Apamin-sensitive, non-nitric oxide (NO) endothelium-dependent relaxations to bradykinin in the bovine isolated coronary artery: no role for cytochrome P450 and K+.
Since cytochrome P(450)-derived metabolites of arachidonic acid and K(+) have been implicated in endothelium-derived hyperpolarizing factor (EDHF)-dependent responses, the aim of this study was to determine whether such factors contribute to non-nitric oxide (NO), endothelium-dependent relaxation to bradykinin (BK) in bovine isolated coronary artery. In rings of artery contracted with U46619 and treated with indomethacin (3 microM) and N(G)-nitro-L-arginine (L-NOARG; 100 microM), relaxation to BK (0.01 nM-0.3 microM) was blocked by approximately 60% after inhibition of K(+) channels with either high extracellular K(+) (high [K(+)](o); 15 - 67 mM) or apamin (0.3 microM). Ouabain (1 microM), an inhibitor of Na(+)/K(+)-ATPase, decreased the sensitivity to BK without affecting the maximum response. In L-NOARG-treated rings, ouabain had no further effect on the relaxation to BK. An inhibitor of inward-rectifying K(+) channels, Ba(2+) (30 microM), had no effect on relaxations to BK in the absence or presence of either L-NOARG or ouabain. KCl (2.5 - 10 mM) elicited small relaxations ( approximately 20%) that were abolished by nifedipine (0.3 microM) and ouabain. Both the high [K(+)](o)/apamin-sensitive relaxation to BK, and the relaxation to the K(ATP) channel-opener, levcromakalim (0.6 microM), were unaffected by the cytochrome P(450) inhibitor, 7-ethoxyresorufin (10 microM), or by co-treatment with a phospholipase A(2) inhibitor, arachidonyl trifluoromethyl ketone (AACOCF(3); 3 microM) and a diacylglycerol (DAG)-lipase inhibitor, 1, 6-bis-(cyclohexyloximinocarbonylamino)-hexane (RHC 80267; 30 microM). The non-NO/high [K(+)](o)-insensitive, approximately 40% relaxation to BK was, however, abolished by these treatments. Therefore, neither cytochrome P(450)-derived metabolites of arachidonic acid nor K(+) appear to mediate the EDHF-like relaxation to BK (i.e the non-NO, high [K(+)](o)/apamin-sensitive component) in bovine coronary arteries. Cytochrome P(450)-derived metabolites may be released at higher BK concentrations to act in parallel with NO and the high [K(+)](o)/apamin-sensitive mechanism.
Drummond
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GR
Department of Pharmacology, Tri-radiate Building, University of Melbourne, Victoria 3010, Australia.
Selemidis
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Cocks
T M
TM
D000818:Animals; D001030:Apamin / Q000494:pharmacology*; D016718:Arachidonic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism; D001095:Arachidonic Acids / Q000494:pharmacology; D001685:Biological Factors / Q000502:physiology; D001920:Bradykinin / Q000494:pharmacology* / Q000502:physiology; D002417:Cattle; D003331:Coronary Vessels / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D019806:Cromakalim / Q000494:pharmacology; D003512:Cyclohexanones / Q000494:pharmacology; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism / Q000502:physiology*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D010078:Oxazines / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology
D001095:Arachidonic Acids; D001685:Biological Factors; D003512:Cyclohexanones; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010078:Oxazines; D011480:Protease Inhibitors; C067410:endothelium-dependent hyperpolarization factor; C081565:arachidonyltrifluoromethane; D019806:Cromakalim; D001030:Apamin; D016718:Arachidonic Acid; D009569:Nitric Oxide; C007649:ethoxyresorufin; D010042:Ouabain; D011189:Potassium Chloride; C036535:1,6-bis(cyclohexyloximinocarbonyl)hexane; D003577:Cytochrome P-450 Enzyme System; D011188:Potassium; D001920:Bradykinin