Diminution of contractile response by kappa-opioid receptor agonists in isolated rat ventricular cardiomyocytes is mediated via a pertussis toxin-sensitive G protein.
Opioids directly decrease the contractile response of isolated ventricular cardiomyocytes to electrical stimulation. To investigate whether these effects are mediated via GTP-binding G(i/o) proteins we examined the influence of pertussis toxin on the effects of the kappa-opioid receptor agonist trans-(+/-)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benz eneacetamide (U-50,488) methanesulphonate and on the as yet undescribed effects of the opioid peptide dynorphin A (1-8) on contraction. In isolated, electrically driven, rat ventricular cardiomyocytes both agents concentration dependently reduced cell shortening within 15 min, decreasing the contractile response by 79+/-4% (n=5) and 62+/-2% (n=6) of control values at maximal effective concentrations of 10 microM (U-50,488) and 1 microM [dynorphin A (1-8)], respectively. Pertussis toxin pre-treatment (200 ng/ml; 4.5-5 h) completely abolished the effects of U-50,488 and dynorphin A (1-8) on the contractile response, indicating that these effects are mediated via G(i/o) proteins. In addition, the non-selective opioid receptor antagonist (-)-naloxone and the kappa-opioid receptor antagonist nor-binaltorphimine antagonized the effects of U-50,488 and dynorphin A (1-8) on the contractile response. Furthermore, the mu- and delta-opioid receptor agonist (D-Ala2, D-Leu5)-enkephalin (DADLE) had no effects on contraction. These results indicate that the decrease in cell shortening is due to stimulation of kappa-opioid receptors. The direct effect of kappa-opioid receptor agonists on the contractile response thus represents an additional mechanism for decreasing cardiac contractility, besides the M-cholinoceptor- or adenosine receptor-mediated pathway. It is conceivable that increased release of endogenous dynorphins from the heart during hypoxia may protect the heart in a similar manner to adenosine.
Rudolf-Buchheim-Institut für Pharmakologie der Justus-Liebig-Universität Giessen, Germany.
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Wenzlaff
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Stein
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Teschemacher
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D004347:Drug Interactions; D004399:Dynorphins / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000187:drug effects*; D006352:Heart Ventricles / Q000187:drug effects; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010446:Peptide Fragments / Q000494:pharmacology*; D037342:Pertussis Toxin; D051381:Rats; D017208:Rats, Wistar; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D000959:Antihypertensive Agents; D010446:Peptide Fragments; D017473:Receptors, Opioid, kappa; D010566:Virulence Factors, Bordetella; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D004399:Dynorphins; C026770:dynorphin (1-8); D037342:Pertussis Toxin; D019204:GTP-Binding Proteins