title: Agonist binding to mammalian beta 1 and beta 2 adrenoceptors: modulation by guanine nucleotides and magnesium.
abstract: Agonist interaction with beta 1 and beta 2 adrenoceptors in rat and rabbit lung has been examined using ligand binding techniques and the results are discussed in relation to current models of beta-adrenoceptor-adenylate cyclase coupling. Agonist binding has been assessed by examining the ability of isoprenaline or salbutamol to displace the labelled antagonist 3H-dihydroalprenolol (3H-DHA) from specific receptor sites. Beta 1 and beta 2 adrenoceptors, even within the same tissue, exhibited different ion and temperature requirements for guanine nucleotide modulation of agonist binding. Thus, in contrast to the situation at beta 2 sites, agonist binding to beta 1 adrenoceptors was only sensitive to GTP if incubations were performed at physiological temperatures in the presence of Mg++ ions. These findings suggest that there may be different receptor-effector coupling relationships between the two beta-adrenoceptor subtypes.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000378:metabolism*; D000420:Albuterol / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004082:Dihydroalprenolol / Q000378:metabolism; D006150:Guanine Nucleotides / Q000502:physiology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D008274:Magnesium / Q000502:physiology*; D008297:Male; D011433:Propranolol / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D000318:Adrenergic beta-Agonists; D006150:Guanine Nucleotides; D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; D011433:Propranolol; D008274:Magnesium; D007545:Isoproterenol; D000420:Albuterol