Late steady increase in cytosolic Ca2+ preceding hypoxic injury in hepatocytes

Upon initiation of hypoxia, the ATP content of hepatocytes in monolayer cultures fell within 5 min from 22 to 12 nmol of ATP/10(6) cells. This decrease in ATP was not followed by early alterations in the cytosolic Ca2+ concentration; for up to 60 min it remained around 100 nM. However, after the period cytosolic free Ca2+ steadily increased, up to 400 nM. This increase began around 60 min before the cells lost their viability, and primarily resulted from an influx of extracellular Ca2+. Likewise, in experiments where the mitochondrial respiratory chain was blocked by KCN and glycolysis was blocked by iodoacetate, the ATP content fell within minutes to 10 nmol/10(6) cells, whereas the cytosolic Ca2+ concentration only began to increase 30 min later (up to 600 nM). However, also under these conditions of 'chemical hypoxia' this increase was clearly (about 10 min) earlier than the loss of viability.