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Dibutyryl‐cAMP (dbcAMP) up‐regulates astrocytic chloride‐dependent l ‐[ 3 H]glutamate transport and expression of both system x c − subunits
Author(s) -
Gochenauer Gordon E.,
Robinson Michael B.
Publication year - 2001
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2001.00385.x
Subject(s) - glutamate receptor , chemistry , transporter , dids , metabotropic glutamate receptor , biophysics , forskolin , biochemistry , biology , receptor , membrane , gene
Recent studies have shown that N 6 ,2′‐ O ‐dibutyryladenosine 3′:5′ cyclic monophosphate (dbcAMP) increases the expression of specific subtypes of Na + ‐dependent glutamate transporters in cultured astrocytes. Our group also found that treatment of astrocytes with dbcAMP for several days increases the Na + ‐independent accumulation of l ‐[ 3 H]glutamate. In this study, the properties of this Na + ‐independent accumulation were characterized, and the mechanism by which dbcAMP up‐regulates this process was investigated. This accumulation was markedly reduced in the absence of Cl − and was also inhibited by several anion‐exchange inhibitors, including 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid, 4,4′‐dinitrostilbene‐2,2′‐disulfonic acid and 4‐acetamido‐4′‐isothiocyanatostilbene‐2,2′‐disulfonic acid, suggesting that this activity is mediated by a Cl − ‐dependent transporter. In addition, this activity was inhibited by micromolar concentrations of several inhibitors of another Cl − ‐dependent (Na + ‐independent) transport activity frequently referred to as system x c − ( l ‐cystine, l ‐α‐aminoadipate, l ‐homocysteate, quisqualate, β‐ N ‐oxalyl‐l‐α,β‐diaminopropionate, ibotenate). This activity was competitively inhibited by several phenylglycine derivatives previously characterized as inhibitors of metabotropic glutamate receptor activation. The concentration‐dependence for Na + ‐independent, Cl − ‐dependent l ‐[ 3 H]glutamate uptake activity was compared for dbcAMP‐treated and untreated astrocytes. Treatment with dbcAMP increased the V max of this Cl − ‐dependent transport activity by sixfold but had no effect on the K m value. System x c − requires two subunits, xCT and 4F2hc/CD98, to reconstitute functional activity. We found that dbcAMP caused a twofold increase in the levels of xCT mRNA and a sevenfold increase in the levels of 4F2hc/CD98 protein. This study indicates that dbcAMP up‐regulates Cl − ‐dependent l ‐[ 3 H]glutamate transport activity in astrocytes and suggests that this effect is related to increased expression of both subunits of system x c − . Because this activity is thought to be important for the synthesis of glutathione and protection from oxidant injury, understanding the regulation of system x c − may provide alternate approaches to limit this form of injury.