title: In situ molecular size of agonist dopamine D-2 binding sites in rat striatum.
abstract: Specific binding of [3H]N-propylnorapomorphine [( 3H]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 [3H]NPA binding was spiroperidol greater than or equal to NPA greater than LY 171555 greater than SCH 23390 greater than 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 nM, 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 [3H]spiroperidol binding to dopamine receptors. Irradiation inactivation of frozen whole rat striata showed a monoexponential loss of [3H]NPA binding sites without a change in the binding affinity. The target size of the [3H]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 [3H]spiroperidol (target size, 137,000 daltons).
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D013134:Spiperone / Q000378:metabolism
chemical_list: D011954:Receptors, Dopamine; D012965:Sodium Chloride; D013134:Spiperone; C009074:N-n-propylnorapomorphine; D006160:Guanosine Triphosphate; D001058:Apomorphine; D004298:Dopamine