The Effects of κ-Opioid Receptor Stimulation on Electrical Coupling during Ischemia in the Perfused Isolated Rat Heart.

Two series of experiments were performed in the perfused isolated rat heart to determine whether stimulation of κ-opioid receptor with U50,488H, a selective κ-opioid receptor agonist, produces any changes in electrical coupling during prolonged ischemia and whether these changes in electrical coupling is associated with the cardioprotection induced by U50,488H. It was found that U50,488H concentration dependently increased formazan content and reduced lactate dehydrogenase (LDH) release induced by 30 min of ischemia and 120 min of reperfusion, and the ameliorating effect of 10mol/L U50,488H was abolished by 5x10mol/L nor-binaltorphimine (nor-BNI), a selective Κ-opioid receptor antagonist, or 10mol/L 5-hydroxydecanoate (5-HD), a selective mitochondrial ATP-sensitive K(KATP) channels blocker. The onset of electrical uncoupling during prolonged ischemia was delayed by U50,488H, and delaying effect was not only abolished, but also advanced by nor-BNI or 5-HD compared with control group. These results demonstrate that delayed electrical uncoupling is associated with the cardioprotection induced by U50,488H. These effects of U50,488H are mediated by mitochondrial KATPchannels.