N-Methyl-D-aspartate receptor activation inhibits protein synthesis in cortical neurons independently of its ionic permeability properties.
Transient cerebral ischemia, which is accompanied by a sustained release of glutamate, strongly depresses protein synthesis. We have previously demonstrated in cortical neurons that a glutamate-induced increase in intracellular Ca(2+) is likely responsible for the blockade of the elongation step of protein synthesis. In this study, we provide evidence indicating that NMDA mobilizes a thapsigargin-sensitive pool of intracellular Ca(2+). Exposure of cortical neurons to NMDA, in the absence of external Ca(2+), produced a transient rise in intracellular Ca(2+) that was suppressed by pretreatment with thapsigargin. This rise in intracellular Ca(2+) did not result from an influx of Na(+) via reversal of the mitochondrial Na(+)/Ca(2+) exchanger since it persisted in a Na(+)-free medium or in the presence of CGP 37157, an inhibitor of the exchanger. Moreover, the NMDA-induced increase in intracellular Ca(2+) required the presence of D-serine, was blocked by D(-)-2-amino-5-phosphonopentanoic acid, but was not reduced in the presence of external Mg(2+). This unexpected non-ionotropic effect of NMDA was associated with an inhibition of protein synthesis that was also insensitive to the absence of external Ca(2+) or Na(+), or presence of Mg(2+). NMDA treatment resulted in an increase in the phosphorylation of eEF-2 in the absence or presence of external Ca(2+). The initiation step of protein synthesis was not blocked by NMDA since the phosphorylation of initiation factor eIF-2alpha subunit was not altered by NMDA treatment. In conclusion, we provide evidence indicating that NMDA can inhibit protein synthesis in cortical neurons through a process that involves the mobilization of intracellular Ca(2+) stores via a mechanism that is not linked to the ionic properties of NMDA receptors.
Gauchy
C
C
Laboratory of Neurobiology, INSERM U114, Collège de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France.
Nairn
A C
AC
Glowinski
J
J
Prémont
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D051379:Mice; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000502:physiology*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D015852:Eukaryotic Initiation Factor-2; D018690:Excitatory Amino Acid Agonists; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016202:N-Methylaspartate; D019284:Thapsigargin; D002118:Calcium