Duration 5min, Q&A 3min
Pressure-Dependent Changes of Glutamate Transporters in the Ex Vivo Rat Retinal Preparation
Excitotoxicity is thought to contribute to the pathogenesis of glaucoma. Mueller glia maintains an intimate relationship with retinal neurons and plays a crucial role in regulating extracellular glutamate levels. Glutamate is transported into Mueller glia via glutamate transporters (GLAST and GLT1) and is catalyzed by glutamine synthetase (GS) to the nontoxic amino acid glutamine. In the present study, we examined changes in GLAST and GLT1 splice variants expression and their functions in ex vivo rat retinas exposed to acute increases in ambient pressure.
All experiments were performed in accordance with the guidelines of the ARVO animal statement. Rat ex vivo specimens were prepared from approximately 30 day old male Sprague Dawley rats (Charles River Laboratories International Inc).
Retinal preparations were exposed to elevated hydrostatic pressure (75 mmHg) for 24 hours. To determine whether changes in transporter function mimic the effects of increased pressure, we used TFB-TBOA, a broad spectrum inhibitor glutamate transporters, and WAY213613, a specific inhibitor of GLT1. The expression of major glutamate transporter, GLAST and glutamine synthetase (GS) was examined by real-time PCR analysis. Splice variants of GLT1 were also examined.
Results and Conclusion
In this acute glaucoma model, we found that the characteristic axonal swelling in the nerve fiber layer induced by elevated pressure (75 mmHg) was mimicked by administration of 20 nM TFB-TBOA. By contrast, administration of WAY213613 did not show any changes in the retina. Real-time RT-PCR revealed a significant decrease in the expression of GLAST, suggesting that glial glutamate transport is impaired in the presence of increased IOP. By contrast, there were no remarkable changes in GLT-1 splice variant expression. We conclude that the retina is at the risk during IOP elevation because of impairment in glutamate transporters, mainly GLAST.
[ Keyword ]
glaucoma / glutamate transporter / pressure
[ Conflict of Interest ]