Reducing conditions differentially affect the functional and structural properties of group-I and -II metabotropic glutamate receptors

A. Copani, C. Romano, V. Di Giorgi Gerevini, A. Nicosia, G. Casabona, M. Storto, V. Mutel, F. Nicoletti

Research output: Contribution to journalArticle

Abstract

We have examined the influence of reducing conditions on the activity of group-I or -II metabotropic glutamate receptors. In cultured cerebellar granule cells or in hippocampal slices, the reducing agent dithiothreitol (DTT) inhibited the stimulation of polyphosphoinositide (PPI) hydrolysis elicited by group-I mGlu receptor agonists without affecting responses to norepinephrine or carbamylcholine. Similarly, DTT reduced the increase in intracellular free Ca2+ induced by glutamate in HEK-293 cells expressing mGlu5 receptors. In adult hippocampal slices, the selective group-II mGlu receptor agonist, (2S,1'R,2'R,3'R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG- IV) had no effect per se on PPI hydrolysis, but potentiated the response to quisqualate. Although DTT substantially attenuated the action of quisqualate, it did not affect the potentiation by DCG-IV, suggesting that group-II mGlu receptors are resistant to extracellular reduction. Accordingly, DTT did not affect the inhibition of forskolin-stimulated cAMP formation induced by maximally effective concentrations of group-II mGlu receptor agonists in hippocampal slices or in CHO cells expressing mGlu2 receptors. At structural level, DTT differentially affected the aggregation state of mGlu1a, -2/3 or - 5 receptors. In immunoblots performed under non-reducing conditions, mGlu1a, -2/3 or -5 antibodies labeled exclusively a high-molecular weight band, corresponding to receptor dimers. Under reducing conditions, mGlu1a or -5 receptors were detected as monomers, whereas a large proportion of mGlu2/3 receptors was still present in a dimeric form. We conclude that reducing conditions differentially influence the aggregation state of group-I and -II mGlu receptors and suggest that dimerization affects the functional activity of native mGlu receptors. (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)165-172
Number of pages8
JournalBrain Research
Volume867
Issue number1-2
DOIs
Publication statusPublished - Jun 9 2000

Keywords

  • Dimerization
  • Metabotropic glutamate receptor
  • Signal transduction

ASJC Scopus subject areas

  • Neuroscience(all)

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