Interaction of Thermotolerance and Thermosensitization Induced in CHO Cells by Combined Hyperthermic Treatments at 40 and 43°C

Thermotolerance was induced in Chinese hamster ovary cells by heating at 40°C for various times prior to hyperthermia at 43°C. The D0 of the 43°C heat survival curve ( D₀=16.8± 1.5 min) increased about linearly with the duration of pretreatment at 40°C for up to 12 hr at a rate of 10.6 ± 0.7 min/hr of pretreatment. Thermotolerance (in terms of enhanced D0) decayed exponentially with fractionation interval at 37°C; the half-time was 3.8 ± 0.3 hr as determined after conditioning at 40°C for 12 hr. Thermosensitization was observed after priming treatments at 43°C that increased the sensitivity of the cells to a subsequent heating at 40°C by as much as a factor of 100 depending on the duration of pretreatment; e.g., the D0 of the 40°C heat survival curve (43 ± 15 hr) was reduced to 0.43 ± 0.04 hr when a priming treatment at 43°C for 90 min was given prior to heating at 40°C. Thermosensitization decayed exponentially with incubation time at 37°C; the half-time was 2.8 ± 0.3 hr as determined for t...