Effect Of Postconditioning On Isolated Rat Myocardial And Mitochondrial Function

Objective:To investigate the protective effect of postconditioning on isolated rat myocardial and mitochondrial function during ischemia/reperfusion with the Langendorff apparatus,and to study the role of opening the mitochondrial ATP-sensitive potassium channel in myocardial protection.Methods:Langendorff apparatus were used to establish the model of myocardial ischemia reperfusion injury.Sprague-Dawley male rats were randomized into six groups (n=8,each group):continuous reperfusion group(C),control group(CON),diazoxide postconditioning group(DZ),5-hydroxydecanoate plus diazoxide group(5-HD+DZ), ischemic postconditioning(IPO) and 5-HD plus IPO group(5HD+IPO).Hearts isolated from SD rats were mounted on a Langendorff apparatus and started with a 20-min perfusion for equilibration.Group C went on perfusion for another 70 minutes after equilibration group;CON group underwent 40 minutes global ischemia and followed by 30 minutes reperfusion;DZ group started with 20-min perfusion for equilibration,underwent 40 minutes global ischemia,and diazoxide(50μmol/Lof K-H sol) was infused for 5 min,and then reperfusion for 25 min;5-HD+DZ group was perfused with 5-HD(100μmol/Lof K-Hsol) and then diazoxide was administered as that inDZ group;IPO started with 20-min perfusion for equilibration,fellowed by 40 minutes global ischemia and then reperfusion for 10 secnds,and arrested for 10 secnds.The above procedures were repeated 6 times and after that ischemia and then reperfusion 28 minute;In 5-HD+IPO group,5-HD(100μmol/Lof K-Hsol) was perfused before Ischemic postconditioning and the same procedure carded out in IPO group.The following parameters were measured:the recovery of myocardial function,myocardial creatase, reactive oxygen species,membrane potential,respiratory function and cardiolipin of mitochondria were determined with HPLC.Results:1.The myocardial function,mitochondrial membrane potential,respiratory function (Succinate substrate)and cardiolipin of six groups at the end of reperfusion were injured obviously,if compared with those at the end of equilibrium.Myocardial creatase and rate of generation of reactive oxygen species(Succinate substrate) were increased;at the end of reperfusion,the mitochondrial function and cardilipin of DZ group were better than that in IPO group,no difference was found between 5-HD+DZ group and CON group; mitochondrial function and cardilipin of 5-HD+IPO group were better than that in CON group,but still inferior to that of IPO group.2.At the end of reperfusion,while used malate and Glutamate as substrate,the mitochondrial respiratory function of 5-HD+IPO group surpass CON group and increase rate of generation ROS less in CON group;At the end of reperfusion,no matter used vitaminC plus TMPT or malate plus Glutamate substrate,the mitochondrial respiratory function of 5-HD+IPO group outstrip CON group;there are no difference in respiratory function or rate of generation ROS were found in 5-HD+DZ group and DZ group.Conclusions:1.Diazoxide/ischemic postconditioning could attenuate the reperfusion injury,improve myocardial function,decrease myocardial creatase,decrease the generation of ROS, maintain MMP,preserve mitochondrial respiratory function and cardiolipin,all of which will certainly provided better effect of cardioprotection.2.As a mitochondrial ATP sensitive potassium channel antagonist,5-hydroxydecanoate could block the diazoxide postconditioning cardioprotection effectes after endreperfusion, and attenuate the myocardial protect effectes of postconditioning.3.Ischemic postconditioning may play an important role in preserving mitochondrial NADH and succinate respiratory chain,but only diazoxide preserving mitochondrial succinate respiratory chain.4.Diazoxide/ ischemic postconditioning may activate mitochondrial ATP sensitive channels resulted in decrease in generation of ROS,better maintaining of MMP and preserving mitochondrial function and myocardial mitochondrial cardiolipin may be one of the major mechanisms against myocardial ischemia/reperfusion injury,may act as the effectors of cardioprotection.