The operation of Na⁺/Ca²⁺ exchanger prevents intracellular Ca²⁺ overload and hepatocyte killing following iron-induced lipid peroxidation

Stimulation of lipid peroxidation by incubating isolated rat hepatocytes with ADP/FeCl₃ caused a time dependent increase in cytosolic free Ca²⁺ levels, without influencing cellular Na⁺ content. Omission of Na⁺ from the incubation medium greatly increased the accumulation of Ca²⁺, which was partially reverted upon transferring the cells in a Na⁺ containing medium. This suggested that a Na⁺-dependent Ca²⁺ transporter was activated upon the elevation of cytosolic Ca²⁺ and partially counteracted the influx of Ca²⁺ promoted by lipid peroxidation. In the presence of Na⁺ cell death was not associated with the increase of Ca²⁺ induced by peroxidative injury; however, decrease of mitochondrial membrane potential and loss of cell viability followed the massive accumulation of Ca²⁺ occurring in hepatocytes incubated with ADP/FeCl₃ in a Na⁺-free medium. Both these effects were completely prevented by chelation of extracellular Ca²⁺ with EGTA. Thus, we conclude that Na⁺-dependent Ca²⁺ transporter is involved in controlling excessive accumulation of Ca²⁺ induced by stimulation of lipid peroxidation and can prevent hepatocyte death caused by Ca²⁺-dependent alterations of mitochondrial activity.