title: [3H] norepinephrine binding by rat glial cells in culture. Lack of correlation between binding and adenylate cyclase activation.
abstract: Subcellular fractions prepared from rat glial cells in culture (clonal line c6) were used in an attempt to characterize the adrenergic receptor involved in adenylate cyclase activation. Both [3H] norepinephrine binding and enzyme activation were measured under identical experimental conditions. Binding sites for norepinephrine could be detected; their main characteristics were: apparant Km: 4 - 10-6 M, macimal capacity: 20 pmol/mg protein. Their stereospecificity towards structually related drugs was found to be different from the stereospecificity of the receptor involved in adenylate cyclase activation. Thus, 3-methoxydopamine (a competitive inhibitor of norepinephrine for adenylate cyclase activation), phenylephrine (a partial adrennergic agonist) and the blocking agent propranolol were unable to compete with [3H] norepinephrine for binding. On the other hand, several molecules like dopa bearing a catechol group and which are unable to interact with the adenylate cyclase as agonists or competitive inhibitors strongly inhibited [3H] norepinephrine binding. As in several other systems so far studied, the presence on the glial cell's membrane of a large number of "catechol-binding sites" makes it difficult to characterize the beta-adrenergic receptor.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002395:Catecholamines / Q000494:pharmacology; D002999:Clone Cells / Q000378:metabolism; D004789:Enzyme Activation; D009374:Neoplasms, Experimental / Q000378:metabolism; D009380:Neoplasms, Nerve Tissue / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D011941:Receptors, Adrenergic; D013329:Structure-Activity Relationship; D014316:Tritium
chemical_list: D002395:Catecholamines; D011941:Receptors, Adrenergic; D014316:Tritium; D000262:Adenylyl Cyclases; D009638:Norepinephrine