Involvement Of κ-Opioid Receptor In Ischemic Preconditioning And The Underlying Mechanism

The primary purpose of the study was to determine whether K-opioid receptor (OR) mediated cardioprotection of ischemic preconditioning (IPC) and the underlying mechanism.Firstly, two series of experiments were performed in the isolated perfused rat heart, hi the first series of experiments, the effects of IPC on infarct induced by ischemia were determined with blockade of either K- or 5-OR. Regional ischemia of 30 min induced infarct, which was ameliorated by IPC with two cycles of 5 min regional ischemia followed by 5 min reperfusion each. The ameliorating effect of IPC on infarct was attenuated by either 5 x 10"6 mol/L BNI, a selective K-OR antagonist, or 5 x 10"* mol/L. NTD, a selective 5-OR antagonist. In the second series of experiments, U50,488H, a selective K-OR agonist, or DADLE, a selective 5-OR agonist, was also administered for two cycles of 5 min each. The treatment also reduced dose-dependently the infarct size induced by ischemia, which mimicked the effects of IPC. The effect of 10-5 mol/L U50,488H on infarct was significantly attenuated by blockade of PKC with specific PKC inhibitors, 5 x 10-6 mol/L. chelerythrine or 8 x 10~7 mol/L calphostin C, as well as by blockade of KATP channel with blockers of the channel, 10-5 mol/L glibenclamide or 10-4 mol/L 5-hydroxydecanoate. IPC also reduced arrhythmia induced by ischemia. BNI, but not NTD, attenuated, while U50,488H, but not DADLE, mimicked theantiarrhythmic action of IPC. In conclusion, the present study has provided first evidence that K-OR mediates the ameliorating effects of IPC on infarct and arrhythmia induced by ischemia, while 6-OR on infarct only. Both PKC and KATP channel in turn mediate cardioprotection of activation of K-OR in terms of infarct.Secondly, we identified the PKC isoforms and KATP channels in delayed cardioprotection of MIP and K-OR stimulation. Both MIP and U50,488H pretreatment (10~5 mol/L) increased translocation of PKC epsilon (e) from cytosolic to membrane fractions, which was accompanied by reductions in release of lactate dehydrogenase (LDH) and cell death upon delayed lethal simulated ischemia and reperfusion in rat cardiomyocytes. 10"7 mol/L Phorbol 12-myristate 13-acetate (PMA), a PKC activator, mimicked, while 5x10"* mol/L chelerythrine, a PKC inhibitor, and 10'7 mol/L eVl-2, the PKC-s selective inhibitor attenuated the effects of both treatments. In addition, 10"4 mol/L 5-hydroxydecanoate (5-HD), a mitochondrion-selective KATP channel inhibitor, but not 3x 10'5 mol/L HMR1098, a sarcolemma-selective KATP channel inhibitor, abolished the cardioprotection of MIP, pretreatment with U50,488H or PMA. The results indicate that both PKC-s and mitochondria! KATP channel mediate delayed cardioprotection of K-opioid stimulation and MIPIn conclusion, the present study has provided first evidence that K-OR mediates the ameliorating effects of IP on infarct and arrhythmia induced by ischemia, while 6-OR on infarct only. Both PKC-s and mitochondrial KATP channel mediate delayed cardioprotection of K-opioid stimulation and MIP.