title: Characterization of a beta-adrenergic receptor in porcine trachealis muscle.
abstract: To establish a model of airway smooth muscle function we studied binding of [3H]dihydroalprenolol [( 3H]DHA), a beta-adrenergic antagonist, to membrane preparations of porcine trachealis muscle and investigated the response of adenylate cyclase to l-isoproterenol in tissue and plasma membranes. [3H]DHA binding was of high affinity (Kd = 1.0 +/- 0.1 nM), was saturable (Bmax = 87.6 +/- 13.2 fmol/mg protein), and was 90% beta 2 and 10% beta 1. Adenylate cyclase activity in the membrane preparation was (in pmol.10 min-1.mg protein-1 +/- SE): basal 420 +/- 74, guanosine 5'-triphosphate (GTP) (10 micron) 600 +/- 45, GTP (10 microM) + l-isoproterenol (100 microM) 660 +/- 63, NaF (10 mM) 1,500 +/- 134, and forskolin (100 microM) 3,000 +/- 410. Guanosine 5'-diphosphate (GDP) and GTP were active cofactors; l-isoproterenol appeared to function as an effector exchanging GTP for GDP on the guanine nucleotide regulatory protein. There was close agreement of the effective dose (ED50) of the l-isoproterenol-induced relaxation (0.95 +/- 0.45 microM) and the inhibitory constant of l-isoproterenol binding (0.39 +/- 0.10 microM). l-Isoproterenol (100 microM) induced a 100% increase in adenosine 3',5'-cyclic monophosphate (cAMP) levels in tissue strips over basal activity. Investigation of the difference in adenylate cyclase activity between tissue and plasma membranes revealed that l-isoproterenol responsive adenylate cyclase was diminished after initial homogenization. Electron microscopy demonstrated disruption of all cells at this early stage of preparation. The decrease in l-isoproterenol responsive adenylate cyclase following cell rupture is different from other tissues and suggests a difference in the actions of beta-agonist in smooth muscle compared with other tissues.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004082:Dihydroalprenolol / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006157:Guanosine Monophosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D013268:Stimulation, Chemical; D013552:Swine; D014132:Trachea / Q000378:metabolism*
chemical_list: D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; D006157:Guanosine Monophosphate; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D007545:Isoproterenol