Adaptive changes in the number of Gs- and Gi-proteins underlie adenylyl cyclase sensitization in morphine-treated rat striatal neurons.
In the present study we investigated the possible role of changes in the number of membrane-bound G-proteins in the sensitization of dopamine D1 receptor-stimulated adenylyl cyclase, observed in primary cultures of rat striatal neurons chronically exposed to morphine. Whereas exposure of these neurons to 10 microM morphine for 7 days caused a profound increase in cyclic AMP production, induced by the dopamine D1 receptor agonist SKF 38393 (1 microM), Scatchard analysis of [125I]SCH 23982 binding to membrane preparations revealed that neither the Bmax nor the Kd values of dopamine D1 receptor binding sites were affected. Interestingly, immunoblotting experiments revealed an increase (of more than 50%) in the number of stimulatory G-proteins (G alpha s) in neurons displaying an enhanced adenylyl cyclase activity. In morphine-treated neurons, the number of inhibitory G-proteins (G alpha i) appeared to be slightly reduced (by about 16%). Moreover, the observation that cholera toxin (0.1 nM)-stimulated cyclic AMP production, unlike that induced by forskolin (1 microM), was enhanced in morphine-treated neurons, indicates a causal relationship between the reciprocal changes in G-protein number and the increase of dopamine D1 receptor-stimulated adenylyl cyclase activity. The possible role of these changes in G-protein number in the development of morphine tolerance and dependence is discussed.
Van Vliet
B J
BJ
Department of Pharmacology, Free University, Medical Faculty, Amsterdam, Netherlands.
Van Rijswijk
A L
AL
Wardeh
G
G
Mulder
A H
AH
Schoffelmeer
A N
AN
D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism; D004361:Drug Tolerance; D019204:GTP-Binding Proteins / Q000378:metabolism*; D051379:Mice; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000187:drug effects / Q000378:metabolism*
D017447:Receptors, Dopamine D1; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D009020:Morphine; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases