Fe 2+ -Induced Lysis and Lipid Peroxidation of Chromaffin Granules

Abstract

Chromaffin granules, the catecholaminergic storage granules from adrenal chromaffin cells, lysed in 10 −9 –10 −7 M Fe 2+ . Lysis was accompanied by the production of malondialdehyde which results from lipid peroxidation. Both chromaffin granule lysis and malondialdehyde production were inhibited by the free radical trapping agent butylated hydroxytoluene but not by catalase and/or superoxide dismutase. The results suggest that lysis resulted from a direct transfer of electrons from Fe 2+ to a component of the chromaffin granule membrane without the participation of either superoxide or hydrogen peroxide and may have resulted from lipid peroxidation. In some experiments, ascorbate alone induced chromaffin granule lysis which was inhibited by EDTA, EGTA, or deferoxamine. The lysis was probably caused by trace amounts of reducible polyvalent cation. Lysis sometimes occurred when Ca 2+ was added with EGTA (10 Μ M free Ca 2+ concentration) and was consistently observed together with malondialdehyde production in the presence of Ca 2+ , EGTA, and 10 Μ M Fe 2+ (total concentration). The apparent Ca 2+ dependency for chromaffin granule lysis and malondialdehyde production was probably caused by a trace reducible polyvalent ion displaced by Ca 2+ from EGTA and not by a Ca 2+ -dependent reaction involving the chromaffin granule.