Iron-induced inhibition of Na+, K+-ATPase and Na+/Ca2+ exchanger in synaptosomes: Protection by the pyridoindole stobadine

The effect of oxidative stress, induced by Fe2+-EDTA system, on Na+,K+-ATPase, Na+/Ca2+ exchanger and membrane fluidity of synaptosomes was investigated. Synaptosomes isolated from gerbil whole forebrain were incubated in the presence of 200 mu M FeSO4-EDTA per mg of protein at 37 degrees C for 30 min. The oxidative insult reduced Na+,K+-ATPase activity by 50.7 +/- 5.0 % and Na+/Ca2+ exchanger activity measured in potassium and choline media by 47.1 +/- 7.2 % and 46.7 +/- 8.6 %, respectively. Membrane fluidity was also significantly reduced as observed with the 1,6-diphenyl-1,3,5-hexatriene probe. Stobadine, a pyridoindole derivative, prevented the decrease in membrane fluidity and in Na+/Ca2+ exchanger activity. The Na+,K+-ATPase activity was only partially protected by this lipid antioxidant, indicating a more complex mechanism of inhibition of this protein. The results of the present study suggest that the Na+/Ca2+ exchanger and the Na+,K+-ATPase are involved in oxidation stress-mediated disturbances of intracellular ion homeostasis and may contribute to cell injury.