OXIDANT INJURY IN PC12 CELLS - A POSSIBLE MODEL OF CALCIUM DYSREGULATION IN AGING .2. INTERACTIONS WITH MEMBRANE-LIPIDS

In a model recently developed to study the parameters altering vulnera bility to oxidative stress, it was shown via image analysis that H2O2- exposed PC12 cells exhibited increased levels of intracellular Ca2+ (b aseline), decreases in K+-stimulated Ca2+ levels (peak), and decreased poststimulation Ca2+ clearance (recovery). The present experiments we re performed to determine if the response patterns in these parameters to oxidative stress would be altered after modification of membrane l ipid composition induced by incubating the PC12 cells with 660 mu M ch olesterol (CHL) in the presence or absence of 500 mu M sphingomyelin ( SPH) before low (5 mu M) or high (300 mu M) H2O2 exposure, Neither CHL nor SPH had synergistic effects with high concentrations of H2O2 on b aseline. However, CHL in the presence or absence of SPH reversed the e ffect of low concentrations of H2O2 on baseline. SPH decreased signifi cantly the cell's ability to clear excess Ca2+ in the presence or abse nce of H2O2 and increased significantly the level of conjugated dienes (CDs), It is surprising that in the cells pretreated with CHL, the CD levels were not significantly different from controls. However, in th e presence of SPH, the effects of CHL on CDs were altered. These resul ts suggest that the ratios of membrane lipids could be of critical imp ortance in determining the vulnerability to oxidative stress and Ca2translocation in membranes. This may be of critical importance in agin g where there is increased membrane SPH and significant loss of calciu m homeostasis.