Prolonged inhibition of glutamate reuptake down-regulates NMDA receptor functions in cultured cerebellar granule cells.
In the present study, we have examined the effects of prolonged (up to 72 h) inhibition of high-affinity glutamate reuptake by L-trans-pyrrolidine-2,4-dicarboxylate (PDC; 100 microM) on glutamate receptor functions in primary cultures of rat cerebellar granule neurons. This was done by comparing the effects of various glutamate receptor agonists on neuronal 45Ca2+ uptake, free cytoplasmic Ca2+ concentration ([Ca2+]i), and cell viability. We also determined the parameters of[3H]MK-801 binding as well as the expression of the NMDAR1 subunit protein in control and PDC-exposed cultures. The blockade of glutamate reuptake by PDC led to a gradual increase of ambient glutamate to concentrations that are neurotoxic when applied acutely to control cells. In PDC-exposed cells, however, the acute glutamate-induced NMDA receptor-mediated calcium fluxes were strongly diminished and no toxicity was observed. The down-regulation of the functional effects of glutamate was dependent on the duration of PDC exposure and was accompanied by a reduced NMDAR1 subunit expression and decreased [3H]MK-801 binding, indicative of a pronounced structural rearrangement of NMDA receptors. The possibility that the decrease of NMDA glutamate receptor sensitivity can be explained on the basis of a reduced density or altered subunit composition of NMDA receptors is discussed.
Cebers
G
G
Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Cebere
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A
Wägner
A
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Liljequist
S
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D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D053938:DNA Fragmentation; D003998:Dicarboxylic Acids / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates / Q000378:metabolism; D006657:Histones / Q000235:genetics; D009474:Neurons / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013997:Time Factors
D003998:Dicarboxylic Acids; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D006657:Histones; D009498:Neurotoxins; D014179:Neurotransmitter Uptake Inhibitors; D011759:Pyrrolidines; D016194:Receptors, N-Methyl-D-Aspartate; D016291:Dizocilpine Maleate; C083486:pyrrolidine-2,4-dicarboxylic acid; D002118:Calcium