Beta3-adrenergic relaxation of bovine iris sphincter
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Published on: August 18, 2014
O Geyer1, A Bar-Ilan, R Nachman
1Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel.
Abstract:
Bovine iris sphincter in vitro responded to beta-adrenergic stimulation with pronounced relaxation (EC50 of isoproterenol = 0.3 nM), which was potentiated by the cAMP phosphodiesterase inhibitor, isobutylmethylxanthine, and mimicked by the adenylyl cyclase activator, forskolin. The beta1/beta2 antagonist, propranolol, exhibited low potency with calculated Ki of 200 nM. The beta3-selective antagonist, bupranolol, exhibited a biphasic inhibition profile, with calculated Kis of approximately 20-50 and 200-300 nM. The beta3-selective agonist, BRL 37344, elicited 70% of maximal relaxation (EC50 = 30 nM). When relaxation was induced by BRL 37344, bupranolol exhibited much higher potency (calculated Ki = 1 nM). Our data suggest that the beta-adrenergic relaxation response in bovine iris sphincter is mediated by a mixed population of beta-adrenergic receptors, with a predominant contribution of atypical, most likely beta3 subtype, receptors.
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