Effects Of Volume-activated Cl～- Chloride Channel On Myocardial Ischemia/reperfusion Injury

Background and ObjectiveAcute myocardial infarction is the capital causes of death in coronary artery disease (CAD) patients. Recover myocardial blood perfusion is considered as a major therapeutic target of anti-ischemia treatments, But reperfusion induced additional injury, named as reper-fusion injury. Ischemia/reperfusion injury of the myocardium is a complex phenomenon, including myocardial cell necrosis and apoptosis, arrhythmia, and myocardial stunning. Among these pathological processes, A new vision of lethal reperfusion injury as a solidly documented and potentially relevant phenomenon is now widely shared. According to this view, the largest fraction of cardiomyocyte death associated with reperfusion (a) occurs during the initial minutes of re-flow, (b) involves rupture of the cell membrane, (c) is due tomechanisms originating in the cardiomyocytes rather than vascular or blood-born cells, and (d) can be prevented by interventions applied at the time of reperfusion.In recent years, the effects of anion channel, especially the volume activated Cl^- channel (I_Cl,Vol) on myocardial ischemia-reperfusion injury have been highly regarded. I_Cl,Vol) are extensively expressed in the cardiovascular system and play a most important role in cell volume regulation.Among the various methods to protect myocardial ischemia/ reperfusion, more attention has been paid on cell volume regulation, which involve in cell survival. Myocardial reperfusion-induced necrosis and apoptosis which both accompany with pathological cell volume alter occurred simultaneously and both contributed to cardiac reperfusion injury. However, as a major mediator of cell volume regulation, no report yet has illuminated the role of I_Cl,Vol) in the ischemia/reperfusion induced cardiac myocyte death.Several reports have demonstrated that I_Cl,Vol) is not only a mediator of apoptosis, but also may involve in necrosis. But the role and detail mechanisms of I_Cl,Vol) in reperfusion-induced cardiac myocyte death is still not clear. On the other hand, whether I_Cl,Vol) involves in ischemia/ reperfusion induced arrhythmia also remains unclear.To answer these questions, the aims of the present study were: (1) to determine the roles of I_Cl,Vol) in arrhythmia induced by myocardial ischemia/reperfusion; (2) to investigate the effect of I_Cl,Vol) on cardiac myocyte necrosis induced by ischemia/reperfusion; (3) to investigatethe effect of I_Cl,Vol on cardiac myocyte apoptosis induced by ischemia/ reperfusion; Further study is designed to explore detail mechanism of influence of I_Cl,Vol on ischemia/reperfusion myocardium.Results1. NFA (10μmol/L), NPPB (1 μmol/L) and TAM (10 μmol/L), the blocker of I_Cl,Vol, strongly reduced the arrhythmia index in the period of ischemia(P<0.01 versus control, n=10), but has no significant influence on that during reperfusion.2. In the initial stage of reperfusion, NFA (10μmol/L, NPPB (1 μmol/L) and TAM (10 μmol/L) increased significantly the heart infarct size. However, the blocker of I_Cl,Vol reduced the myocardial infarction during later reperfusion (P<0.05 versus control,n=10).3. In cultured neonatal rat cardiomyocytes, simulated ischemia/ reperfusion induced significant myocyte necrosis and apoptosis. After 3 hours simulated ischemia, lots of necrotic cardiac myocytes were observed. After 4 hours simulated reperfusion, cardiac myocytes apoptosis began to occur (P<0.05 versus control, n=5).4. NFA (50μmol/L), NPPB (10 μmol/L) and TAM (10 μmol/L) markedly increased cardiac myocytes necrosis during ischemia and earlier reperfusion (P<0.05 versus control, n=8)5. NFA (50μmol/L), NPPB (10μmol/L) and TAM (10 μmol/L) significantly inhibited cardiac myocytes apoptosis during later reperfusion (P<0.01 versus control, n=6).6. In addition, in the isolated heart ischemia/reperfusion model, we found that the HEPES used as buffer significantly decreased...