Visualising the activity of the cystine-glutamate antiporter in glial cells using antibodies to aminoadipic acid, a selectively transported substrate

The cystine-glutamate antiporter is a transport system that facilitates the uptake of cystine, concomitant with the release of glutamate. The cystine accumulated by this transporter is generally considered for use in the form ation of the cysteine-containing antioxidant glutathione, which is abundant in many glial cells. This study used the simple strategy of generating an antibody to aminoadipic acid, a selective substrate for the cystine-glutama te antiporter. Stereospecific accumulation of aminoadipic acid into specifi c cell types in rat brain slice preparations was detected immunocytochemica lly. Strong accumulation was detected in astroglial cells in all brain regi ons studied including those in white matter tracts. Strong accumulation int o radial glial cells, including the retinal Muller cells and the Bergmann g lial cells was also observed. Glial accumulation was observed not only in c ells within the blood brain barrier, but also outside such; anterior pituit ary folliculostellate cell and intermediate lobe pituitary glial cells exhi bited strong accumulation of aminoadipic acid. Interestingly, some glial ce lls such as the posterior pituitary glial cells (pituicytes) exhibited very little if any accumulation of aminoadipic acid. Within the brain labelling was not uniform. Particularly strong labelling was noted in some regions, such as the glial cells surrounding the CA1 pyramidal cells. By contrast, n eurons never exhibited uptake of aminoadipic acid. Because cystine uptake i s associated with glutamate release, it is suggested that this antiporter m ight contribute to release of glutamate from glial cells under some pathoph ysiological conditions. (C) 2001 Wiley-Liss, Inc.