INHIBITION OF GLUTAMATE TRANSPORT IN SYNAPTOSOMES BY DOPAMINE OXIDATION AND REACTIVE OXYGEN SPECIES

Dopamine can form reactive oxygen species and other reactive metabolit es that can modify proteins and other cellular constituents. In this s tudy, we tested the effect of dopamine oxidation products, other gener ators of reactive oxygen species, and a sulfhydryl modifier on the fun ction of glutamate transporter proteins. We also compared any effects with those on the dopamine transporter, a protein whose function we ha d previously shown to be inhibited by dopamine oxidation, Preincubatio n with the generators of reactive oxygen species, ascorbate (0.85 mM) or xanthine (500 mu M) plus xanthine oxidase (25 mU/ml), inhibited the uptake of [H-3]glutamate (10 mu M) into rat striatal synaptosomes (-5 4 and -74%, respectively), The sulfhydryl-modifying agent N-ethylmalei mide (50-500 mu M) also led to a dose-dependent inhibition of [H-3]glu tamate uptake. Preincubation with dopamine (100 mu M) under oxidizing conditions inhibited [H-3]glutamate uptake by 25%. Exposure of synapto somes to increasing amounts of dopamine quinone by enzymatically oxidi zing dopamine with tyrosinase (2-50 U/ml) further inhibited [H-3]gluta mate uptake, an effect prevented by the addition of glutathione. The e ffects of free radical generators and dopamine oxidation on [H-3]-glut amate uptake were similar to the effects on [H-3]-dopamine uptake (250 nM). Our findings suggest that reactive oxygen species and dopamine o xidation products can modify glutamate transport function, which may h ave implications for neurodegenerative processes such as ischemia, met hamphetamine-induced toxicity, and Parkinson's disease.