BACKGROUNDStudies suggested that anesthetics administered upon the early reperfusion or "anesthetic postconditioning" could protect post-ischemic hearts against myocardial ischemia reperfusion injury (MIRI). However, the mechanism responsible for such protection was not well-elucidated. We investigated the cardioprotection induced by sevoflurane postconditioning (SpostC) in rat hearts in vitro, and the respective role of phosphatidylinositol-3-kinase (PI3K), extracellular signal-regulated kinase 1 and 2 (ERK 1/2), mitochondrial K(ATP) channels (mitoK(ATP)) and mitochondrial permeability transition pore (mPTP), by selectively inhibiting PI3K, ERK 1/2, mitoK(ATP), with LY294002 (LY), PD98059 (PD), 5-hydroxydecanoate (5-HD) and by directly opening of mPTP with atractyloside (ATR), respectively.

METHODSIsolated rat hearts were randomly assigned to one of the 12 groups (n = 15): Time control (continuous perfusion), ISCH (30 minutes of ischemia followed by 60 minutes of reperfusion alone), SpostC (3% sevoflurane postconditioning was administered during the first 15 minutes of reperfusion after 30 minutes of ischemia), ISCH + LY, ISCH + PD, ISCH + ATR, ISCH + 5-HD and ISCH + dimethyl sulfoxide (DMSO) groups (LY, PD, ATR, 5-HD and DMSO (the vehicle) was administered respectively during the first 15 minutes of reperfusion following test ischemia), SpostC + LY, SpostC + PD, SpostC + ATR and SpostC + 5-HD groups (LY, PD, ATR and 5-HD was coadministered with 3% sevoflurane, respectively). Hemodynamics was compared within and between groups. Infarction size was determined at the end of experiments using triphenyltetrazolium chloride (TTC) staining. Lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB) and cardiac troponin I (cTnI) released from necrotic myocardium, were compared among TC, ISCH and SpostC groups. To investigate the relationships between RISK and mPTP implicated in SpostC, NAD(+) content in myocardium, a marker of mPTP opening, was compared among some experimental groups (TC, ISCH, ISCH + LY, ISCH + PD, ISCH + DMSO, SpostC, SpostC + LY, SpostC + PD). To further investigate whether the anti-apoptotic mechanism is implicated in SpostC-induced cardioprotection and its association with mitochondria, TUNEL staining was performed in some experimental groups (TC, ISCH, ISCH + 5-HD, ISCH + ATR, ISCH + DMSO, SpostC, SpostC + 5-HD, SpostC + ATR).

RESULTSWhen compared with unprotected hearts subjected to 30 minutes of ischemia, exposure to 3% sevoflurane for 15 minutes during early reperfusion significantly improved functional recovery, decreased myocardial infarct size, decreased LDH, CK-MB and cTnI release, and decreased cardiomyocyte apoptosis (P < 0.05). However, such cardioprotective effects of hemodynamic recovery and infarct size reduction by sevoflurane was completely abolished by any one of LY294002, PD98059, atractyloside and 5-hydroxydecanoate (P < 0.05). Additionally, either LY294002 or PD98059 could reverse the inhibitory effect of SpostC over mPTP opening upon reperfusion (P < 0.05). Both atractyloside and 5-hydroxydecanoate could abrogate the anti-apoptotic effects of SpostC (P < 0.05).

CONCLUSIONThese findings demonstrate that PI3K, ERK 1/2, mitoK(ATP) and mPTP are key players in sevoflurane postconditioning induced cardioprotective mechanisms in isolated rat hearts subjected to MIRI.