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 Ca(2+) 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 with10-30%) in Ca(2+) (manganese) influx after exposure to ionizing radiation and other oxidant interventions. Exposure to radiation inhibited thapsigargin-stimulated store-operated Ca(2+) influx but not basal Ca(2+) influx in Jurkat T cells and human peripheral blood lymphocytes. The response of store-operated Ca(2+) influx to gamma radiation was dependent on dose between 5 and 40 Gy and was inhibited by preincubation with the Ca(2+) channel blocker Ni(2+), as determined with Jurkat T cells. Elevation of the intracellular concentration of glutathione significantly reduced the inhibition of Ca(2+) influx by gamma radiation. Similar to radiation, both the superoxide anion-generating xanthine/xanthine oxidase system and hydrogen peroxide inhibited thapsigargin-stimulated Ca(2+) 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 Ca(2+) entry in human lymphocytes, (2) the sensitivity of Ca(2+) influx to radiation was strictly dependent on depletion of Ca(2+) stores, and (3) glutathione protected against the inhibition of store-operated Ca(2+) entry by gamma radiation.
Killoran
P L
PL
Bioelectromagnetics Laboratory, Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California 94305-5304, USA.
Walleczek
J
J
D000111:Acetylcysteine / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002588:Cesium Radioisotopes; D005720:Gamma Rays; D005978:Glutathione / Q000502:physiology*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D019169:Jurkat Cells; D008214:Lymphocytes / Q000502:physiology / Q000528:radiation effects*; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D013050:Spectrometry, Fluorescence / Q000295:instrumentation / Q000379:methods; D013481:Superoxides / Q000494:pharmacology; D013601:T-Lymphocytes; D019284:Thapsigargin / Q000494:pharmacology; D008063:Thioctic Acid / Q000494:pharmacology
D000975:Antioxidants; D002588:Cesium Radioisotopes; D013481:Superoxides; D008345:Manganese; D019284:Thapsigargin; D008063:Thioctic Acid; D006861:Hydrogen Peroxide; D005978:Glutathione; D002118:Calcium; D000111:Acetylcysteine