Expression and Characterization of the Rat D3 Dopamine Receptor: Pharmacologic Properties and Development of

A baculovirus expression system provided an enriched source of biologically and immunologically active D3 dopamine recep-tors. Receptors expressed in Spodoptera frugiperda insect (Sf9) cells at a density of 5 to 1 5 pmol/mg of protein displayed high affinity for the antagonists, eticlopride, fluphenazine and spiro-peridol, and the agonist, N-propylnorapomorphine. The binding of agonists was not sensitive to GTP. Antisera raised against synthetic peptides in the third intracellular loop of the D3 dopa-mine receptor immunoprecipitated binding sites for (S)-3-11 el]-iodo-2-hydroxy-5,6-dimethoxy-N-[(1-ethyl-2-pyrrolidinyl)-methyl]-benzamide from solubilized extracts of infected Sf9 cells and detergent extracts of rat caudate. These antisera specifically reco9nized a single band on immunoblots of Sf9 cells infected with recombinant D3 baculovirus. Both the immunoprecipitation and immunoblot reactions were blocked by preincubation of th