Protection from oxidant injury by sodium-dependent GSH uptake in retinal Muller cells

Glutathione (GSH) is known to play an important role in regulating oxidative damage to cells. The present study was initiated to examine the effect of exogenous GSH on oxidative injury in a retinal Muller cell line and to characterize GSH transport in these cells. Rat Muller cells (rMC-1) were incubated with varying concentrations of t-butylhydroperoxide (t-BHP) to induce oxidative stress, and cell viability was measured after addition of GSH. In other studies, kinetics of GSH uptake and Na⁺-dependency were examined by incubating cells with ³⁵S-GSH in Na⁺-containing and Na⁺-free buffers. GSH uptake was studied with GSH at concentrations varying from 0·05-10 mM in NaCl buffer. In the presence of sodium, extracellular GSH provided protection against t-BHP-induced oxidant injury to rMC-1 cells; in contrast, the amino acid precursors of GSH did not have any effect on cell viability. GSH was taken up by rMC-1 cells in a concentration- and sodium- dependent manner. Kinetic studies revealed both a high affinity (K(m) 0·31 mm) and low affinity K(m) (~ 4·2 mm) component. Furthermore, GSH depletion had no significant effect on the rate of GSH uptake. The results show that physiological concentrations of GSH can protect Muller cells from oxidative injury. Both Na⁺-dependent and Na⁺-independent transport systems for GSH exist in Muller cells, and the Na⁺-dependent GSH transporter may be involved in the protective role of GSH.