[3H]norepinephrine binding by rat glial cells in culture lack of correlation between binding and adenylate cyclase activation |
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Authors: | Joël Premont Philippe Benda Serge Jard |
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Affiliation: | Laboratoire de Physiologie Cellulaire, Collège de France 75231, Paris Cedex 05, France |
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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: apparent Km : 4 · 10−6 M, maximal 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 adrenergic 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 β-adrenergic receptor. |
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