Characterization of cystine uptake in cultured astrocytes

Glutathione is involved in the maintenance of the structural and functional integrity of membrane proteins, in protection against free radicals and ox idative stress, and in the detoxification of xenobiotics. The cellular upta ke of cystine is the rate limiting step in the biosynthesis of glutathione. The precise mechanism for such uptake is not clear as some reports indicat e that the uptake occurs through a glutamate-cystine antiporter (system X-c (-)), whereas, others suggest that it is taken up by the glutamate transpor ter (system X-AG) Our studies in cultured astrocytes derived from neonatal rats showed that glutamate, D- and L-aspartate inhibited cystine uptake; th at factors that increased intracellular glutamate levels, which would have enhanced the activity of the antiporter, did not stimulate cystine uptake; that the uptake was sodium dependent and partially chloride dependent; that the b(o,+) and ASC systems, which have been shown to carry cystine in some cells, did not mediate cystine uptake in astrocytes; that glutamate uptake blockers such as L-aspartate-beta-hydroxamate (A beta H) and L-trans-pyrro lidine-2,4-dicarboxylate (PDC), as well as cystine uptake inhibitor L-alpha -aminoadipate (AAA) potently reduced cystine uptake. Additionally, deferoxa mine (100 mu M) as well as ammonium chloride (5 mM), both of which inhibit glutamate uptake, also inhibited cystine uptake. Taken together, our findin gs indicate that astrocytes take up cystine through a similar, if not ident ical, system used to take up glutamate. Interference of cystine uptake by a strocytes through the glutamate transport system may have profound effects on the redox state and the structural and functional integrity of the CNS. Published by Elsevier Science Ltd.