N. Ozaki et al., DOPAMINE D-1 AND D-2 RECEPTORS AND THEIR SIGNAL SYSTEM PRESENT IN COATED VESICLES PREPARED FROM BOVINE STRIATAL TISSUE, Journal of neurochemistry, 62(2), 1994, pp. 582-591
Coated vesicles (CVs) isolated from bovine striatal tissue were examin
ed to determine whether they are associated with dopamine signal syste
ms consisting of dopamine D-1 and D-2 receptors, G proteins, and adeny
late cyclase. Dopamine receptors in CVs were characterized by a dopami
ne D-1 receptor antagonist, [H-3]SCH 23390, and a dopamine D-2 recepto
r antagonist, [H-3]-spiroperidol. The bindings of both ligands were sp
ecifically saturable and reversible with a dissociation constant (K-D)
of 0.65 and 0.5 nM, respectively. Dopaminergic antagonists and agonis
ts inhibited the specific bindings of [H-3]SCH 23390 and [H-3]spiroper
idol in a stereoselective and concentration-dependent manner with an a
ppropriate rank order potency for dopamine D-1 or D-2 receptors. The r
egulations of the agonist binding by guanyl-5-ylimidodiphosphate were
observed. ADP ribosylation of the CVs with [P-32]NAD demonstrated pred
ominant labeling of bands of M(r) 47,000-52,000, 42,000-45,000, and 40
,000-39,000, which corresponded to the known molecular weights of the
alpha subunits of G(s) and G(i) proteins. The presence of alpha and be
ta subunits of G proteins in the CVs was also confirmed by immunoblott
ing assay. Adenylate cyclase activity, which was stimulated by SKF 383
93 and inhibited by dopamine D-2 receptor agonists, was present in the
CVs. These findings suggest that the dopamine D-1 and D-2 receptors i
n the CVs couple with adenylate cyclase via G(s)/G(i) protein.