Characterization of Endothelium-Dependent Relaxation Independent of NO and Prostaglandins in Guinea Pig Coronary Artery1
- Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8575, Japan.
Abstract
In the presence of Nω-nitro-l-arginine and indomethacin, acetylcholine (ACh) induced endothelium-dependent relaxation in guinea pig coronary artery preconstricted with 9,11-dideoxy-9α,11α-epoxymethano prostaglandin F2α. Dexamethasone and arachidonyltrifluoromethyl ketone, inhibitors of phospholipase A2, and 17-octadecynoic acid, an inhibitor of cytochrome P450 epoxygenase, had no effect on the response to ACh. Although proadifen, which is used widely as an inhibitor of cytochrome P450-dependent enzymes, suppressed the ACh-induced relaxation, the drug also inhibited the relaxation induced by cromakalim, a K+channel opener. In isolated smooth muscle cells of guinea pig coronary artery, proadifen, but not 17-octadecynoic acid, almost abolished delayed rectifier K+ current. Epoxyeicosatrienoic acids failed to relax the artery. Apamin and iberiotoxin, inhibitors of small- and large-conductance Ca++-activated K+channels, respectively, did not affect the relaxation induced by ACh. A combination of charybdotoxin plus apamin, but not iberiotoxin plus apamin, abolished the response. However, the combination of charybdotoxin plus apamin had no effect on ACh-induced increase in intracellular free Ca++ concentration in endothelial cells. These results suggest that epoxyeicosatrienoic acids do not contribute to Nω-nitro-l-arginine/indomethacin-resistant relaxation induced by ACh in the guinea pig coronary artery. The present study also proposes that K+ channels on vascular smooth muscle cells, which both charybdotoxin and apamin must affect for inhibition to occur, are the target for endothelium-derived hyperpolarizing factor.
Footnotes
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Send reprint requests to: Katsutoshi Goto, Ph.D., Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8575, Japan.
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↵1 This study was supported by a grant-in-aid for scientific research from the Ministry of Education, Science and Culture of Japan, and Uehara Memorial Foundation.
- Abbreviations:
- l-NNA
- Nω-nitro-l-arginine
- ACh
- acetylcholine
- NO
- nitric oxide
- ChTX
- charybdotoxin
- IbTX
- iberiotoxin
- 4-AP
- 4-aminopyridine
- 17-ODYA
- 17-octadecynoic acid
- TEA
- tetraethylammonium chloride
- EDHF
- endothelium-derived hyperpolarizing factor
- PLA2
- phospholipase A2
- EET
- epoxyeicosatrienoic acid
- U-46619
- 9,11-dideoxy-9α,11α-epoxymethano-prostaglandin F2α
- AACOCF3
- arachidonyltrifluoromethyl ketone
- BKca
- large-conductance Ca++-activated K+ channel
- SKca
- small-conductance Ca++-activated K+ channel
- KATP
- ATP-sensitive K+ channel
- Kdr
- delayed rectifier K+ channel
- IKca
- intermediate-conductance Ca++-activated K+channel
- EGTA
- ethyleneglycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid
- HEPES
- N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid
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- Received September 29, 1997.
- Accepted January 9, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
