Evaluation of Glutamate Transporter Activity in Human Cataractous Lenses

Abstract

Abstract: : 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.

Keywords: 338 cataract • 467 metabolism • 387 diabetes