Membrane lipid peroxidation induces changes in γ-[ 3H]aminobutyric acid transport and calcium uptake by synaptosomes

Abstract

In the present study, we analyze the effect of Fe 2+/ascorbate-induced lipid peroxidation on Ca 2+-dependent and Ca 2+-independent release and on the uptake of γ-[ 3H]aminobutyric acid (GABA) 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 ( 45Ca 2+). After membrane lipid peroxidation, a decrease in the uptake of GABA is observed. After ascorbate/Fe 2+-induced membrane lipid peroxidation, a significant decrease in [ 3H]GABA release in response to K +-depolarization occurs, in the absence and in the presence of Ca 2+. The influx of 45Ca 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 [Ca 2+] i, as determined by the fluorescent dye Indo-1, are increased after synaptosomes were submitted to the ascorbate/Fe 2+ oxidative stress. It is concluded that membrane lipid peroxidation induces a decrease in Ca 2+-dependent and Ca 2+-independent efflux of accumulated [ 3H]GABA in response to elevated K + pulses (60 mM) and in the depolarization-induced calcium influx, while free ionic calcium levels increase. The Ca 2+-dependent efflux is interpreted to reflect stimulus-secretion coupling process and the Ca 2+-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.