Related Experiment Videos
Ca2+ influx through glutamate receptor-associated channels in retina cells correlates with neuronal cell death
I L Ferreira1, C B Duarte, A P Carvalho
1Center for Neurosciences of Coimbra, Department of Zoology, University of Coimbra, Portugal.
Abstract:
We studied the effect of glutamate, N-methyl-D-aspartate (NMDA), kainate or K+ depolarization, on neurotoxicity in cultured chick retinal cells, under conditions in which we could discriminate between Ca2+ entering through ionotropic glutamate receptors and voltage-sensitive Ca2+ channels (VSCCs). When neurons were challenged with NMDA, kainate or glutamate, in Na(+)-containing medium, a decrease in cell survival was observed, whereas K+ depolarization did not affect the viability of the cells. The Mg2+ ion completely prevented the toxic effect mediated by the NMDA receptor, and had a small but significant protective effect at the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate (AMPA/kainate) receptor-induced cell death. We observed that, in a Na(+)-free N-methyl-D-glucamine (NMG) medium, to avoid the activation of VSCCs indirectly by the glutamate receptor agonists, stimulation of the glutamate receptors causes Ca2+ influx only through NMDA and AMPA/kainate receptor-associated channels, and that Ca2+ entry correlates well with subsequent cell death. These results show that the activation of NMDA or AMPA/kainate receptors can cause excitotoxicity in retinal neurons by mechanisms not involving Na+ influx, but rather depending on the permeation of Ca2+ through glutamate receptor-associated channels. For small Ca2+ loads the entry of Ca2+ through the NMDA receptor-associated channel was more efficient in triggering cell death than the influx of Ca2+ through the AMPA/kainate receptor.
Insights
Glutamate receptor activation causes excitotoxicity in retinal neurons. Calcium influx through NMDA and AMPA/kainate receptors, not sodium, drives this neurotoxicity, with NMDA receptors being more potent.
Area of Science:
- Neuroscience
- Cell Biology
- Neuropharmacology
Background:
- Excitotoxicity is a major mechanism of neuronal damage.
- Ionotropic glutamate receptors play a critical role in synaptic transmission and neuronal survival.
- Distinguishing calcium influx pathways is crucial for understanding excitotoxicity.
Purpose of the Study:
- To investigate the role of calcium (Ca2+) influx through ionotropic glutamate receptors versus voltage-sensitive Ca2+ channels (VSCCs) in excitotoxicity of cultured chick retinal cells.
- To differentiate the neurotoxic effects mediated by N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate (AMPA/kainate) receptors.
Main Methods:
- Cultured chick retinal cells were exposed to glutamate, NMDA, kainate, or K+ depolarization.
- Experiments were conducted in both Na(+)-containing and Na(+)-free (NMG) media to isolate receptor-mediated Ca2+ influx.
- Cell survival was assessed following receptor stimulation.
Main Results:
- NMDA, kainate, or glutamate exposure decreased cell survival in Na(+)-containing medium, while K+ depolarization did not.
- Magnesium (Mg2+) ions blocked NMDA receptor-mediated toxicity and partially protected against AMPA/kainate receptor-induced cell death.
- In Na(+)-free medium, glutamate receptor stimulation led to Ca2+ influx solely through NMDA and AMPA/kainate receptor channels, correlating with cell death.
Conclusions:
- Activation of NMDA and AMPA/kainate receptors induces excitotoxicity in retinal neurons primarily through Ca2+ permeation via these receptors, independent of Na+ influx.
- The NMDA receptor channel is more efficient than the AMPA/kainate receptor channel at triggering cell death with small Ca2+ loads.