Thermal tolerance during S phase for cell killing and chromosomal aberrations.
Synchronous Chinese hamster ovary cells in early S phase were obtained by selecting mitotic cells, accumulating them at the G1/S border by incubating them in aphidicolin for 12 h, and then incubating them for 2 h after releasing them from the aphidicolin block. To determine if thermotolerance could be induced, the cells were heated at 43 degrees C for 20 min in early S phase, incubated for 160 min, and then heated a second time at 43 degrees C for different durations (30-100 min). For the control, nontolerant population, the cells in early S phase were incubated for 50 min and then heated once at 43 degrees C for different durations (20-60 min). Flow cytometric analysis indicated that the population receiving the second heat dose was in the same part of S phase as the population receiving the single heat dose. A comparison of the heat response for the two populations indicated that heating during early S phase induced thermotolerance for both cell killing and chromosomal aberrations; i.e., for 10% survival, which corresponded to 10% of the cells being cytologically normal, the thermal dose was twofold greater in the thermotolerant cells than in the control, nontolerant cells. Furthermore, this thermotolerance developed during S phase. These observations support the hypothesis that heating during S phase kills cells primarily by inducing chromosomal aberrations.
Li
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XL
Radiation Oncology Research Laboratory, University of California, San Francisco 94143-0806.
Wong
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RS
Dewey
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WC
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured / Q000166:cytology; D002869:Chromosome Aberrations; D006224:Cricetinae; D003412:Cricetulus; D006358:Hot Temperature; D066298:In Vitro Techniques; D007399:Interphase