title: Beta-adrenoceptor-mediated relaxation inhibited by tetrapentylammonium ions in rat mesenteric artery.
abstract: The aim of this study was to examine the contribution of K+ channel activation to beta-adrenoceptor-mediated relaxation in rat mesenteric arteries. Isoprenaline and fenoterol concentration-dependently relaxed the phenylephrine-preconstricted endothelium-intact arteries of the rat with EC50 values of 0.26 +/- 0.03 microM and 0.87 +/- 0.12 microM, respectively. Beta-adrenoceptor-mediated relaxation was significantly attenuated upon removal of endothelium. Tetrapentylammonium ions (TPA+) at low concentrations (1-5 microM) inhibited relaxations induced by beta-adrenoceptor agonists in arteries with and without endothelium, while glibenclamide (3 microM) had no effect. TPA+ (5 microM) inhibited isoprenaline-induced relaxation in the presence of either iberiotoxin (100 nM) or glibenclamide (3 microM). TPA+ did not alter forskolin-induced relaxation. In the presence of 60 mM extracellular K+, the relaxations induced by two agonists were reduced in endothelium-intact arteries and abolished in endothelium-denuded arteries. The present results suggest that the activation of TPA+-sensitive K+ channels contributes toward the relaxations mediated through beta- and beta2-adrenoceptor stimulation in rat mesenteric arteries.
authors.affiliation: Department of Physiology, Chinese University of Hong Kong, Shatin, NT. yu-huang@cuhk.edu.hk
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: K H
authors.initials: KH
authors.lastname: Kwok
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D005280:Fenoterol / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000502:physiology*
chemical_list: D000318:Adrenergic beta-Agonists; D010455:Peptides; D000644:Quaternary Ammonium Compounds; D011943:Receptors, Adrenergic, beta; D005280:Fenoterol; C064719:iberiotoxin; C027435:tetrapentylammonium; D007545:Isoproterenol; D011188:Potassium; D005905:Glyburide