The KCa channel as a trigger for the cardioprotection induced by kappa-opioid receptor stimulation -: its relationship with protein kinase C

1 We first determined whether the cardioprotection resulting from kappa opioid receptor (K-OR) stimulation was blocked by the K-Ca, channel inhibitor, paxilline (Pax), administered before or during ischaemic insults in vitro. 2 In isolated rat hearts, 30min of ischaemia and 120min of reperfusion induced infarction and increased lactate dehydrogenase (LDH) release. In isolated ventricular myocytes subjected to 5 min of metabolic inhibition and anoxia followed by 10 min of reperfusion, the percentage of live cells and the amplitude of the electrically induced intracellular Ca2+ ([Ca2+](i)) transient decreased, while diastolic [Ca2+]i increased. Pretreatment with 10 mu M U50,488H, a K-OR agonist, attenuated the undesirable effects of ischaemic insults in both preparations. The beneficial effects Of kappa-OR stimulation, that were abolished by 5 mu M nor-BNI, a kappa-OR antagonist, were also abolished by 1 Pm Pax administered before ischaemic insults or 20 mu M atractyloside, an opener of the mitochondrial permeability transition pore. 3 Activation of protein kinase C (PKC) with 0.1 mu M phorbol 12-myristate 13-acetate decreased the infarct size and LDH release in isolated rat hearts subjected to ischaemia/reperfusion, and these effects were abolished by blockade of PKC with its inhibitors, 10 mu M GF109203X or 5 mu M chelerythrine, and more importantly by 1 mu M Pax. On the other hand, the cardioprotective effects of opening the K-Ca channel with 10 mu M NS 1619 were not altered by either PKC inhibitor. 4 In conclusion, the high-conductance K-Ca, channel triggers cardioprotection induced by K-OR stimulation that involves inhibition of MPTP opening. The K-Ca channel is located downstream of PKC.