Effects of freezing on the hyperthermic survival of tissue culture cells.

The survival rate of V79 Chinese hamster lung fibroblasts treated with heat and freezing was investigated. The hyperthermic behavior of these cells was similar to other reports; Thermotolerance was observed below 43 degrees C during continuous heating. There was no difference in survival rate whether the cells were heated while attached to tissue culture flasks or in suspension, although the pH of the medium during the latter situation could be around 8.2 during hyperthermic treatment. If the cells were frozen and thawed before heating, the pattern of survival did not change significantly from that of heating alone, and thermotolerance was still observed below 43 degrees C. The Arrhinius plot of heat sensitivities between 41 and 45 degrees C demonstrated a straight line, giving an activation energy of 171 kcal/mole. A break on the plot around 42.5 degrees C could not be located, probably due to the lack of experimental points. If the cells were frozen and thawed immediately after heating, the survival rate was lower than that expected from considering hyperthermia and freezing as two independent processes. Possible explanations are provided in the result and discussion section.