Protective Effects Of Ischemia Postconditioning On Myocardial Mitochondrial In Isolated Rats

Objective:To investigate the effects of ischemia postconditioning(IPO)on myocardial ischemia reperfusion injury(MIRI) to isolated rat heart.Focusing on the effects of IPO on myocardial mitochondrial,it includes mitochondrial Ca²⁺ uptake,regulation of mitochondrial permeability transition pore(mPTP),the activities of the respiratory chain complexes in mitochondrial,lactate dehydrogenase(LDH) activity and the myocardial infarct size.Methods:Sixteen Wistar rats were randomly divided into two groups:the control group (ischemia reperfusion group) and the postconditioning group(n=8).The isolated heart was perfused by the Langendorff method.Control group,isolated rat hearts were perfused with Krebs-Henseleit(K-H) perfusion buffer and maintained for 10 min of heart working,ischemia for 30 min and reperfused for 3 h.;to the postconditioning group,it consisted of 3 episodes of 30 seconds of coronary occlusion and 30 seconds of reperfusion after the 30 min global myocardial ischemia and then 3 h reperfusion. The LDH activity was determined by ultraviolet spectrophotometry and the infarct size was assessed by triphenyltetrazolium staining.Myocardial mitochondria taken from myocardium were prepared with differential centrifugation.The opening of mPTP,the Ca²⁺ uptake of myocardial mitochondria.and the activities of the respiratory chain complexes in mitochondrial were observed by spectrophotometry. The protein concentration was determined by Folin-Phenol method.Results:1 Effects of IPO on LDH activity and infarct size of rat heartsThe LDH activity in IPO group was lower than that in control group(P＜0.01);The myocardial infarct size in IPO group was less than that in control group(P＜0.01 ).2 Effects of IPO on the regulation of mPTP in myocardial ischemia reperfusion injury ratsThe releasing rate and maximum of cytochrome C(Cyt C) of the control group are significantly higher than that of postconditioning group(P＜0.01)3 Effects of IPO on the activities of the respiratory chain complexes in mitochondrialThe activities of the respiratory chain complexes(complexâ… ,â…¡,â…£) in mitochondrial in IPO group were higher than in control group(P＜0.01).4 Effects of IPO on myocardial mitochondria Ca²⁺ uptakeThe maxium of Ca²⁺ uptake of myocardial mitochondria in IPO group was lower than in control group(P＜0.01 ).Conclusions:1 IPO can reduce the myocardial infarct size and the LDH release of myocardial cells.Consequently,IPO can protect ischemia-reperfused myocardium.2 IPO can inhibits opening of the mPTP,decreases the releasing of Cyt C and reduce apoptosis of myocardial cells.Therefore it provides a powerful antiischemic protection.3 IPO can enhance the activities of the respiratory chain complexes in mitochondrial.So IPOcan protect the mitochondria to produce ATP and provide energy for cells.4 IPO reduced Ca²⁺ uptake,indicating that IPO can reduce the mitochondria Ca²⁺ overload and avoid the high-permeability state of mPTP,swelling of mitochondria decreasing of ATP which are all due to mitochondrial calcium overload.Consequently,IPO can protect ischemia-reperfused myocardium.The results of this study indicate that IPO can protect ischemia-reperfused myocardium and the mitochondria takes an important part.The findings might provide new clue for further researches on the protective mechanisms of IPO on myocardial ischemia reperfusion injury.