Protective Effects And Mechanisms Of Ranolazine Postconditioning Against Ischemia-Reperfusion Injury In Hearts

PARTⅠPROTECTIVE EFFECTS OF RANOLAZINE POSTCONDITIONING AGAINST ISCHEMIA-REPERFUSION INJURY IN ISOLATED RAT HEARTSObjective To investigate the protective effects of ranolazine postconditioning (various concentrations) against ischemia-reperfusion injury in isolated rat hearts and compare the effects of ranolazine postconditioning with ranolazine preconditioning.Methods 48 SD rat hearts were randomly assigned to receive K-H buffer (C group,n=8),ischema and reperfusion (I/R group,n=8), 20μmol/L ranolazine preconditioning (RPreC group,n=8),or 5, 10 or 20μmol/L ranolazine postconditioning (RPostC1,RPostC2 and RPostC3 group respectively, n=8 respectively). All hearts were perfused in the langendorff mode. Cardiac function variables (Heart Rate,Left ventricular developed pressure, and±dp/dtmax)and coronary flow were measured all the points during this protocol. The activities of CK, LDH and CTn-I in coronary effluent were measured at baseline (the end of equilibration) and the end of reperfusion.Results Ranolazine didn't significantly decrease the preischaemic values of cardiac function and coronary flow (P>0.05). Cardiac function and coronary flow was improved (P<0.05 vs. I/R group) in all ranolazine groups , especially in RPostC3 and RPreC group compared with RPostC1 or RPostC2 group (P<0.05) at the end of reperfusion. The differences between RPostC3 and RPreC groups were not significant. The changes of CK, LDH and CTn-I activities in coronary effluent were consistent with cardiac function variables and coronary flow.Conclusion Ranolazine has no effect on cardiac function and coronary flow in normal rat hearts at concentrations≤20μmol/L. Ranolazine prevents isolated rat hearts subjected to ischemia and reperfusion in a concentration dependent manner.The cardioprotective effects of 20μmol/L ranolazine are comparable to ranolazine preconditioning.PARTⅡSTUDY OF MECHANISMS OF RANOLAZINE POSTCONDITIONING AGAINST ISCHEMIA-REPERFUSION INJURY IN ISOLATED RAT HEARTSObjective To study the possible mechanisms of ranolazine postconditioning against ischemia-reperfusion injury in isolated rat hearts.Methods 48 SD rat hearts were randomly assigned to receive ischema and reperfusion (I/R group,n=6), 20μmol/L ranolazine postconditioning (RPostC group,n=6), ranolazine and the specific PI3K inhibitor wortmannin (RW group, n=6), ranolazine and the specific Erk1/2 inhibitor PD 098059 (RP group,n=6),ranolazine and the specific mPTP opener atractyloside (RA group,n=6), wortmannin (W group,n=6), PD98059 (P group, n=6), or atractyloside (A group, n=6). All hearts were perfused in the langendorff mode. The activities of CK, LDH and CTn-I in coronary effluent, AKT phosphorylation,ERK1/2 phosphorylation in left ventricular tissue samples and opening of mPTP were measured 15min after reperfusion. Cardiac apex tissue samples of five hearts randomly obteined from I/R, RPostC,RW,RP and RA groups respectively after 60min of reperfusion and ultrastructural organizations were observed by a transmission electron microscope.Results There were no differences (P>0.05) in the activities of CK, LDH and CTn-I in coronary effluent 15min after reperfusion among W, P, A and RA groups. The activities of CK, LDH and CTn-I in coronary effluent in RW and RP group were decreased compared with RA or I/R group (P<0.05) and increased compared with RPost group (P<0.05). The changes of opening of mPTP,transmission electron microscopy images,AKT phosphorylation and ERK1/2 phosphorylation (except RA group) were consistent with biochemical results. AKT phosphorylation and ERK1/2 phosphorylation in myocardium were no differences (P>0.05) between RA and RPostC groups.Conclusion Ranolazine mimics the cardioprotective effects of ischemic postconditioning by activation of PI3k-AKT and ERK1/2 signaling pathways and inhibition of the opening of mPTP against ischemia-reperfusion injury.Possibly ranolazine postconditioning has other mechanisms in which RISK (PI3K- AKT and ERK1/2) signaling pathway has not been implicated.mPTP is the downstream mediator of RISK signaling pathway. There may be crossroads between PI3K-AKT and ERK1/2 signaling pathways.PARTⅢSTUDY OF THE RELATIONSHIP BETWEEN THE INFLUENCES OF RANOLAZINE POSTCONDITIONING ON MYOCARDIAL APOPTOSIS AND THE OPENING OF MPTP IN ISOLATED RAT HEARTS SUBJECTED TO ISCHEMIA AND REPERFUSIONObjective To investigate whether ranolazine postconditioning can attenuates myocardial apoptosis via inhibition of the opening of mPTP in isolated rat hearts subjected to ischemia and reperfusion.Methods 18 SD rat hearts were randomly assigned to receive ischema and reperfusion (I/R group, n=5), 20μmol/L ranolazine postconditioning (RPostC group, n=4), ranolazine and the specific mPTP opener atractyloside (RA group, n=5), or atractyloside (A group,n=4).All hearts were perfused in the langendorff mode.Myocardial apoptosis (TUNEL-positive cells), apoptotic index (AI) and the opening of mPTP were measured at the end of reperfusion.Results Ranolazine postconditioning significantly reduced myocardial apoptosis compared with I/R group (P<0.05). There were no significant differences in myocardial apoptosis among I/R group, RA group and A groups (P>0.05). The changes of AI and opening of mPTP were consistent with myocardial apoptosis.Conclusion Ranolazine postconditioning attenuates myocardial apoptosis via inhibition of the opening of mPTP in isolated rat hearts subjected to ischemia and reperfusion...