Chinese hamster ovary cells exposed to the sulfhydryl compound cysteamine combined with heat treatment at 44°C developed thermotolerance within 8 h. After initial treatment either with 15 min cysteamine (0.4 mm) at 37°C immediately followed by 15 min heat at 44°C or with 15 min cysteamine (0.4 mm) at 44°C, the magnitude of thermotolerance developed was identical. The D0 of the subsequent 44°C heat survival curves increased by factors of 8.9 and 7.9, respectively. The kinetics of thermotolerance induction and the time to reach the maximum of thermotolerance expression after combined cysteamine treatment at 44°C for 15 min was found to be comparable to the effects of 44°C treatment alone for 30 min. The synergistic effect of cysteamine with the conditioning heat treatment at 44°C was blocked by catalase (50 µg/ml).

Following initial treatment with cysteamine at 37°C, cells became thermotolerant within 2 h. The D0 of the survival curves for 44°C heat treatments increased with duration (t1 = min, 37°C) of the cysteamine (0.4 mm) exposure; e.g., the D0 increased by factors of 1.5, 1.6, 2.2, and 2.6 for t1 = 30, 60, 90, and 120 min. The induction of thermotolerance by cysteamine at 37°C was completely blocked by the addition of catalase (50 µg/ml), present during the initial period of drug treatment.

Combined cysteamine and heat treatment at 44°C, but also cysteamine exposure at 37°C, enhanced synthesis of heat shock proteins. The data suggest that oxidative stress by cysteamine can be synergistic with the conditioning heat treatment at 44°C which induces thermotolerance. At 37°C, cysteamine itself induces thermotolerance and the enhanced synthesis of heat shock proteins under these conditions.

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This work was supported in part by Grant Is 31/2-1 from the Deutsche Forschungsgemeinschaft and by Grant CA 31397 from the USPHS. Part of this work was presented at the 33rd Radiation Research Society Meeting, Los Angeles, CA, May 1985.

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