AbstractPretreatment by hypothermic (25°C) cycling (PHC) of attached exponential‐phase V79 Chinese hamster cells by Method 4 (24 hr at 25°C + 1.5 hr at 37°C + 24 hr at 25°C + trypsin + 3 hr at 37°C) or by Method 3 (48 hr at 25°C + trypsin + 3 hr at 37°C) make mammalian V79 cells significantly more resistant to 43°C hyperthermia. There is no significant difference in the 43°C curves whether Method 3 or 4 is used for pre‐exposure. If pre‐exposure is at 15 or 10°C, the resistance to hyperthermia is significantly reduced. PHC by Method 4 significantly increases survival of cells exposed to 5°C and, to a lesser extent, to 10°C. The increase in hyper‐ and hypothermic survival after PHC cannot be accounted for by changes in cell cycle distribution. Heat‐shock protein synthesis is not induced by PHC; hence, protection does not result from newly synthesized proteins. When cells are made tolerant to hyperthermia by a pretreatment in 2% DMSO for 24 hr at 37°C (Method 8), the cells arenotmore resistant to subsequent exposures to hypothermia, either at 5 or 10°C. The results imply that there may be two mechanisms of inducing resistance to hyperthermia, only one of which also confers resistance to hypothermia.
展开▼
