Ca2+ mobilization is related to the lethal effect of X-irradiation in L5178Y cells

Radiation-resistant L5178Y-R (LY-R) and radiation-sensitive L5178Y-S (LY-S) murine lymphoma cells were X-irradiated and their free Ca2+ concentration was examined with Fura-2 in Ca2(+)-free salt solution. The release of free Ca2+ from intracellular stores was linear between 10 and 60 min after irradiation (1-5 Gy X-rays) and was higher in LY-S than in LY-R cells. Pre-treatment with 2 mM benzamide (Bz) further increased the concentration of free Ca2+ in LY-S cells but not in LY-R cells. In contrast with LY-R cells, LY-S cells had previously been found to be radiosensitized by continuous 2 mM Bz treatment (Szumiel et al. 1984b). Thus, there was a parallel effect of Bz on survival and on the increase in free Ca2+ concentration in LY cells. Moreover, the rates of Ca2+ release after irradiation with 1-5 Gy of X-rays with or without Bz treatment were inversely related to the respective surviving fractions of LY cells.