FUNCTIONAL COUPLING OF HUMAN D-2, D-3, AND D-4 DOPAMINE-RECEPTORS IN HEK293 CELLS

The D-2 dopamine receptor is known to be functionally coupled to the i nhibition of adenylate cyclase when expressed in a number of mammalian cell lines. However, functional coupling of the recently discovered D -3 and D-4 dopamine receptor subtypes has been more difficult to demon strate. In this study, human D-2, D-3 and D-4 receptors were stably ex pressed separately in human embryonic kidney cells (HEK 293). In these cells, activation of D-2, D-3 or D-4 receptors resulted in the inhibi tion of forskolin-stimulated adenylate cyclase activity in a dose resp onsive manner. This activation was prevented by pre-incubation of the cells expressing these receptors with the dopaminergic antagonist halo peridol. Radioligand binding studies using [H-3]spiperone confirmed th at the atypical neuroleptic clozapine has higher affinity for the huma n D-4 receptor than the D-3 or D-4 receptors, although only 6-fold hig her than the D-2 receptor in this study. In addition, ribonuclease pro tection studies demonstrated the presence of D-4 dopamine receptor mRN A in human brain regions.