Morphine mimics preconditioning via free radical signals and mitochondrialK-ATP channels in myocytes

Background-We tried to determine whether morphine mimics preconditioning (P C) to reduce cell death in cultured cardiomyocytes and whether opioid delta (1) receptors, free radicals, and K-ATP channels mediate this effect. Methods and Results-Chick; embryonic ventricular myocytes were studied in a flow-through chamber while flow rate, pH, and O-2 and CO2 tension were con trolled. Cardiomyocyte viability was quantified with propidium iodide (5 mu mol/L), and production of free radicals was measured with 2',7'-dichlorofl uorescin diacetate. PC with 10 minutes of simulated ischemia before 10 minu tes of reoxygenation or morphine (1 mu mol/L) or BW373U86 (10 pmol/L) infus ion for 10 minutes followed by a 10-minute drug-free period before 1 hour o f ischemia and 3 hours of reoxygenation reduced cell death to the same exte nt (*P<0.05) (PC, 20+/-1%, n=7*; morphine, 32+/-4%, n=8*; BW373U86, 21+/-60 %; controls, 52+/-5%, n=8). Like PC, morphine and BW373U86 increased free r adical production 2-fold before ischemia (0.35+/-0.10, n=6*; 0.41+/-0.08, n =4* versus controls, 0.15+/-0.05, n=8, arbitrary units). Protection and inc reased free radical signals during morphine infusion were abolished with ei ther the thiol reductant 2-mercaptopropionyl glycine (400 <mu>mol/L), an an tioxidant; naloxone (10 mu mol/L), a nonselective morphine receptor antagon ist; BNTX (0.1 mu mol/L), a selective opioid delta (1) receptor antagonist; or 5-hydroxydecanoate (100 mu mol/L), a selective mitochondrial K-ATP chan nel antagonist. Conclusions-These results suggest that direct stimulation of cardiocyte opi oid delta (1) receptors leads to activation of mitochondrial K-ATP channels . The resultant increase of intracellular free radical signals may be an im portant component of the signaling pathways by which morphine mimics precon ditioning in cardiomyocytes.