title: Dopamine, acting through D-2 receptors, inhibits rat striatal adenylate cyclase by a GTP-dependent process.
abstract: This report demonstrates that the D-2 dopamine receptors that are present in rat striatum can directly inhibit the activity of adenylate cyclase in a GTP-dependent manner. N-n-propylnorapomorphine evoked a more pronounced inhibition than did dopamine. However, in the presence of the D-1-selective antagonist, SCH 23390, dopamine was also observed to inhibit the enzyme. Forskolin facilitated the detection of D-2 receptor-mediated inhibition by markedly stimulating striatal adenylate cyclase activity. The inhibition was antagonized in a dose-dependent manner by the D-2 receptor antagonist spiperone (Ki value = 70 pM) and was absolutely dependent on the presence of both GTP and sodium ions. Inhibition produced via D-2 receptors was additive with that produced via opiate or adenosine A1 receptors. The nonhydrolyzable GTP analogue, 5'-guanylylimidodiphosphate [Gpp(NH)p], did not substitute for GTP in promoting the D-2 receptor-mediated inhibition. It thus appears that D-2 receptors mediate adenylate cyclase inhibition by processes that have been observed for other neurotransmitters in the striatum and elsewhere. In addition, Gpp(NH)p displayed a Ca2+/calmodulin dependency for its inhibitory effects that was not shared by receptor-mediated, GTP-dependent inhibition.
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001058:Apomorphine / Q000031:analogs & derivatives / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects / Q000201:enzymology*; D000242:Cyclic AMP / Q000096:biosynthesis; D004298:Dopamine / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects*; D017448:Receptors, Dopamine D2
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001552:Benzazepines; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D006165:Guanylyl Imidodiphosphate; C009074:N-n-propylnorapomorphine; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D001058:Apomorphine; D002118:Calcium; D004298:Dopamine