Further characterization of the D 2 dopamine receptor expressed in MMQ cells

Abstract

The D 2 dopamine receptor expressed in the MMQ cell line was characterized by saturation binding using the D 2 dopamine radioligand [ 3H]spiperone. The K D for spiperone was 41 pM and the B max for these sites was 34 fmol/mg protein. Inhibition of forskolin-stimulated cAMP accumulation occurred in response to a variety of D 2 agonists, and the agonist effects were reversed by D 2 antagonists. Pertussis toxin pretreatment abolished agonist inhibition of cAMP accumulation. In addition, the α 2-adrenergic agonist UK 14304 inhibited cAMP accumulation; this effect was reversed by an α 2-adrenergic antagonist but not by a D 2 antagonist, indicating the presence of α 2-adrenergic receptors on these cells. Specific oligonucleotide primers were used in the polymerase chain reaction to determine, by restriction enzyme analysis and Southern blotting, that the long form of the two alternatively spliced variants of the D 2 dopamine receptor was the predominant variant expressed in these cells.