Inhibition of store-operated calcium entry in human lymphocytes by radiation: Protection by glutathione

The influence of gamma radiation on basal compared to activation-dependent Ca2+ influx in human lymphocytes was investigated. a new quantitative fluorescence technique termed differential ratiometric fluorescence spectroscopy (DRFS) was employed. DRFS facilitated the real-time detection of changes in fluorescence in experimental and control cell samples simultaneously, enabling the resolution of acute moderate changes (congruent to 10-30%) in Ca2+ (manganese) influx after exposure to ionizing radiation and other oxidant interventions. Exposure to radiation inhibited thapsigargin-stimulated store-operated Ca2+ influx but not basal Ca2+ inflow in Jurkat T cells and human peripheral blood lymphocytes. The response of store-operated Ca2+ influx to gamma radiation was dependent on dose between 5 and 40 Gy and was inhibited by preincubation with the Ca2+ channel blocker Ni2+, as determined with Jurkat T cells. Elevation of the intracellular concentration of glutathione significantly reduced the inhibition of Ca2+ influx by gamma radiation. Similar to radiation, both the superoxide anion-generating xanthine/xanthine oxidase system and hydrogen peroxide inhibited thapsigargin-stimulated Ca2+ influx in Jurkat T cells, and this inhibition was reversed in the presence of the antioxidant N-acetyl-L-cysteine, In conclusion, (1) ionizing radiation inhibited store-operated Ca2+ entry in human lymphocytes,(2) the sensitivity of Ca2+ influx to radiation was strictly dependent on depletion of Ca2+ stores, and (3) glutathione protected against the inhibition of store-operated Ca2+ entry by gamma radiation. (C) 1999 by Radiation Research Society.