Calcium associated resistance to H₂O₂ in Chinese hamster V79 cells

To investigate whether the difference in cellular sensitivity of Chinese hamster V79 and their H₂O₂-resistant variant cells (Hpr-4) to H₂O₂ relates to the difference in intracellular Ca²⁺ concentration in these cells, we measured Ca²⁺ concentration by calcium ion analysis after loading these cells with Fura-2/AM. Intracellular Ca²⁺ concentration increased in both Chinese hamster V79 and Hpr-4 cells as extracellular Ca²⁺ concentration increased. However, the increase in intracellular Ca²⁺ concentration in response to extracellular H₂O₂ was more pronounced in Hpr- 4 than V79 cells. H₂O₂ cytotoxicity of Hpr-4 but not V79 cells was also decreased in response to the increase in extracellular Ca²⁺ concentration. In parallel with the decrease in cytotoxicity in response to increasing extracellular Ca²⁺ concentration, the frequency of mitochondrial DNA single strand breaks (SSB) in Hpr-4 cells also decreased without producing observable nuclear DNA SSB. Use of permeabilized V79 and Hpr-4 cells exposed to H₂O₂ showed that mitochondrial DNA SSB decreased when extramitochondrial Ca²⁺ concentration increased. These findings indicate that elevated intracellular Ca²⁺ concentration may protect against H₂O₂-induced mitochondrial damage and cytotoxicity in these cells. (C) 2000 Elsevier Science Ireland Ltd.