W. Reichelt et al., THE GLUTATHIONE LEVEL OF RETINAL MULLER GLIAL-CELLS IS DEPENDENT ON THE HIGH-AFFINITY SODIUM-DEPENDENT UPTAKE OF GLUTAMATE, Neuroscience, 77(4), 1997, pp. 1213-1224
The dependence of intracellular glutathione, an important radical scav
enger, on the extra cellular glutamate and cystine concentration and t
he velocity of the high affinity sodium/glutamate transporter was stud
ied in freshly-isolated Muller glial cells of the guinea-pig, kept in
vitro for up to 11 h. To this end the relative Muller cell glutathione
levels were measured using the fluorescent dye monochlorobimane, usin
g different concentrations of glutamate and cystine in Ringer solution
. In some experiments L-buthionine-[S,R]-sulfoximine, a blocker of glu
tathione synthesis, or L-trans-pyrrolidine-2,4-dicarboxylic acid and L
-alpha-aminoadipic acid, inhibitors of glutamate uptake, were added. T
he Muller cells maintained about 80% of the normal glutathione level w
hen maintained in Ringer solution containing 100 mu M glutamate for 11
h. When under these conditions 100 mu M cystine was added, the glutat
hione level increased to values, which were even higher than those at
the beginning of the incubation period. Addition of cystine without gl
utamate caused a run down of the glutathione level to about 45% of the
normal level, which is comparable to the run down in pure Ringer solu
tion. Likewise, application of L-buthionine[S,R]-sulfoximine (5 mM) le
ad to a strong run down of the glutathione level even in glutamate/cys
tine (100 mu M)-containing solution. A similar suppressing effect was
observed using L-trans-pyrrolidine-2,4-dicarboxylic acid and L-alpha-a
minoadipic acid in the presence of 100 mu M cystine and glutamate. We
conclude that the intracellular glutamate concentration of the Muller
cells is determined by the extracellular glutamate concentration and t
he velocity of the sodium/glutamate uptake. Consequently, cystine upta
ke into Muller cells, which is performed by the cystine/glutamate anti
porter, is fuelled by the sodium/glutamate transporter with intracellu
lar glutamate. Both glutamate and cystine are also substrates for glut
athione synthesis. The glutathione level is logically limited by the c
apacity of the sodium/glutamate transporter to provide glutamate intra
cellularly for, first, cystine uptake and, second, direct insertion in
to glutathione. Accordingly, the glutathione level is reduced when the
sodium/glutamate transporter is blocked. Thus, a diminution of the gl
utathione level should be taken into consideration when the effects of
sodium/glutamate uptake failure and reduced intracellular glutamate c
oncentrations are discussed. (C) 1997 IBRO. Published by Elsevier Scie
nce Ltd.