title: Hyperpolarization of murine small caliber mesenteric arteries by activation of endothelial proteinase-activated receptor 2.
abstract: Activation of endothelial proteinase-activated receptor 2 (PAR-2) relaxes vascular smooth muscle (VSM) and causes hypotension by nitric oxide (NO)-prostanoid-dependent and -independent mechanisms. We investigated whether endothelium-dependent hyperpolarization of VSM was the mechanism whereby resistance caliber arteries vasodilated independently of NO. VSM membrane potentials and isometric tension were measured concurrently to correlate the electrophysiological and mechanical changes in murine small caliber mesenteric arteries. In uncontracted arteries, the PAR-2 agonist, SLIGRL-NH2 (0.1 to 10 micromol/L), hyperpolarized the VSM membrane potential only in endothelium-intact arterial preparations. This response was unaltered by treatment of arteries with inhibitors of NO synthases (L-NAME), soluble guanylyl cyclase (ODQ), and cyclooxygenases (indomethacin). L-NAME, ODQ, and indomethacin also failed to inhibit SLIGRL-NH2-induced hyperpolarization and of cirazoline-contracted mesenteric arteries. However, in blood vessels that were depolarized and contracted with 30 mmol/L KCl, the effects of the SLIGRL-NH2 on membrane potential and tension were not observed. SLIGRL-NH2-induced hyperpolarization and relaxation was inhibited completely by the combination of apamin plus charybdotoxin, but only partially inhibited after treatment with the combination of barium plus ouabain, suggesting an important role for SKCa and IKCa channels and a lesser role for Kir channels and Na+/K+ ATPases in the hyperpolarization response. We concluded that activation of endothelial PAR-2 hyperpolarized the vascular smooth muscle (VSM) cells of small caliber arteries, without requiring the activation of NO synthases, cyclooxygenases, or soluble guanylyl cyclase. Indeed, this hyperpolarization may be a primary mechanism for PAR-2-induced hypotension in vivo.
authors.affiliation: Smooth Muscle Research Group, Canadiian Institutes of Health Research Group on the Regulation of Vascular Contractility, Department of Pharmacology, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada. mcguire@mun.ca
authors.forename: John J
authors.initials: JJ
authors.lastname: McGuire
authors.forename: Morley D
authors.initials: MD
authors.lastname: Hollenberg
authors.forename: Brian M
authors.initials: BM
authors.lastname: Bennett
authors.forename: Chris R
authors.initials: CR
authors.lastname: Triggle
mesh_terms: D000818:Animals; D016764:Cell Polarity / Q000187:drug effects; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000166:cytology* / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology; D011453:Prostaglandins / Q000502:physiology; D044464:Receptor, PAR-2 / Q000187:drug effects*; D017461:Receptors, Atrial Natriuretic Factor / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: D026902:Potassium Channel Blockers; D024661:Potassium Channels, Inwardly Rectifying; D011453:Prostaglandins; D044464:Receptor, PAR-2; D009569:Nitric Oxide; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D017461:Receptors, Atrial Natriuretic Factor; C073616:atrial natriuretic factor receptor C; D000254:Sodium-Potassium-Exchanging ATPase