TY - JOUR T1 - Presence of Both <em>Beta</em><sub>1</sub>- and <em>Beta</em><sub>2</sub>-Adrenergic Receptors in a Single Cell Type JF - Molecular Pharmacology JO - Mol Pharmacol SP - 463 LP - 469 VL - 20 IS - 3 AU - VINCENT HOMBURGER AU - MARGUERITE LUCAS AU - ETELKA ROSENBAUM AU - GÉRARD VASSENT AU - JOËL BOCKAERT Y1 - 1981/11/01 UR - http://molpharm.aspetjournals.org/content/20/3/463.abstract N2 - Many tissues, including lung, heart, and brain, have been shown to contain beta1 and beta2-adrenergic receptor subtypes. This raises the question of whether receptor subtype heterogeneity corresponds to cell type heterogeneity within the tissue, or whether beta1- and beta2-receptors can coexist in the same cell. We have shown, by both radioligand binding studies and adenylate cyclase experiments, that these two receptor subtypes coexist in C6 cloned glioma cells and in three derived subclones. Competition experiments in binding and adenylate cyclase assays were conducted using membranes of C6 glioma cells and of three derived subclones. When [3H]dihydroalprenolol was used as the radioactive ligand, graphic and computer analysis of the competition binding curves obtained with beta1- or beta2-specific drugs always indicated a heterogeneity of beta-adrenergic receptors. For C6 glioma cell membranes, computer analysis indicated the presence of 80-90% beta1-receptors and 10-20% beta2-receptors. The same results were obtained with the three subclones. Analysis of the curves for the inhibition of isoproterenol-stimulated adenylate cyclase by practolol, a beta1-selective antagonist, showed the presence of two components. The heterogeneity of these practolol inhibition curves indicated that both types of beta-adrenergic receptors are coupled to the cyclase. Analysis of the dose-response curves of adenylate cyclase activation obtained with specific beta2-agonists also showed a heterogeneity of the response. This finding suggested that occupation of the beta2-receptors by a beta2-agonist was responsible for most of the cyclase activation and also that occupation of beta1-receptors by such an agonist can lead to stimulation of the enzyme but with a less efficient coupling. In conclusion, both beta1- and beta2-adrenergic receptors coupled to adenylate cyclase can coexist on a single cell. ACKNOWLEDGMENTS We are indebted to Miss Dreyfus and Mrs. du Parc for preparation of the manuscript. ER -