Signal transduction of opioid-induced cardioprotection in ischemia-reperfusion

Abstract

Background: Morphine reduces myocardial ischemia-reperfusion injury in vivo and in vitro. The authors tried to determine the role of opioid δ1 receptors, oxygen radicals, and adenosine triphosphate-sensitive potassium (KATP) channels in mediating this effect. Methods: Chick cardiomyocytes were studied in a flowthrough chamber while pH, flow rate, oxygen, and carbon dioxide tension were controlled. Cell viability was quantified by nuclear stain propidium iodide, and oxygen radicals were quantified using molecular probe 2′,7′-dichlorofluorescin diacetate. Results: Morphine (1 μM) or the selective δ-opioid receptor agonist BW373U86 (10 pM) given for 10 min before 1 h of ischemia and 3 h of reoxygenation reduced cell death (31 ± 5%, n = 6, and 28 ± 5%, n = 6 [P < 0.05], respectively, 53 ± 6%, n = 6, in controls) and generated oxygen radicals before ischemia (724 ± 53, n = 8, and 742 ± 75, n = 8 [P < 0.05], respectively, vs. 384 ± 42, n = 6, in controls, arbitrary units). The protection of morphine was abolished by naloxone, or the selective δ1-opioid receptor antagonist 7-benzylidenenaltrexone. Reduction in cell death and increase in oxygen radicals with BW373U86 were blocked by the selective mitochondrial KATP channel antagonist 5-hydroxydecanoate or diethyldithiocarbamic acid (1000 μM), which inhibited conversion of O2- to H2O2. The increase in oxygen radicals was abolished by the mitochondrial electron transport inhibitor myxothiazol. Reduction in cell death was associated with attenuated oxidant stress at reperfusion. Conclusion: Stimulation of δ1-opioid receptors generates oxygen radicals via mitochondrial KATP channels. This signaling pathway attenuates oxidant stress and cell death in cardiomyocytes.