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Glutamate-induced internalization of Ca(v)1.3 L-type Ca(2+) channels protects retinal neurons against excitotoxicity
Fengxia Mizuno1, Peter Barabas, David Krizaj
1Department of Ophthalmology, NYU Medical Center, New York, NY 10016, USA.
Abstract:
Glutamate-induced rise in the intracellular Ca(2+) level is thought to be a major cause of excitotoxic cell death, but the mechanisms that control the Ca(2+) overload are poorly understood. Using immunocytochemistry, electrophysiology and Ca(2+) imaging, we show that activation of ionotropic glutamate receptors induces a selective internalization of Ca(v)1.3 L-type Ca(2+) channels in salamander retinal neurons. The effect of glutamate on Ca(v)1.3 internalization was blocked in Ca(2+)-free external solution, or by strong buffering of internal Ca(2+) with BAPTA. Downregulation of L-type Ca(2+) channel activity in retinal ganglion cells by glutamate was suppressed by inhibitors of dynamin-dependent endocytosis. Stabilization of F-actin by jasplakinolide significantly reduced the ability of glutamate to induce internalization suggesting it is mediated by Ca(2+)-dependent reorganization of actin cytoskeleton. We showed that the Ca(v)1.3 is the primary L-type Ca(2+) channel contributing to kainate-induced excitotoxic death of amacrine and ganglion cells. Block of Ca(v)1.3 internalization by either dynamin inhibition or F-actin stabilization increased vulnerability of retinal amacrine and ganglion cells to kainate-induced excitotoxicity. Our data show for the first time that Ca(v)1.3 L-type Ca(2+) channels are subject to rapid glutamate-induced internalization, which may serve as a negative feedback mechanism protecting retinal neurons against glutamate-induced excitotoxicity.
Insights
Glutamate receptor activation triggers the internalization of L-type calcium channels (Ca(v)1.3) in retinal neurons. This process protects against excitotoxic cell death by regulating calcium overload.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- Glutamate excitotoxicity is a significant cause of neuronal cell death, particularly in the retina.
- The precise mechanisms controlling calcium (Ca2+) overload during excitotoxicity remain incompletely understood.
- L-type calcium channels are implicated in neuronal function and vulnerability.
Purpose of the Study:
- To investigate the mechanisms underlying glutamate-induced calcium overload in retinal neurons.
- To determine the role of L-type calcium channels in excitotoxic cell death.
- To elucidate the regulation of Ca(v)1.3 L-type calcium channels by glutamate.
Main Methods:
- Immunocytochemistry, electrophysiology, and Ca2+ imaging were employed.
- Experiments utilized salamander retinal neurons, including retinal ganglion cells and amacrine cells.
- Pharmacological agents targeting endocytosis (dynamin inhibitors) and actin cytoskeleton (jasplakinolide) were used.
Main Results:
- Activation of ionotropic glutamate receptors induced selective internalization of Ca(v)1.3 L-type Ca2+ channels.
- This internalization was dependent on extracellular Ca2+, internal Ca2+ buffering, dynamin-dependent endocytosis, and actin cytoskeleton reorganization.
- Ca(v)1.3 channels were identified as the primary contributors to kainate-induced excitotoxicity in retinal neurons; blocking their internalization exacerbated cell death.
Conclusions:
- Ca(v)1.3 L-type Ca2+ channels undergo rapid, glutamate-induced internalization in retinal neurons.
- This internalization acts as a protective negative feedback mechanism against glutamate-induced excitotoxicity.
- Understanding this process offers potential therapeutic targets for retinal neurodegenerative diseases.
