These authors contributed equally to this work.
Hypo-osmotic swelling modifies glutamate-glutamine cycle in the cerebral cortex and in astrocyte cultures
Article first published online: 19 MAY 2011
© 2011 The Authors. Journal of Neurochemistry © 2011 International Society for Neurochemistry
Journal of Neurochemistry
Volume 118, Issue 1, pages 140–152, July 2011
How to Cite
Hyzinski-García, M. C., Vincent, M. Y., Haskew-Layton, R. E., Dohare, P., Keller, Jr., R. W. and Mongin, A. A. (2011), Hypo-osmotic swelling modifies glutamate-glutamine cycle in the cerebral cortex and in astrocyte cultures. Journal of Neurochemistry, 118: 140–152. doi: 10.1111/j.1471-4159.2011.07289.x
- Issue published online: 10 JUN 2011
- Article first published online: 19 MAY 2011
- Accepted manuscript online: 23 APR 2011 12:25AM EST
- Received November 30, 2010; revised manuscript April 1, 2011; accepted April 19, 2011.
- cell swelling;
- glutamate-glutamine cycle;
- glutamine synthetase;
J. Neurochem. (2011) 10.1111/j.1471-4159.2011.07289.x
In our previous work, we found that perfusion of the rat cerebral cortex with hypo-osmotic medium triggers massive release of the excitatory amino acid L-glutamate but decreases extracellular levels of L-glutamine (R. E. Haskew-Layton et al., PLoS ONE, 3: e3543). The release of glutamate was linked to activation of volume-regulated anion channels, whereas mechanism(s) responsible for alterations in extracellular glutamine remained unclear. When mannitol was added to the hypo-osmotic medium to reverse reductions in osmolarity, changes in microdialysate levels of glutamine were prevented, indicating an involvement of cellular swelling. As the main source of brain glutamine is astrocytic synthesis and export, we explored the impact of hypo-osmotic medium on glutamine synthesis and transport in rat primary astrocyte cultures. In astrocytes, a 40% reduction in medium osmolarity moderately stimulated the release of L-[3H]glutamine by ∼twofold and produced no changes in L-[3H]glutamine uptake. In comparison, hypo-osmotic medium stimulated the release of glutamate (traced with D-[3H]aspartate) by more than 20-fold. In whole-cell enzymatic assays, we discovered that hypo-osmotic medium caused a 20% inhibition of astrocytic conversion of L-[3H]glutamate into L-[3H]glutamine by glutamine synthetase. Using an HPLC assay, we further found a 35% reduction in intracellular levels of endogenous glutamine. Overall, our findings suggest that cellular swelling (i) inhibits astrocytic glutamine synthetase activity, and (ii) reduces substrate availability for this enzyme because of the activation of volume-regulated anion channels. These combined effects likely lead to reductions in astrocytic glutamine export in vivo and may partially explain occurrence of hyperexcitability and seizures in human hyponatremia.