HYDROPEROXIDE-INDUCED INCREASES IN INTRACELLULAR CALCIUM DUE TO ANNEXIN-VI TRANSLOCATION AND INACTIVATION OF PLASMA-MEMBRANE CA2-ATPASE()

Oxidative stress can cause changes in intracellular free calcium conce ntration ([Ca2+](i)) that resemble those occurring under normal cell s ignaling. In the alveolar macrophage, hydroperoxide-induced elevation of [Ca2+](i) modulates the respiratory burst and other important physi ologic functions. The source of Ca2+ released by hydroperoxide is intr acellular but separate from the endoplasmic reticulum pool released by receptor-mediated stimuli (Hoyal, C. R., Gozal, E., Zhou, H., Foldena uer, K., and Forman, H. J. (1996) Arch. Biochem. Biophys. 326, 166-171 ). Previous studies in other cells have suggested that mitochondria ar e a potential source of oxidant-induced [Ca2+](i) elevation. In this s tudy we have identified another potential source of hydroperoxide-rele asable intracellular calcium, that bound to annexin VI on the inner su rface of the plasma membrane. Translocation of annexin VI from the mem brane during exposure to t-butyl hydroperoxide matched elevation of [C a2+](i) as a function of time and t-butyl hydroperoxide concentration. The translocation was possibly due to a combination of ATP depletion and oxidative modification of membrane lipids and proteins, A sustaine d increase in [Ca2+](i) occurring > 50 pmol/10(6) cells (50 mu M under these conditions) appeared to be a consequence of membrane Ca2+-ATPas e dysfunction. These results suggest that exposure to oxidative stress results in early alterations to the plasma membrane and concomitant r elease of Ca2+ into the cytosol. In addition it suggests a mechanism f or participation of annexin VI translocation that may underlie the alt erations in macrophage function by oxidative stress.