title: Beta-adrenergic receptors in guinea-pig liver plasma membranes and thermal lability of [3H]dihydroalprenolol binding sites.
abstract: beta-Adrenergic receptors in guinea-pig liver plasma membranes were characterized by radioligand binding, using l-[3H]dihydroalprenolol ([3H]DHA), l-3-[125I]iodocyanopindolol ([125I]CYP) and dl-[3H]4-(3-tertiarybutylamino-2-hydroxypropoxy)-benzimidazole-2- one hydrochloride [( 3H]CGP-12177). The binding of both [125I]CYP and [3H]CGP-12177 to membranes exhibited high affinity (Kd = 3.5 +/- 0.2 pM for [125I]CYP and 0.75 +/- 0.10 nM for [3H]CGP-12177) and stereospecificity; the maximal binding sites were 130 +/- 15 and 137 +/- 8 fmoles/mg protein respectively. Catecholaminergic agonists competed for these binding sites in the order l-isoproterenol greater than l-epinephrine greater than l-norepinephrine, which is typical for beta 2-adrenergic receptors. The binding data are supported by parallel experiments on adenylate cyclase activation by catecholamines, and on antagonism of this activation by beta 1- and beta 2-selective blockers. The binding of [3H]DHA was excessive (Bmax = 21.4 pmoles/mg protein), exhibited low affinity (Kd = 34.6 nM), and lacked stereospecificity. When liver membranes were incubated at 50 degrees for 40 min in the presence of an agonist, l-isoproterenol, the binding of [3H]DHA to the heat-treated membranes exhibited high affinity (Kd = 1.07 +/- 0.17 nM) and the Bmax was reduced to 139 +/- 22 fmoles/mg protein. In such membranes, as opposed to native membranes, stereospecificity was evident and catecholaminergic agonists competed for the binding sites in the order typical for beta 2-adrenergic receptors. However, agonist competition of the binding to the heat-treated membranes could not be modulated by guanine nucleotides, indicating a loss of communication between the receptor and the guanine nucleotide regulatory protein.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D000526:Alprenolol / Q000031:analogs & derivatives*; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D004082:Dihydroalprenolol / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D006358:Hot Temperature; D020120:Iodocyanopindolol; D007545:Isoproterenol / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D008297:Male; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011412:Propanolamines / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D037361:Adenylate Cyclase Toxin; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D006165:Guanylyl Imidodiphosphate; D004082:Dihydroalprenolol; D020120:Iodocyanopindolol; D000526:Alprenolol; D002772:Cholera Toxin; D010869:Pindolol; D007545:Isoproterenol; C033394:CGP 12177