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Diabetes 53:2110-2116, 2004
© 2004 by the American Diabetes Association, Inc.

Oxidative Stress Affects Synaptosomal {gamma}-Aminobutyric Acid and Glutamate Transport in Diabetic Rats

The Role of Insulin

Ana I. Duarte1,2, Maria S. Santos1,2, Raquel Seiça1,3, and Catarina R. Oliveira1,4

1 Center for Neuroscience of Coimbra, University of Coimbra, Coimbra, Portugal
2 Department of Zoology, Faculty of Sciences and Technology, University of Coimbra, Coimbra, Portugal
3 Institute of Physiology, Faculty of Medicine, University of Coimbra, Coimbra, Portugal
4 Institute of Biochemistry, Faculty of Medicine, University of Coimbra, Coimbra, Portugal

Evidence suggests that oxidative stress is involved in the pathophysiology of diabetic complications and that insulin has a neuroprotective role in oxidative stress conditions. In this study, we evaluated the in vitro effect of insulin in the susceptibility to oxidative stress and in the transport of the amino acid neurotransmitters {gamma}-aminobutyric acid (GABA) and glutamate in a synaptosomal fraction isolated from male type 2 diabetic Goto-Kakizaki (GK) rat brain cortex. The ascorbate/Fe2+-induced increase in thiobarbituric acid reactive substances (TBARSs) was similar in Wistar and GK rats and was not reverted by insulin (1 µmol/l), suggesting that other mechanisms, rather than a direct effect in membrane lipid peroxidation, may mediate insulin neuroprotection. Diabetes did not affect GABA and glutamate transport, despite the significant decrease in membrane potential and ATP/ADP ratio, and insulin increased the uptake of both GABA and glutamate in GK rats. Upon oxidation, there was a decrease in the uptake of both neurotransmitters and an increase in extrasynaptosomal glutamate levels and in ATP/ADP ratio in GK rats. Insulin treatment reverted the ascorbate/Fe2+-induced decrease in GABA accumulation, with a decrease in extrasynaptosomal GABA. These results suggest that insulin modulates synaptosomal GABA and/or glutamate transport, thus having a neuroprotective role under oxidizing and/or diabetic conditions.

Address correspondence and reprint requests to Prof. Catarina Resende de Oliveira, Center for Neuroscience of Coimbra Institute of Biochemistry, Faculty of Medicine, University of Coimbra, 3004-517 Coimbra, Portugal. E-mail: catarina{at}cnc.cj.uc.pt


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Copyright © 2004 by the American Diabetes Association.