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System xc‐ is an electrogenic cystine/glutamate exchanger
Author(s) -
Sierzant Charles G.,
Lewis Brietney,
Chase Leah A.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a244-d
Subject(s) - cystine , glutamate receptor , chemistry , extracellular , xenopus , chloride , biophysics , biochemistry , biology , organic chemistry , enzyme , receptor , cysteine , gene
System x c − is a chloride‐dependent, cystine/glutamate exchanger which is expressed in many cell types including neurons, glia, fibroblasts and macrophages. Previous studies in our lab have demonstrated that chloride increases the affinity of cystine for the transport system. However, it is not currently known whether System ‐ x ‐c − ‐mediated cystine/glutamate exchange requires the net influx of chloride into the cell. Using a Xenopus oocyte expression system and a two‐electrode voltage clamp, we sought to determine if chloride transport was thermodynamically coupled to cystine/glutamate exchange. Here we report that System x c − ‐mediated currents were observed upon exposure to cystine in a dose dependent manner. Furthermore, these currents exhibit a K m of 40 μM for cystine which is similar to the previous reported value obtained from radioactive uptake assays. Finally, we report that the observed current is insensitive to changes in extracellular chloride. Specifically, we observed that there was no variation in the reversal potential of the observed currents. These data demonstrate that system x c − is electrogenic and suggest that cystine/glutamate exchange may not be thermodynamically coupled to chloride transport.