title: Mechanisms of hydrogen-peroxide-induced biphasic response in rat mesenteric artery.
abstract: 1. In phenylephrine (PHE) (1 micro M)-precontracted superior mesenteric arteries from adult rats, low concentration of hydrogen peroxide (H(2)O(2), 10-100 micro M) caused only contraction, while high concentration of H(2)O(2) (0.3-1 mM) caused a biphasic response: a transient contraction followed by a relaxation response. 2. Endothelium removal did not affect the biphasic response. 7,7-Dimethyl-(5Z,8Z)-eicosadienoic acid, diclofenac, furegrelate, or SQ 29548 greatly inhibited the contraction but did not affect the relaxation. 17-Octadecynoic acid, eicosatriynoic acid, ICI 198615, SQ 22536, or ODQ did not inhibit the biphasic response. 3. KCl at 40 mM inhibited the relaxation response to H(2)O(2) by 98+/-24%. 4-Aminopyridine (4-AP) inhibited while tetraethylammonium chloride (TEA), charybdotoxin, or glibenclamide attenuated the relaxation response. A combination of 4-AP, TEA and glibenclamide mimicked the effects of 40 mM KCl. Iberiotoxin, apamin, or barium chloride did not inhibit the relaxation response. 4. H(2)O(2) at 1 mM hyperpolarized membrane potential and reversibly augmented K(+) current in smooth muscle cells of mesenteric artery. These effects of H(2)O(2) were attenuated significantly by 4-AP. 5. In summary, in PHE-precontracted rat mesenteric artery: (1) the response to H(2)O(2) shifted qualitatively from contraction to a biphasic response as H(2)O(2) increased to 0.3 mM or higher; (2) the relaxation response is caused by the activation of K(+) channels, with voltage-dependent K(+) channels playing a primary role; and the contraction is likely to be mediated by thromboxane A(2); (3) the K(+) channel activation by H(2)O(2) is independent of phospholipase A(2), cyclooxygenase, lipoxygenase, cytochrome P450 monooxygenase, adenylate or guanylate cyclase.
authors.affiliation: Department of Anaesthesia, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Yu-Jing
authors.initials: YJ
authors.lastname: Gao
authors.forename: Simon
authors.initials: S
authors.lastname: Hirota
authors.forename: Da-Wei
authors.initials: DW
authors.lastname: Zhang
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Janssen
authors.forename: Robert M K W
authors.initials: RM
authors.lastname: Lee
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D011921:Rats, Inbred WKY; D013928:Thromboxane A2 / Q000494:pharmacology; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D010656:Phenylephrine; D013928:Thromboxane A2; D006861:Hydrogen Peroxide