[3H]Fluphenazine binding to brain membranes: simultaneous measurement of D-1 and D-2 receptor sites.
[3H]Fluphenazine was used to label both D-1 and D-2 dopamine receptors in mouse striatal membranes. The D-1 and D-2 specific binding of [3H]fluphenazine was discriminated by the dopamine antagonists SCH-23390 (D-1 selective) and spiperone (D-2 selective). Saturation analyses of these two sites yielded a D-1 receptor density in mouse striatum of 1,400 fmol/mg of protein and a D-2 receptor density of 700 fmol/mg of protein. The affinity of [3H]fluphenazine for the D-2 site was slightly greater than for the D-1 site; the equilibrium dissociation constant (KD) was 0.7 versus 3.2 nM, respectively. Assay conditions are described that reduce nonspecific binding of [3H]fluphenazine to acceptable levels (35% of total binding at 1 nM [3H]fluphenazine). By comparison of displacement curves from a series of dopaminergic and nondopaminergic ligands, the pharmacological specificity of [3H]fluphenazine binding in mouse striatum was demonstrated to be dopaminergic. Only small amounts of dopamine-specific (apomorphine-sensitive) [3H]fluphenazine binding were found in other brain regions. However, chlorpromazine displaced considerable [3H]fluphenazine from all brain regions, including cerebellum, suggesting the presence of a [3H]fluphenazine binding site with a phenothiazine specificity.
D000818:Animals; D001058:Apomorphine / Q000378:metabolism; D001552:Benzazepines / Q000494:pharmacology; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism*; D005476:Fluphenazine / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013134:Spiperone / Q000494:pharmacology; D014018:Tissue Distribution
D001552:Benzazepines; D011954:Receptors, Dopamine; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013134:Spiperone; D001058:Apomorphine; D005476:Fluphenazine