Atp-induced cardioprotection against myocardial ischemia/reperfusion injury is mediated through risk pathway

Abstract

Objective: Adenosine-5'-triphosphate (ATP) has been reported to protect the heart from myocardial ischemia/reperfusion injury when administered at the onset of reperfusion and is as effective as mechanical postconditioning. However, whether the protective effect of postconditioning with ATP is mediated through the same signaling pathways as those of ischemic postconditioning is still unclear. We examined the postinfarct acute effect of ATP on myocardial infarct size and its precise molecular mechanism. Methods: Forty-eight New Zealand white male rabbits were exposed to 40 min of ischemia followed by 180 min of reperfusion. Rabbits were intravenously injected 3mg/kg of ATP (ATP group) or saline (control group) immediately after reperfusion within 30min. The wortmannin+ATP, PD-98059+ATP, and 5-hydroxydecanoic acid sodium salt (5-HD)+ATP groups were respectively injected with wortmannin [a phosphatidyl-inositol 3-kinase (PI3-kinase) inhibitor, 0.6 mg/kg], PD-98059 [an extracellular signal regulated protein kinase (ERK) inhibitor, 0.3 mg/kg], and 5-HD [a mitochondrial ATP-dependent K+ (KATP) channel blocker, 5 mg/kg] 5 min before ATP administration. Myocardial infarct size was calculated as a percentage of the risk area of the left ventricle. Myocardial apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) methods. Western blot analysis was performed to examine the signals such as protein kinase B (Akt) and extracellular signal-regulated protein kinase (ERK) in the ischemic myocardium after 180min of reperfusion. Results: The infarct size was significantly smaller in the ATP group (12.8±1.9%) than in the control group (29.1±2.9%). The infarct size-reducing effect of ATP was completely blocked by wortmannin (26.5±2.7%), PD-98059 (27.9±3.2%), and 5-HD (26.1±4.0%). Compared with control group, ATP group significantly reduced cardiomyocytes apoptosis (apoptotic index: 27.0±5.8% vs 10.3±6.0%, P<0.05), while wortmannin+ATP group (20.7±4.3%), PD-98059+ATP (25.5±4.9%) group and 5-HD+ATP (21.2±3.6%) not. Western blot analysis showed higher myocardial expression of phospho-Akt, phospho-ERK at 180 min after reperfusion in the ATP group than in the control group. Conclusion: Cardioprotection by postischemic ATP administration is mediated through activation of the reperfusion injury salvage kinase pathway and opening of the mitochondrial ATP-dependent K+ channels.