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
-
Send reprint requests to: Katsutoshi Goto, Ph.D., Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, Ibaraki 305–8575, Japan.
-
↵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
- Received September 29, 1997.
- Accepted January 9, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|