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TB Redens, R Van Norman, MP Langford; Evaluation of Glutamate Transporter Activity in Human Cataractous Lenses . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4647.
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Purpose: We have previously reported the detection of Na+-dependent EAAT1 and EAAT2 glutamate (Glu) transporters (Xag system) in transformed human lens epithelial cells. The present study presents the Xag (Na+-dependent) and Xc (Na+-independent) Glu transport activities in phaco-emulsified human cataractous lens. Methods: Fifty phaco-emulsified human cataractous lenses were classified and evaluated for Na+-dependent and Na+-independent Glu transport activity. Results: D-Aspartate and threo-ß-hydroxyaspartate inhibited Xag uptake of Glu by EAAT1 while kainate inhibited EAAT2 transport in human cataractous lens. Cystine inhibited Na+-independent Xc transport of radiolabeled L-Glu in human cataractous lenses. The Xag transport of radiolabeled L-Glu by the human cataractous lens was 2-fold higher than by the Xc transport activity (p=.02). Interestingly, the Xag transport of radiolabeled D-aspartate by the human cataract lens was 4-10 fold less (p's<.05) than for radiolabeled L-Glu. While the amount and type of transport activity varied with regard to the cataract type, a statistical significant difference was not detected. However, [3H]-D-Asp uptake by non-insulin diabetic lens was significantly greater than by insulin-dependent diabetic lenses (p=.008; n=5). Conclusion: Our results indicate that the Glu transport by Na+-dependent and Na+-independent systems are detectable in phaco-emulsified human cataractous lens and suggest that type I diabetic lens may have reduced Glu transport activity.
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