Calcium associated resistance to H2O2 in Chinese hamster V79 cells

To investigate whether the difference in cellular sensitivity of Chinese ha mster V79 and their H2O2-resistant variant cells (Hpr-4) to H2O2 relates to the difference in intracellular Ca2+ concentration in these cells, we meas ured Ca2+ concentration by calcium ion analysis after loading these cells w ith Fura-2/AM. Intracellular Ca2+ concentration increased in both Chinese h amster V79 and Hpr-4 cells as extracellular Ca2+ concentration increased. H owever, the increase in intracellular Ca2+ concentration in response to ext racellular H2O2 was more pronounced in Hpr-4 than V79 cells. H2O2 cytotoxic ity of Hpr-4 but not V79 cells was also decreased in response to the increa se in extracellular Ca2+ concentration. In parallel with the decrease in cy totoxicity in response to increasing extracellular Ca2+ concentration, the frequency of mitochondrial DNA single strand breaks (SSB) in Hpr-4 cells al so decreased without producing observable nuclear DNA SSB. Use of permeabil ized V79 and Hpr-4 cells exposed to H2O2 showed that mitochondrial DNA SSB decreased when extramitochondrial Ca2+ concentration increased. These findi ngs indicate that elevated intracellular Ca2+ concentration may protect aga inst H2O2-induced mitochondrial damage and cytotoxicity ill these cells. (C ) 2000 Elsevier Science Ireland Ltd. All rights reserved.