title: Pharmacological characterization of mammalian D1 and D2 dopamine receptors expressed in Drosophila Schneider-2 cells.
abstract: Mammalian D1 and D2 dopamine receptors were stably expressed in Drosophila Schneider-2 (S2) cells and screened for their pharmacological properties. Saturable, dose-dependent, high affinity binding of the D1-selective antagonist [3H]SCH-23390 was detected only in membranes from S2 cells induced to express rat dopamine D1 receptors, while saturable, dose-dependent, high affinity binding of the D2-selective antagonist [3H]methylspiperone was detected only in membranes from S2 cells induced to express rat dopamine D2 receptors. No specific binding of either radioligand could be detected in membranes isolated from uninduced or untransfected S2 cells. Both dopamine D1 and D2 receptor subtypes displayed the appropriate stereoselective binding of enantiomers of the nonselective antagonist butaclamol. Each receptor subtype also displayed the appropriate agonist stereoselectivities. The dopamine D1 receptor bound the (+)-enantiomer of the D1-selective agonist SKF38393 with higher affinity than the (-)-enantiomer, while the dopamine D2 receptor bound the (-)-enantiomer of the D2-selective agonist norpropylapomorphine with higher affinity than the (+)-enantiomer. At both receptor subtypes, dopamine binding was best characterized as occurring to a single low affinity site. In addition, the low affinity dopamine binding was also found to be insensitive to GTPgammaS and magnesium ions. Overall, the pharmacological profiles of mammalian dopamine D1 and D2 receptors expressed in Drosophila S2 cells is comparable to those observed for these same receptors when they are expressed in mammalian cell lines. A notable distinction is that there is no evidence for the coupling of insect G proteins to mammalian dopamine receptors. These results suggest that the S2 cell insect G system may provide a convenient source of pharmacologically active mammalian D1 and D2 dopamine receptors free of promiscuous G protein contaminants.
authors.affiliation: Department of Pharmacology, University of Mississippi, University, Mississippi 38677-1848, USA. john@olemiss.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Schetz
authors.forename: Ok-Jin
authors.initials: OJ
authors.lastname: Kim
authors.forename: David R
authors.initials: DR
authors.lastname: Sibley
mesh_terms: D000818:Animals; D002460:Cell Line; D018491:Dopamine Agonists / Q000378:metabolism / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000378:metabolism / Q000494:pharmacology; D004330:Drosophila; D005822:Genetic Vectors; D066298:In Vitro Techniques; D007700:Kinetics; D051381:Rats; D017447:Receptors, Dopamine D1 / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D011994:Recombinant Proteins