Cloning and Expression of Rat Metabotropic Glutamate Receptor 8 Reveals a Distinct Pharmacological Profile
- Julie A. Saugstad1,1,
- J. Mark Kinzie1,
- Michi M. Shinohara1,
- Thomas P. Segerson2 and
- Gary L. Westbrook1,3
- 1Vollum Institute for Advanced Biomedical Research (J.A.S., J.M.K., M.M.S., G.L.W.) and Departments of 2Medicine (T.P.S.) and 3Neurology (G.L.W.), Oregon Health Sciences University, Portland, Oregon 97201
Abstract
The metabotropic glutamate receptor (mGluR) cDNAs were originally cloned from rat, except for the mouse cDNA clone encoding mGluR8. Mouse mGluR8 couples weakly to the inhibition of adenylate cyclase, thus hindering the characterization of its pharmacological properties. We isolated a rat mGluR8 cDNA that encodes a protein of 908 amino acids.In situ hybridization revealed prominent mGluR8 mRNA expression in olfactory bulb, pontine gray, lateral reticular nucleus of the thalamus, and piriform cortex. Less abundant expression was detected in cerebral cortex, hippocampus, cerebellum, and mammillary body. Glutamate evoked pertussis toxin-sensitive potassium currents inXenopus laevis oocytes coexpressing mGluR8 and G protein-coupled inwardly rectifying potassium channels. mGluR8 was also activated by the group III-specific agonistl-2-amino-4-phosphonobutyric acid; (2(S),1′(S),2′(S)]-2-(carboxycyclopropyl)glycine, which has been frequently used as a selective group II agonist; and the nonselective agonist (1(S),3(R)]-1-aminocyclopentane-1,3-dicarboxylic acid but not by the group I-specific agonist 3,5-dihydroxyphenylglycine or the group II-specific agonist [2(S),1′(R),2′(R),3′(R)]-2-(2,3-dicarboxycyclopropyl)glycine. The agonist profile in order of potency was [2(S),1′(S),2′(S)]-2-(carboxycyclopropyl)glycine ≈ l-2-amino-4-phosphonobutyric acid > glutamate ≫ [1(S),3(R)]-1-aminocyclopentane-1,3-dicarboxylic acid, with EC50 values of 0.63, 0.67, 2.5, and 47 μm, respectively. Both the group I/II-specific antagonist (R,S)-α-methyl-4-carboxyphenylglycine and the group III-specific antagonist α-methyl-amino-phosphonobutyrate inhibited mGluR8. The pharmacological profile of mGluR8 is distinct among mGluRs but closely matches that of presynaptic inhibition in some central nervous system pathways. Thus, cellular responses mediated by both group II and III agonists may in some cases reflect activation of mGluR8 rather than multiple mGluR subtypes.
Footnotes
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Send reprint requests to: Dr. Gary L. Westbrook, Vollum Institute, L474, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201. E-mail: westbroo{at}ohsu.edu
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↵1 Current affiliation: Department of Pharmacology, Emory University Atlanta, GA 30322.
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↵3 J. M. Kinzie, M. M. Shinohara, A. van den Pol, G. L. Westbrook, and T. P. Segerson. Immunolocalization of metabotropic glutamate receptor 7 in the adult rat olfactory system, submitted for publication.
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This work was supported by National Institutes of Health Fellowships F32-NS09200 (J.A.S.), F30-MH10314 (J.M.K.), R01-DC01783 (T.P.S.), and R01-NS26494 (G.L.W.). We thank Weibin Zhang for harvesting the oocytes.
- Abbreviations:
- mGluR
- metabotropic glutamate receptor
- GIRK
- G protein-coupled inwardly rectifying potassium channel
- L-AP4
- l-2-amino-4-phosphonobutyric acid
- L-CCG-1
- [2(S),1′(S),2′(S)]-2-(carboxycyclopropyl)glycine
- ACPD
- [1(S),3(R)]-1-aminocyclopentane-1,3-dicarboxylic acid
- MCPG
- (R,S)-α-methyl-4-carboxyphenylglycine
- MAP4
- α-methyl-amino-phosphonobutyrate
- DCG-IV
- [2(S),1′(R),2′(R),3′(R)]-2-(2,3-dicarboxycyclopropyl)glycine
- DHPG
- 3,5-dihydroxyphenylglycine
- GABA
- γ-aminobutyric acid
- SSC
- standard saline citrate
- PTX
- pertussis toxin
- HEPES
- 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
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- Received July 31, 1996.
- Accepted September 25, 1996.
- The American Society for Pharmacology and Experimental Therapeutics
