Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes: sulpiride lack of interactions with positive cooperative [3H]apomorphine binding.
Effects of dopaminergic agonists and antagonists on [3H]apomorphine binding to striatal membranes of rat brain was examined. Haloperidol and spiroperidol exhibited biphasic inhibition of [3H]apomorphine binding; one of which had the Hill coefficient of 0.9, whereas the other had that of 0.4. The former accounted for 65% of [3H]apomorphine binding while the latter consisted of 35% of the binding. Furthermore, the latter disappeared after kainic acid lesions. On the other hand, sulpiride and metoclopramide reduced [3H]apomorphine binding to 31% with the Hill coefficient of 0.9. The inhibition of [3H]apomorphine binding with the Hill coefficient of 0.4 which was shown by haloperidol and spiroperidol was not observed for sulpiride and metoclopramide. Previously, we demonstrated non- and positive-cooperative [3H]apomorphine binding to stiatal membranes. In the present study, it has been also shown that sulpiride inhibits non-cooperative [3H]apomorphine binding leaving that with allosteric properties unaffected. No inhibition of dopamine-sensitive adenylate cyclase was observed by 10(-4) M sulpiride while 90% inhibition was obtained with 10(-5) M haloperidol. From those results, it is suggested that non-cooperative [3H]spomorphine binding is not coupled with dopamine-sensitive adenylate cyclase.
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001058:Apomorphine / Q000378:metabolism*; D001667:Binding, Competitive; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism*; D006220:Haloperidol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D051381:Rats; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D013469:Sulpiride / Q000494:pharmacology*; D014316:Tritium
D011954:Receptors, Dopamine; D014316:Tritium; D013469:Sulpiride; D000262:Adenylyl Cyclases; D006220:Haloperidol; D001058:Apomorphine