Protective effect of L-cysteine and glutathione on rat brain Na+,K+-ATPaseinhibition induced by free radicals

The aim of this study was to investigate whether the preincubation of brain homogenates with L-phenylalanine (Phe), L-cysteine (Cys) or reduced glutat hione (GSH) could reverse the free radical effects on Na+,K+-ATPase activit y. Two well established systems were used for the production of free radica ls: 1) FeSO4 (84 mu M) plus ascorbic acid (400 mu M) and 2) FeSO4, ascorbic acid and H2O2 (1 mM) for 10 min at 37 degrees C in homogenates of adult ra t whole brain. Changes in brain Na+,K+-ATPase activity and total antioxidan t status (TAS) were studied in the presence of each system separately, with or without Phe, Cys or GSH. TAS value reflects the amount of free radicals and the capacity of the antioxidant enzymes to limit the free radicals in the homogenate. Na+,K+-ATPase was inhibited by 35-50% and TAS value was dec reased by 50-60% by both systems of free radical production. The enzymatic inhibition was completely reversed and TAS value increased by 150-180% when brain homogenates were preincubated with 0.83 mM Cys or GSH. However, this Na+,K+-ATPase inhibition was not affected by 1.80 mM Phe, which produced a 45-50% increase in TAS value. It is suggested that the antioxidant action of Cys and GSH may be due to the binding of free radicals to sulfhydryl gro ups of the molecule, so that free radicals cannot induce Na+,K+-ATPase inhi bition. Moreover, Cys and GSH could regulate towards normal values the neur al excitability and metabolic energy production, which may be disturbed by free radical action on Na+,K+-ATPase.