Membrane ion transport systems during oxidative stress in rodent brain: Protective effect of stobadine and other antioxidants

The effect of oxidative stress in vitro induced by radical generating syste ms (RGS) (Fe2+-EDTA and Fe2+-EDTA plus H2O2) On synaptosomal and microsomal ion transport systems as well as on the membrane fluidity was investigated . Oxidative insult reduced Na+, K+-ATPase activity by 50.7 % and Na+-depend ent Ca2+ uptake measured in choline media by 46.7%. Membrane fluidity was a lso significantly reduced as observed with the fluorescent probe. Stobadine (ST) prevented the decrease in membrane fluidity and Na+-dependent Ca2+ up take, however Na+, K+-ATPase activity was only partially protected, indicat ing a more complex mechanism of inhibition. Incubation of microsomes with R GS led to the loss of ability of membranes to sequester Ca2+, as well as to the decrease of Ca2+-ATPase activity and to the increase of Ca2+ permeabil ity to 125.1%. The relative potency of the two RGS to decrease membrane flu idity correlated well with the system's potencies to induce lipid peroxidat ion. The extent of protection against depression of Ca2+ uptake values and Ca2+-ATPase activity by membrane soluble antioxidants (U-74500A, U-83836E, t-butylated hydroxytoluene-BHT and ST) was dependent on the experimental co nditions and on the dose and nature of antioxidant used. ST seems to be at least as affective as BHT and 21-aminosteroids, and more potent than tocoph erol acetate. Water soluble glutathione had no significant effect on the RG S induced inhibition of Ca2+-ATPase activity. Combination of ST with glutat hione enhanced ST antioxidant efficacy, so drug combination might be benefi cial therapeutically.