Atypical SCH23390 Binding Sites Are Present on Bovine Adrenal Medullary Membranes |
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Authors: | Dahmer Mary K Senogles Susan E |
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Institution: | (1) Department of Biochemistry, College of Medicine, University of Tennessee, Memphis, Tennessee;(2) Department of Biochemistry, College of Medicine, University of Tennessee, Memphis, Tennessee |
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Abstract: | D1-selective dopamine receptor agonists inhibit secretagogue-stimulated catecholamine secretion from bovine adrenal chromaffin cells. The purpose of the studies reported here was to use the radiolabeled D1-selective dopamine receptor antagonist, SCH23390, to characterize putative D1-like dopamine receptors responsible for this effect. Characterization of SCH23390 binding sites demonstrated an unusual pharmacological profile inconsistent with classical D1-like receptors. 125I]SCH23390 bound to adrenal medullary membranes was competed for by non-radioactive iodo-SCH23390 (Kd = 490 ± 50 nM), but not by (+)butaclamol. Other classical D1 antagonists had little, if any, effect. Competition with dopamine receptor agonists demonstrated a relative rank order of potency profile characteristic of D1-like dopamine receptors, however, Kis were higher than those found in other tissues. The Kis for competition of 125I]SCH23390 binding by C1-APB and SKF38393 (16 and 118 M, respectively) are nearly identical to the IC50s previously observed for inhibition of secretion (9 and 100 M, respectively). Combined these data suggest that adrenal medullary membranes contain a novel SCH23390 binding site involved in the inhibition of secretion by D1-selective agonists. |
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Keywords: | Adrenal bovine catecholamines SCH23390 |
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