Pharmacological characterization of metabotropic glutamate receptor-mediated high-affinity GTPase activity in rat cerebral cortical membranes.
Activation of heterotrimeric guanine nucleotide-binding regulatory proteins (G-proteins) functionally coupled to metabotropic glutamate receptors (mGluRs) was assessed by agonist-induced high-affinity GTPase (EC3.6.1.-) activity in rat cerebral cortical membranes. L-Glutamate (1 mM) stimulated high-affinity GTPase activity to the same extent throughout the incubation period up to 20 min, in a Mg(2+)-dependent manner. The addition of 1 mM L-glutamate augmented V(max) of the enzyme activity (1670 to 3850 pmol mg(-1) protein 15 min(-1)) with slight increase in K(M) value (0.26 to 0.63 microM). The high-affinity GTPase activity was stimulated by the following compounds with a rank order of potency of (2S,2'R,3'R)-2-(2', 3'-dicarboxycyclopropyl) glycine (DCG-IV) > (2S,1'S, 2'S)-2-(carboxycyclopyropyl)glycine (L-CCG-I) > L-glutamate > or = 2R, 4R-4-aminopyrrolidine-2,4-dicarboxylate [(2R,4R)-APDC] > 1S, 3R-1-aminocyclopentane-1,3-dicarboxylate [(1S,3R)-ACPD] > (S)-4-carboxy-3-hydroxyphenylglycine [(S)-4C3HPG] > (S)-3-carboxy-4-hydroxyphenylglycine [(S)-3C4HPG] > ibotenate, but not by L-(+)-2-amino-4-phosphonobutyrate (L-AP4), (RS)-3, 5-dihydroxyphenylglycine [(RS)-3,5-DHPG], quisqualate, or L-serine-O-phosphate (L-SOP), indicative of involvement of group II mGluRs, in particular mGluR2. (2S)-alpha-Ethylglutamate (EGLU), a presumably selective antagonist against group II mGluRs, inhibited DCG-IV-stimulated high-affinity GTPase activity in a competitive manner with an apparent K(B) of 220 microM. L-Glutamate-stimulated activity was eliminated by pretreatment of the membranes with sulfhydryl alkylating agent N-ethylmaleimide (NEM) at 30-50 microM, indicating that G-proteins of the G(i) family are involved. These results indicate that mGluR agonist-induced high-affinity GTPase activity in rat cerebral cortical membranes may be used to detect the functional interaction between group II mGluRs, in particular mGluR2, and NEM-sensitive G(i) proteins.
Nishi
N
N
Department of Psychiatry, Hokkaido University School of Medicine, North 15, West 7, Sapporo 060-8638, Japan.
Odagaki
Y
Y
Koyama
T
T
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism*
D004791:Enzyme Inhibitors; D018690:Excitatory Amino Acid Agonists; D017470:Receptors, Glutamate; D018698:Glutamic Acid; D020558:GTP Phosphohydrolases; D005033:Ethylmaleimide