title: Characterization of [125I](R)-trans-7-hydroxy-2-[N-propyl-N-(3'-iodo-2'-propenyl)amino] tetralin binding to dopamine D3 receptors in rat olfactory tubercle.
abstract: [125I](R,S)-trans-7-Hydroxy-2-[N-propyl-N-(3'-iodo-2'-propenyl)- amino]tetralin ([125](R,S)-trans-7-OH-PIPAT) has been shown to bind with high affinity to dopamine D3 receptors expressed in Spodoptera frugiperda cells. No specific binding was seen in Spodoptera frugiperda cells expressing a high density of D2 receptors. It was therefore, suggested that [125I] (R,S)-trans-7-OH-PIPAT selectively labels D3 receptors. In the present study, saturation binding of [125I](R)-trans-7-OH-PIPAT to membranes from rat olfactory tubercle resulted in markedly curvilinear Scatchard plots, suggesting that the radioligand was binding to more than one receptor class or affinity state. [125I] (R)-trans-7-OH-PIPAT bound with high affinity to membranes from human embryonic kidney-293 cells expressing transfected D2 or D3 receptors and to membranes from Chinese hamster ovary cells expressing serotonin1A receptors. Binding of [125I](R)-trans-7-OH-PIPAT to serotonin1A and D2 receptors was decreased or eliminated in the presence of NaCl and/or guanylyl-imidodiphosphate [Gpp(NH)p]. In the presence of Gpp(NH)p and NaCl, a linear Scatchard plot with a Kd value of 0.4 nM and a density of 100 fmol/mg of protein was obtained in membranes from rat olfactory tubercle. Agonists and antagonists inhibited binding of [125I](R)-trans-7-OH-PIPAT with a rank order of potency consistent with an interaction at D3 receptors. These results suggest that, in the presence of Gpp(NH)p and NaCl, [125I](R)-trans-7-OH-PIPAT specifically labels D3 receptors.
authors.affiliation: Department of Pharmacology, University of Pennsylvania, Philadelphia.
authors.forename: K D
authors.initials: KD
authors.lastname: Burris
authors.forename: T M
authors.initials: TM
authors.lastname: Filtz
authors.forename: S
authors.initials: S
authors.lastname: Chumpradit
authors.forename: M P
authors.initials: MP
authors.lastname: Kung
authors.forename: C
authors.initials: C
authors.lastname: Foulon
authors.forename: J G
authors.initials: JG
authors.lastname: Hensler
authors.forename: H F
authors.initials: HF
authors.lastname: Kung
authors.forename: P B
authors.initials: PB
authors.lastname: Molinoff
mesh_terms: D000818:Animals; D002460:Cell Line; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D009833:Olfactory Pathways / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011954:Receptors, Dopamine / Q000235:genetics / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000378:metabolism; D050637:Receptors, Dopamine D3; D011985:Receptors, Serotonin / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013764:Tetrahydronaphthalenes / Q000378:metabolism*; D014162:Transfection
chemical_list: C493593:DRD3 protein, human; C493595:Drd3 protein, rat; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D011985:Receptors, Serotonin; D013764:Tetrahydronaphthalenes; C081289:7-hydroxy-2-(N-n-propyl-N-(3-iodo-2'-propenyl)-amino)tetralin; D006165:Guanylyl Imidodiphosphate; D012965:Sodium Chloride