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Title: Ascorbic acid enables reversible dopamine receptor /sup 3/H-agonist binding

The effects of ascorbic acid on dopaminergic /sup 3/H-agonist receptor binding were studied in membrane homogenates of bovine anterior pituitary and caudate, and rat striatum. In all tissues virtually no stereospecific binding (defined using 1uM (+)butaclamol) of the /sup 3/H-agonists N-propylnorapomorphine (NPA), apomorphine, or dopamine could be demonstrated in the absence of ascorbic acid. Although levels of total /sup 3/H-agonist binding were three to five times greater in the absence than in the presence of 0.1% ascorbic acid, the increased binding was entirely non-stereospecific. Greater amounts of dopamine-inhibitable /sup 3/H-NPA binding could be demonstrated in the absence of 0.1% ascorbic acid, but this measure of ''specific binding'' was demonstrated not to represent dopamine receptor binding since several other catecholamines and catechol were equipotent with dopamine and more potent than the dopamine agonist (+/-)amino-6,7-dihydroxy-1,2,3,4-tetrahydronapthalene (ADTN) in inhibiting this binding. High levels of dopamine-displaceable /sup 3/H-agonist binding were detected in fresh and boiled homogenates of cerebellum, an area of brain which receives no dopaminergic innervation, further demonstrating the non-specific nature of /sup 3/H-agonist binding in the absence of ascorbic acid. These studies emphasize that under typical assay conditions ascorbic acid is required in order to demonstrate reversible and specific /sup 3/H-agonist bindingmore » to dopamine receptors.« less
Authors:
; ; ;
Publication Date:
OSTI Identifier:
5800210
Resource Type:
Journal Article
Resource Relation:
Journal Name: Life Sci.; (United States); Journal Volume: 29:20
Research Org:
San Diego School of Medicine, La Jolla, CA
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; ASCORBIC ACID; RESPONSE MODIFYING FACTORS; DOPAMINE; STEREOCHEMISTRY; LIGANDS; RATS; RECEPTORS; TRACER TECHNIQUES; TRITIUM COMPOUNDS; UPTAKE; AMINES; ANIMALS; AROMATICS; AUTONOMIC NERVOUS SYSTEM AGENTS; CARDIOTONICS; CARDIOVASCULAR AGENTS; DRUGS; HYDROXY COMPOUNDS; ISOTOPE APPLICATIONS; LABELLED COMPOUNDS; MAMMALS; NEUROREGULATORS; ORGANIC COMPOUNDS; PHENOLS; POLYPHENOLS; RODENTS; SYMPATHOMIMETICS; VERTEBRATES; VITAMINS 550201* -- Biochemistry-- Tracer Techniques