Glutathione oxidation in retina: effects on biochemical and electrical activities

This study investigates the possible role of glutathione (GSH) in defending the retina against oxidative damage. Freshly excised rat retina was found to contain 1.2 mumol/g wet wt GSH and an undetectable level of oxidized glutathione (GSSG). Whole retinas were either incubated or superfused with various concentrations of the GSH-oxidant diamide in order to study the effects of oxidation of GSH on the activity of the hexose monophosphate shunt (HMS) and on the receptor potential of the retina. It was found that exposure of the retina to diamide produced a stimulation of HMS activity up to 26-times that of the control. Significant changes in GSH content and receptor potential were observed at concentrations of diamide that produced more than a 5.4-fold stimulation of HMS activity. The diamide-induced electrical alterations included an increase in latency and peak time of the receptor potential, a delay in the onset of the off response and an increase in the time required for the potential to return to the baseline. It was found that nearly 80% of GHS could be regenerated and that most of the electrical effects of diamide could be reversed by superfusion with normal medium. The results indicate that the retina possesses an active system for maintaining GSH in the reduced state and that this may be essential for the normal function of this tissue.