Post-irradiation exposure to HBSS enhances apoptosis in FM3A cells

Many types of mammalian cells can repair potentially lethal damage (PLD) when incubated in conditioned medium (C-med) or Hank.'s balanced salt solution (HBSS) after irradiation. In this study, we found that there is an increase in clonogenic survival in FM3A cells, mouse mammary carcinoma cells when cells are incubated in C-med, but not in HBSS after irradiation. HBSS was lethal to unirradiated FM3A cells, and apoptosis was observed when cells were exposed to HBSS for more than 10 hours. However, irradiated cells underwent rapid apoptotic cell death and there was a decrease in clonogenic survival when cells were incubated in HBSS for a short time (3 h). Apoptotic cell death, was decreased significantly when irradiated cells were incubated in HBSS with 2% fetal calf serum. In addition, clonogenic survival was decreased significantly when irradiated cells were incubated in C-med with cycloheximide (CHX), an inhibitor of protein synthesis. Thus, the rapid apoptotic death of irradiated FM3A cells induced by HBSS might be due to the absence of serum or inhibition of protein synthesis. Some newly synthesized proteins, or proteins normally found in serum, may be required for irradiated cells to recover from X-ray induced damage.