Year of Award


Document Type


Degree Type

Doctor of Philosophy (PhD)

Department or School/College

Department of Biomedical and Pharmaceutical Sciences

Committee Chair

Richard J. Bridges

Commitee Members

Barrell Jackson, Fernando Cardozo-Paelez, Jean Pfau, Michele McGuirl


Camp, glia, thiols, transport


University of Montana


The system xC- (SxC-) transporter functions under normal physiological conditions in astrocytes to mediate the exchange of extracellular cystine (L-Cys2) for intracellular glutamate (L-Glu). The internalized L-Cys2 serves as a rate-limiting precursor in the biosynthesis of glutathione (GSH), while the externalized L-Glu can access EAA receptors and contribute to either excitatory signaling or excitotoxcity. Although the regulation of SxC- has been studied in a variety of cells, particularly as related to xenobiotic exposure, much less is known about its regulation in astrocytes. In the present study the influence of phenotype (culturing in the presence of dibutyryl-cAMP) and GSH levels on the expression of SxC- was investigated in cultures of primary astrocytes prepared from neonatal rats. We report that SxC- activity in the dbcAMP-treated cells was nearly 7-fold greater than in untreated astrocytes (100 ± 21 and 15 ± 4 pmol/min/mg protein respectively) and that this uptake was further upregulated (~3-fold) in these cells following the depletion of intracellular GSH levels with buthionine sulfoximine (BSO, 500 μM, 24 hrs). Changes in SxC- activity correlated with: increases in both protein and mRNA levels of the xCT subunit of the SxC- heterodimer, an increase in the Vmax for SxC---mediated L-Glu uptake (147 ± 5 in untreated astrocytes to 350 ± 15 pmol/min/mg protein in dbcAMP-treated), and was linked temporally to alterations in GSH levels. The GSH depletion-induced induction of SxC- was not mimicked by tBHQ or non-specific oxidants and was partially preventable by the co-administration of cell permeant thiols GSH-ethyl ester (5 mM) and N-acetylcysteine (NAC). These findings demonstrate that the expression of SxC- on astrocytes is dynamically regulated by intracellular GSH levels in a cell- and phenotype-dependent manner. The presence of this pathway likely reflects the inherent vulnerability of the CNS to oxidative damage and raises interesting questions as to the functional consequences of changes in SxC- activity in CNS injury and disease.



© Copyright 2010 Todd Seib