RT Journal Article SR Electronic T1 Isolation and Characterization of S49 Lymphoma Cells Deficient in β-Adrenergic Receptors: Relation of Receptor Number to Activation of Adenylate Cyclase JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 16 OP 27 VO 15 IS 1 A1 GARY L. JOHNSON A1 HENRY R. BOURNE A1 MARY K. GLEASON A1 PHILIP COFFINO A1 PAUL A. INSEL A1 KENNETH L. MELMON YR 1979 UL http://molpharm.aspetjournals.org/content/15/1/16.abstract AB Variant S49 lymphoma cells that have a diminished response to beta-adrenergic amines were selected from wild-type clones, using the beta-adrenergic agonist terbutaline in the presence of phosphodiesterase inhibitors. Variants (termed betap variants) having approximately 50% of wild-type beta-adrenergic receptors and 50% catecholamine-stimulated adenylate cyclase activity relative to wild-type were isolated in a single step selection. When these betap variants were mutagenized and subjected to a second round of selection with terbutaline and phosphodiesterase inhibitors, receptor deficient variants (termed betad) expressing 10-30% of wild-type beta-adrenergic receptors and responsiveness to isoproterenol were isolated. Two independent betap clones and the respective betad clones selected from them were characterized with respect to their adenylate cyclase and receptor properties. Both betap and betad variant cells demonstrated a diminished response to isoproterenol and an increased response to PGE1 relative to wild-type. Membranes from all four receptor-deficient clones responded normally to Gpp(NH)p, NaF, and PGE1. The density of beta-adrenergic receptors in membranes measured by the specific binding of [125I]IHYP was between 40 and 65%, relative to wild-type, for clones betap1 and betap2 and from 10 to 30% in betad1 and betad2. The dissociation constant for agonist and antagonist binding was the same for receptor-deficient and wild-type membranes. A direct relationship was obtained between beta-adrenergic receptor number and maximal activation of adenylate cyclase, indicating that beta-adrenergic receptor number limits the maximal activation of adenylate cyclase by catecholamines. These results conflict with the finding that isoproterenol stimulates S49 adenylate cyclase at concentrations well below those required to produce an equivalent fractional occupancy of receptors. The betap and betad phenotypes rule out an explanation of this discrepancy that depends on a number of receptors in excess of that required for maximal stimulation.