Functional coupling of dopamine D2 and muscarinic cholinergic receptors to their respective G proteins assessed by agonist-induced activation of high-affinity GTPase activity in rat striatal membranes.
Agonist-induced high-affinity GTPase activity was investigated using the crude membrane preparation from rat striatum. High-affinity GTPase activity was stimulated by dopamine and carbachol in a Mg(2+)-dependent manner and with possible optimum NaCl concentrations of 50-100 mM to detect the percent increase induced by each agonist. Dopamine and selective (as well as non-selective) D2 receptor agonists, but not selective D1 receptor agonists, stimulated activity in a concentration-dependent manner, with affinities which were significantly correlated with those for adenylate cyclase inhibition as previously reported in the literature. Maximal percent stimulation above basal high-affinity GTPase activity was 9.8 +/- 0.6% and 4.4-7.6% for dopamine and other synthetic dopamine D2 receptor agonists, respectively. Dopamine-stimulated activity was inhibited by several dopamine receptor antagonists with the following rank order of potency: (+)-butaclamol > spiperone > raclopride > S(-)-sulpiride; but not by (-)-butaclamol or SCH 23390. High-affinity GTPase activity was also stimulated by carbachol and acetylcholine through the pirenzepine-insensitive muscarinic receptors. Preincubation of the membranes with AS/7, a specific antiserum to Gi1 and Gi2, appeared to attenuate dopamine-sensitive activity, suggesting that Gi1 and/or Gi2 may be at least partially involved. These results indicate that high-affinity GTPase activity in rat striatal membranes is activated through dopamine D2-like receptors and pirenzepine-insensitive muscarinic receptors, both of which are negatively coupled to adenylate cyclase via Gi proteins.
Odagaki
Y
Y
Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
Fuxe
K
K
D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015636:Magnesium Chloride / Q000494:pharmacology; D008297:Male; D018721:Muscarinic Agonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D018721:Muscarinic Agonists; D017448:Receptors, Dopamine D2; D011976:Receptors, Muscarinic; D015636:Magnesium Chloride; D012965:Sodium Chloride; D002217:Carbachol; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D004298:Dopamine