MEMBRANE LIPID-PEROXIDATION INDUCES CHANGES IN GAMMA-[H-3]AMINOBUTYRIC ACID TRANSPORT AND CALCIUM-UPTAKE BY SYNAPTOSOMES

In the present study, we analyze the effect of Fe2+/ascorbate-induced lipid peroxidation on Ca2+-dependent and Ca2+-independent release and on the uptake of gamma-[H-3]aminobutyric acid (GA-BA) by sheep brain synaptosomes. In addition, we study the effect of lipid peroxidation on the levels of cytosolic calcium and on the uptake of calcium (Ca-45(2+)). After membrane lipid peroxidation, a decrease in the uptake of GABA is observed. After ascorbate/Fe2+-induced membrane lipid peroxidation, a significant decrease in [H-3]GABA release in response to K+-depolarization occurs, in the absence and in the presence of Ca2+. The influx of Ca-45(2+) induced by K+-depolarization is significantly depressed under peroxidative conditions, while basal calcium uptake is inhibited to a much lesser degree. The levels of free ionic calcium [Ca2+]i, as determined by the fluorescent dye Indo-1, are increased after synaptosomes were submitted to the ascorbate/Fe2+ oxidative stress. It is concluded that membrane lipid peroxidation induces a decrease in Ca2+-dependent and Ca2+-independent efflux of accumulated [H-3]GABA in response to elevated K+ pulses (60 mM) and in the depolarization-induced calcium influx, while free ionic calcium levels increase. The Ca2+-dependent efflux is interpreted to reflect stimulus-secretion coupling process and the Ca2+-independent efflux may reflect membrane transport processes. Thus, the results suggest a possible relationship between a reduced calcium movement across the membrane, the decrease in neurotransmitters uptake and release and oxidative stress.