Purification of the D-2 Dopamine Receptor and Characterization of Its Signal Transduction Mechanism

Abstract

Dopaminergic pathways appear to be involved in many brain functions including motoric, mental and emotional states. Dopamine is also associated with controlling pituitary prolactin and α melanocyte-stimulating hormone release. Dopamine receptors have been divided into D-l and D-2 subclasses according to their relationship to the adenylate cyclase system and their affinity for dopaminergic agonists and antagonists (reviewed in Seeman, 1980; Niznik, 1987). The D-l receptor stimulates adenylate cyclase and is virtually insensitive to substituted benzamide neuroleptics, whereas the D-2 receptor inhibits adenylate cyclase activity and has picomolar or nanomolar affinities for all neuroleptics. The D-2 receptor has been solubilized from membranes of pituitary gland and striatum by use of various detergents, and its pharmacology is well defined. This receptor is a glycoprotein as indicated by its specific adsorption to and elution from wheat germ agglutinin-Sepharose. Photoaffinity labeling of the D-2 dopamine receptor has indicated that, in a variety of mammalian tissues and species, a 92–94 kDa polypeptide is probably the ligand binding unit of the receptor (Lew et al.,1985; Amlaiky and Caron, 1986; Kanety and Fuchs, 1988). In order to elucidate the molecular mechanisms by which dopaminergic signal transduction correlates with dopaminergic functions, it is essential to isolate and fully characterize this receptor.