Epinephrine Binding to the Catecholamine Receptor and Activation of the Adenylate Cyclase in Erythrocyte Membranes

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RESUMO

Turkey erythrocyte membranes showed specific binding of [3H]epinephrine. The concentration of hormone required for half-maximal binding (30 μM) was the same as that required for half-maximal activation of the adenylate cyclase located in the same membrane preparation. The binding reaction at 37°C reached completion during the first minute of incubation, which agrees well with the known rapidity of the biological response to catecholamines. Specific binding was abolished by heating the membranes 1 min at 100°C. Chromatography of the bound 3H, after its extraction from the membranes, indicated that the hormone had fully retained its chemical structure. Epinephrine binding was inhibited by the β-adrenergic blocking agent propranolol, which also inhibited the activation of adenylate cyclase by the hormone. The specificity of phenethylamine derivatives in displacing [3H]epinephrine from the binding sites showed that a typical catecholamine receptor was responsible for the binding. Displacement of the bound hormone by analogs lacking the catechol group was more extensive at 37°C than at 0°C. Some of the analogs that displaced epinephrine from the binding site caused only a feeble activation of the adenylate cyclase, but were able to inhibit the activation of the enzyme by epinephrine. Thus, binding to a catecholamine receptor on a membrane preparation is an essential, but insufficient, condition to elicit a response.

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