The Effect of Diamide on Lens Glutathione and Lens Membrane Function

This content is PDF only. Please click on the PDF icon to access.

Abstract

The physiological role of glutathione (GSH), present in exceptionally high concentration in the lens, has never been clearly delineated. Using ⁸⁶Rb we have studied the cation transport and permeability of rat lenses incubated in vitro with diamide, a relatively specific intracellular GSH oxidant. Lenses incubated without glucose with 0.4 mM. diamide manifest a progressive decrease in GSH with time. In the presence of glucose this effect is minimized, presumably because the GSH level is maintained by the NADPH generated by the pentose shunt mechanism. When lenses are preincubated with diamide without glucose for 2 hours, a 55 to 57 per cent decrease in ⁸⁶Rb uptake is observed. In addition, diamide also effects a 53 per cent increase in the ⁸⁶Rb run-out of lenses incubated without glucose. In the presence of glucose both of these effects are minimized. Incubation with dithioihreitol leads to a small but definite increase in the ⁸⁶Rb uptake of diamide-treated lenses. The observed membrane changes suggest the presence of certain sulfhydryl groups on the lens membrane which are unusally susceptible to oxidation when the GSH level is precipitously reduced. These membrane --SH groups are involved in cation pumping (⁸⁶Rb uptake) as ivell as in determining the degree of membrane permeability (⁸⁶Rb run-out). GSH would be necessary to maintain these --SH groups in the reduced form for proper membrane function.