Modification of membrane function, protein synthesis, and heat killing effect in cultured Chinese hamster cells by glycerol and D2O1.

Glycerol and D2O can provide a protective effect to Chinese hamster V79 cells receiving heat treatment. The mechanism for this effect is assumed to be the ability of these agents to stabilize proteins which implies that one of the possible heat-killing mechanisms is the inactivation of a heat-sensitive molecule (protein?). In addition, we observed that heat can alter the membrane permeability rapidly, and glycerol can reduce the initial heat-induced membrane permeability changes (determined by aminoisobutyric acid uptake). Although not as effective as cycloheximide, glycerol and D2O can retard protein synthesis. These two processes can add to the protective effect of stabilizing cellular protein against heat killing. Since glycerol and D2O added during the heat-conditioning period can interfere with the appearance of thermotolerance, the mechanisms for the protective effect of glycerol and D2O are likely to be different from heat-induced thermotolerance. We propose that the heat-sensitive molecule protected by D2O or glycerol may also play a role in the triggering process of the thermotolerance phenomenon. If the conditioning heat treatment is sufficient to affect this molecule but not other cellular targets, thus allowing the cell to survive, thermotolerance may be observed in surviving cells in response to second or continued heat treatment. Depending on the severity of the heat effect, this heat-sensitive molecule may continue to exist after a conditioning heat treatment in medium containing glycerol or D2O, and therefore, the response of the cells to the challenging heat is altered little. This proposed mechanism is capable of explaining several thermotolerance experimental protocols. Since glycerol can also reduce the toxicity of vincristine, microtubule-related protein is probably one of the proteins stabilized by this agent. D2O also probably affects microtubule protein, because the cells heated in medium containing D2O show little topological changes.