Heat protection by glycerol in vitro.

Heating of either Chinese hamster ovary or HeLa cells in medium containing glycerol protected against thermal killing. Above glycerol concentrations of 100 mM, protection of Chinese hamster ovary cells increased in a concentration-dependent manner. Exposure to glycerol only, before or after heating at 45 degrees, did not protect against cell killing. Glycerol protection against thermal damage was also expressed at the subcellular level. The fractional increase in the protein:DNA ratio for nuclei from heated HeLa cells (15 min, 48 degrees) was 1.6 with heating in 1 M glycerol, compared to 2.0 for medium controls. Both glycerol (1 M) and heat-induced thermotolerance (4 hr, 41.5 degrees) partially reversed the sensitizing effects of pH 6.4 and stepdown heating at 41.5 degrees. The partial deprivation of nutrients achieved by incubating cells in Hanks' balanced salt solution-sensitized Chinese hamster ovary cells against 45 degrees hyperthermia. Glycerol reversed this sensitization but only when nutrient deprivation was short term (75 min). With a long-term, 8.5-hr exposure to glycerol in Hanks' balanced salt solution, cells were significantly more sensitive to heat killing at 41.5 degrees than were cells heated for an equal period in Hanks' balanced salt solution alone. The similarities in the characteristics of glycerol protection and heat-induced thermotolerance suggest a common mechanistic basis for the two phenomena, although the ability of glycerol to act as a sensitizer in nutrient-deprived cells is not understood.