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In Situ Molecular Size of Agonist Dopamine D‐2 Binding Sites in Rat Striatum
Author(s) -
Gredal Ole,
Nielsen Mogens
Publication year - 1987
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1987.tb04102.x
Subject(s) - striatum , dopamine , agonist , chemistry , dopamine agonist , in situ , neuroscience , medicine , biology , biochemistry , receptor , dopaminergic , organic chemistry
Specific binding of [ 3 H] N ‐propylnorapomorphine ([ 3 H]NPA) to 3,4‐dihydroxyphenylethylamine (dopamine) D‐2 receptors was investigated in rat striatum in vitro. For various dopamine receptor substances, the rank order of potency to inhibit [ 3 H]NPA binding was spiroperidol ≧NPA ≥ LY 171555 ≥ SCH 23390 ≥ SKF 38393. A single high‐affinity binding site was found in membranes prepared in either Tris‐citrate buffer or imidazole buffer; the affinity constants were 0.11 and 0.76 n M , respectively. The number of receptors (33 pmol/g wet weight) was independent of whether the membranes were prepared in Tris‐citrate buffer or imidazole buffer and was similar to the number of receptors estimated by [ 3 H]spiroperidol binding to dopamine receptors. Irradiation inactivation of frozen whole rat striata showed a monoexponential loss of [ 3 H]NPA binding sites without a change in the binding affinity. The target size of the [ 3 H]NPA binding site was 81,000 daltons, which shows that the functional molecular entity to bind the dopamine D‐2 agonist was smaller than the molecular entity to bind the dopamine D‐2 antagonist [ 3 H]spiroperidol (target size, 137,000 daltons).