group, n = 8). Ventricular arrhythmias (VAs) were successively observed in 8/8 hearts stored in HTK solution and 0/8 untreated hearts (P < 0.05). The analysis of the electrophysiological parameters by programmed electrical stimulation (PES) and monophasic action potential (MAP) recording demonstrated that compared with the control hearts, the insult hearts had increased transmural dispersion of repolarization (TDR) and effective refractory periods (ERPs) (P < 0.001), decreased conduction velocities (CVs) and excitation wavelengths (CV × ERP, λ) (P < 0.05), and longer times between peak MAP values and 90% repolarization (MAPD90 ) in the epicardium (P < 0.05). However, no significant difference in endocardial MAPD90 was observed between the two groups of hearts. The investigation of biomarkers and Cx43 proteins by a western blot analysis showed that the matrix metalloproteinase-9 (MMP-9) and Ca2+ /calmodulin-dependent protein kinase II (CaMKII) levels were strongly elevated and that the Cx43 protein levels were markedly reduced in the insult hearts.

CONCLUSION: MMP-9 overexpression mediates gap junction (GJ) electrical uncoupling induced by Cx43 decreases, while CaMKII upregulation induces transmural dispersion of repolarization (TDR) increase, both of which increase the risk of ventricular arrhythmias (VAs) in denervated transplanted hearts after prolonged cold ischemic storage.