Opioids stimulate sarcolemmal NAD(P)H-vanadate dehydrogenase activity

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Abstract
The present study demonstrates that the bovine cardiac sarcolemma possesses an NAD(P)H dehydrogenase activity which is able to oxidize both NADH and NAD(P)H in the presence of vanadate as an electron acceptor. The NADH dehydrogenase activity was significantly higher than the NAD(P)H dehydrogenase activity and both of them were almost completely inhibited by superoxide dismutase and atebrin and markedly reduced by the addition of the protonophore 2,4-dinitrophenol. The incubation of the sarcolemma in the presence of 10−10, 10−9, 10−8 M methionine-enkephalin, a prevalent δ-opioid receptor agonist, or dynorphin A (1–17), a prevalent κ-receptor agonist, produced a dose-dependent increase in the NAD(P)H dehydrogenase activity, with 10−10 and 10−9 M dynorphin A (1–17) more effective than the corresponding doses of methionine-enkephalin. The preincubation of the sarcolemma in the presence of superoxide-dismutase, atebrin or 2,4-dinitrophenol strongly inhibited the opioid-stimulated dehydrogenase activity. The stimulatory action elicited by 10−8 M methionine-enkephalin or dynorphin A (1–17) was completely antagonized by 10−8 M naloxone or Mr 1452, respectively, whilst 10−8 M naloxone exerted only a partially antagonistic action against the effect produced by 10−8 M dynorphin A (1–17), significantly more accentuated than the action of 10−8 M Mr 1452 versus the same dose of methionine-enkephalin.