Guanine based purines inhibit [(3)H]glutamate and [(3)H]AMPA binding at postsynaptic densities from cerebral cortex of rats.
Extracellular guanine-based purines (GBPs) have been implicated in neuroprotective effects against glutamate toxicity by modulating the glutamatergic system through mechanisms without the involvement of G proteins. Accordingly, GBPs have been shown to inhibit the binding of glutamate and its analogs in different brain membrane preparations. However, brain membrane preparations used for these studies are comprised of both post- and pre-neuronal and glial synaptic components. In this study we investigated the ability of GBPs to displaced glutamate and AMPA binding at postsynaptic densities (PSDs). PSDs are markedly prominent in glutamatergic synapses and retains the native apposition of membrane components and post synaptic receptors. The PSD fraction was prepared from cerebral cortex of Wistar rats and it was characterized as PSDs by electron microscopy and by an enrichment of PSD-95, a protein marker of PSDs (90% of immunodetection). Moreover, we detected an enrichment of glutamate receptors subunits that including NR1 subunit of NMDA receptors and GluR1 subunit of AMPA receptors. GppNp (poor hydrolyzable GTP analog) and GMP displaced 40 and 36% of glutamate binding, respectively, and guanosine only 23%. AMPA binding was not affected by guanosine and was inhibited 21 and 25% by GppNp and GMP, respectively. Hence, this study demonstrates that guanine based purines inhibited glutamate and AMPA binding at postsynaptic membrane preparations, contributing for a better understanding of the mechanisms by which GBPs antagonize glutamatergic neurotoxicicity, e.g. the possible involvement of glutamatergic postsynaptic receptors in their neuroprotective roles.
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Departamento de Bioquijmica, ICBS, UFRGS, Rua Ramiro Barcelos, 2600-Anexo, 90035-003 Porto Alegre/RS, Brazil.
Vinadé
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Wofchuk
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Souza
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D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects* / Q000502:physiology; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D000076122:Disks Large Homolog 4 Protein; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology*; D006147:Guanine / Q000378:metabolism*; D006157:Guanosine Monophosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D008854:Microscopy, Electron; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D018696:Neuroprotective Agents / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D018690:Excitatory Amino Acid Agonists; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018696:Neuroprotective Agents; D011687:Purines; D017470:Receptors, Glutamate; C033652:postsynaptic density proteins; D018698:Glutamic Acid; D006147:Guanine; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D006157:Guanosine Monophosphate; D006160:Guanosine Triphosphate