4-Hydroxynonenal triggers Ca²⁺influx in isolated rat hepatocytes

Addition of micromolar concentrations of 4-hydroxynonenal (4-HNE), a reactive end-product of lipid peroxidation, to isolated rat hepatocytes was found to cause an early and transient increase in cytosolic Ca²⁺ concentration followed by a more pronounced and progressive elevation. Such a late effect of 4-HNE was prevented by chelation of extracellular Ca²⁺ with EGTA or by the addition of GdCl₃, which is known to block the activity of store operated Ca²⁺ channels in the hepatocyte plasma membrane. Moreover, the preincubation of isolated hepatocytes with the phospholipase C inhibitor U73122 resulted in a complete inhibition of both the early increase of cytosolic Ca²⁺ and the subsequent Ca²⁺ inflow. When 4-HNE was added to the hepatocytes 5 min after the empting of intracellular Ca²⁺ pools by thapsigargin, the aldehyde caused a further increase in the accumulation of Ca²⁺ which was prevented in the presence of GdCl₃. Taken together these results indicate that in hepatocytes 4-HNE causes Ca²⁺ inflow across GdCl₃-sensitive Ca²⁺ channels. The mechanism responsible for such an effect is triggered by the emptying of intracellular Ca²⁺ pools likely resulting from 4-HNE mediated stimulation of phospholypase C, but 4-HNE also appears to interfere with the channel protein(s) or with the mechanism(s) regulating capacitative Ca²⁺ inflow.