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Glutamate regulates the viability of retinal cells in culture
A C Rego1, M S Santos, F Areias
1Center for Neurosciences of Coimbra and Laboratory of Biochemistry, Faculty of Medicine, University of Coimbra, 3004-504, Coimbra, Portugal.
Abstract:
In this study, we show that glutamate regulates the viability of cultured retinal cells upon transient glucose deprivation. At low concentrations (10-100 microM) glutamate decreased MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] reduction to about 50% of control and decreased intracellular ATP levels (about 4-fold) after transient glucose removal. Under these conditions, the decrease in MTT reduction was associated with the activation of NMDA (N-methyl-D-aspartate) receptors. Upon exposure to high (10 mM) glutamate and transient glucose deprivation, the intracellular levels of glutamate increased. High glutamate significantly counteracted the decrease in MTT reduction and ATP production observed in the presence of low glutamate concentrations. AOAA (aminooxyacetic acid), a non-specific inhibitor of mitochondrial transaminases, enhanced the intracellular glutamate levels, but did not largely affect glutamate-mediated changes in MTT reduction or ATP production. Furthermore, the intracellular levels of pyruvate were not significantly altered, suggesting that changes in ATP production were not due to an increase in glycolysis. Thus, the recovery from glucose deprivation seems to be facilitated in retinal neuronal cells that had been exposed to high glutamate, in comparison with low glutamate, suggesting a role for high glutamate and glucose in maintaining retinal cell function following conditions of glucose scarcity.
Insights
High glutamate levels protect cultured retinal cells from glucose deprivation by maintaining cell viability and ATP production, unlike low glutamate concentrations which impair these functions.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Glutamate is a key neurotransmitter in the retina.
- Retinal cells are vulnerable to metabolic stress, such as glucose deprivation.
- The role of glutamate concentration in retinal cell response to glucose scarcity is not fully understood.
Purpose of the Study:
- To investigate the effect of different glutamate concentrations on cultured retinal cell viability during transient glucose deprivation.
- To elucidate the mechanisms underlying glutamate's protective or detrimental effects on retinal cells under metabolic stress.
Main Methods:
- Cultured retinal cells were subjected to transient glucose deprivation.
- Cell viability was assessed using MTT reduction assays.
- Intracellular ATP levels were measured.
- N-methyl-D-aspartate (NMDA) receptor activation was monitored.
- Aminooxyacetic acid (AOAA) was used to inhibit mitochondrial transaminases.
Main Results:
- Low glutamate (10-100 microM) decreased MTT reduction and ATP levels, associated with NMDA receptor activation.
- High glutamate (10 mM) significantly counteracted these negative effects, preserving cell viability and ATP production.
- AOAA increased intracellular glutamate but did not significantly alter glutamate-mediated effects on cell viability or ATP.
- Pyruvate levels remained unchanged, indicating glycolysis was not the primary driver of ATP changes.
Conclusions:
- Glutamate concentration critically regulates retinal cell fate during glucose deprivation.
- High extracellular glutamate confers a protective effect, enhancing recovery and maintaining function under glucose scarcity.
- These findings suggest a potential therapeutic strategy involving glutamate modulation for retinal protection against ischemic injury.