Dopamine D₁ and D₂ Receptors and Their Signal System Present in Coated Vesicles Prepared from Bovine Striatal Tissue

Abstract

Coated vesicles (CVs) isolated from bovine striatal tissue were examined to determine whether they are associated with dopamine signal systems consisting of dopamine D, and D Z receptors, G proteins, and adenylate cyclase . Dopamine receptors in CVs were characterized by a dopamine D, receptor antagonist, [3 H]SCH 23390, and a dopamine D2 receptor antagonist, [ 3 H]spiroperidol . The bindings of both ligands were specifically saturable and reversible with a dissociation constant (K p) of 0 .65 and 0 .5 nM, respectively . Dopaminergic antagonists and agonists inhibited the specific bindings of [ 3H]SCH 23390 and [3 H]spiroperidol in a stereoselective and concentration-dependent manner with an appropriate rank order potency for dopamine D, or D 2 receptors . The regulations of the agonist binding by guanyl-5-ylimidodiphosphate were observed . ADP ribosylation of the CVs with [32 P]NAD demonstrated predominant labeling of bands of M, 47,000-52,000, 42,000-45,000, and 40,000-39,000, which corresponded to the known molecular weights of the a subunits of GS and G ; proteins . The presence of a and ß subunits of G proteins in the CVs was also confirmed by immunoblotting assay . Adenylate cyclase activity, which was stimulated by SKF 38393 and inhibited by dopamine D Z receptor agonists, was present in the CVs . These findings suggest that the dopamine D,

Effects of D1‐ and D2‐dopamine receptor activation on melatonin synthesis in bovine pinealocytes

“…[11] have shown that the density order of the receptors was dopamine D 1 > α 1 adrenergic > dopamine D 2 ≥ β 1 adrenergic receptors. This dopaminergic control has been also demonstrated in other tissue, for example, SKF‐38393, a D 1 ‐receptor agonist stimulated adenylate cyclase activity in coated vesicles isolated from bovine striatal tissues and inhibited by dopamine D 2 ‐receptor agonists [25]. Furthermore, functional interaction between melatonin and dopamine D 1 ‐receptors was reported in the retina [26], which indicated a link through the intracellular cyclic AMP system.…”