| Abstract: | The response of LI A2 cells in vitro to water bath hyperthermia was investigated. In previous studies in the temperature range 40–5–45 0°C., an Arrhenius plot for heat killing of L1A2 cells was linear, and thermotolerance did not develop during continuous heating. The present Arrhenius analysis was extended to the range 38–45°C., and the Arrhenius plot was biphasic with an inflection point at 40–5°C., below which the activation energy was significantly increased from 724 to 923 kJ/mol (P< 0 001). In order to test for the development of thermotolerance during continuous heating, the cells were heated in the range 38–41°C for 10 h, followed immediately by a graded test treatment at 42°C. Thermotolerance developed below 40–5°C as shown by an increased D0 of the 42°C survival curve, but not at 40 5 and 4FC. Preheating for 90min at 42°C followed by a 10 h incubation at 37°C resulted in maximal thermotolerance with a thermotolerance ratio of approximately 4–3, a ratio also obtained if the cells were incubated for 10 h at temperatures of 38–40°C. No thermotolerance was observed at incubation temperatures of 40 5°C and above. Thus, in the L1A2 cells 40°C is the upper temperature permissive for thermotolerance development, and the data support the assumption that the inflection point on the Arrhenius plot reflects the upper limit for thermotolerance development. |
