title: ACh-induced relaxations of rabbit small mesenteric arteries: role of arachidonic acid metabolites and K+.
abstract: ACh-induced endothelium-dependent relaxation in rabbit small mesenteric arteries is resistant to N-nitro-L-arginine (L-NA) and indomethacin but sensitive to high K+, indicating the relaxations are mediated by endothelium-derived hyperpolarizing factors (EDHFs). The identity of the EDHFs in this vascular bed remains undefined. Small mesenteric arteries pretreated with L-NA and indomethacin were contracted with phenylephrine. ACh (10(-10) to 10(-6) M) caused concentration-dependent relaxations that were shifted to the right by lipoxygenase inhibition and the Ca(2+)-activated K+ channel inhibitors apamin (100 nM) or charybdotoxin (100 nM) and eliminated by the combination of apamin plus charybdotoxin. Relaxations to ACh were also blocked by a combination of barium (200 microM) and apamin but not barium plus charybdotoxin. Addition of K+ (10.9 mM final concentration) to the preconstricted arteries elicited small relaxations. K+ addition before ACh restored the charybdotoxin-sensitive component of relaxations to ACh. K+ (10.9 mM) also relaxed endothelium-denuded arteries, and the relaxations were inhibited by barium but not by charybdotoxin and apamin. With the use of whole cell patch-clamp analysis, ACh (10(-7) M) stimulated voltage-dependent outward K+ current from endothelial cells, which was inhibited by charybdotoxin, indicating K+ efflux. Arachidonic acid (10(-7) to 10(-4) M) induced concentration-related relaxations that were inhibited by apamin but not by charybdotoxin and barium. Addition of arachidonic acid after K+ (10.9 mM) resulted in more potent relaxations to arachidonic acid compared with control without K+ (5.9 mM). These findings suggest that, in rabbit mesenteric arteries, ACh-induced, L-NA- and indomethacin-resistant relaxation is mediated by endothelial cell K+ efflux and arachidonic acid metabolites, and a synergism exists between these two separate mechanisms.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
authors.forename: David X
authors.initials: DX
authors.lastname: Zhang
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Gauthier
authors.forename: Yuttana
authors.initials: Y
authors.lastname: Chawengsub
authors.forename: William B
authors.initials: WB
authors.lastname: Campbell
mesh_terms: D000109:Acetylcholine / Q000008:administration & dosage*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000008:administration & dosage; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011817:Rabbits; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D016718:Arachidonic Acid; D000109:Acetylcholine; D011188:Potassium