Fundamental Aspects of the Freezing of Cells, with Emphasis on Mammalian Ova and Embryos

摘要

The problem in cryobiology is how to cool cells to -196 exp 0 C and return them to normal temperatures without killing them. One important factor is the presence of a protective additive like glycerol or dimethyl sulfoxide. Mammalian cells rarely survive freezing to below -40 exp 0 C in its absence. In the presence of an additive, survival is critically dependent on the cooling rate. Supraoptimal rates and suboptimal rates are both damaging. Death at supraoptimal rates is the result of the formation of intracellular ice and its recrystallization during warming. Death at suboptimal rates is a consequence of the major alterations in aqueous solutions produced by ice formation. The chief effects are a major reduction in the fraction of the solution remaining unfrozen at a given temperature and a major increase in the solute concentration of that fraction. The introduction of molar concentrations of additive greatly reduces both the fraction frozen and the concentration of electrolytes in the unfrozen channels and in the cell interior. Usually, freezing either kills cells outright or it results in survivors that retain full capacity to function. But there is the possibility that in some cases survivors may in fact be impaired genetically or physiologically. All evidence indicates that genetic damage does not occur. But there are clear examples in which freezing does induce nonlethal physiological damage. (ERA citation 05:029669)