The response of multilamellar liposomes to freezing and thawing

The use of liposomes as a model system for investigating the mechanism of freezing injury was investigated. Modification of the liposome phospholipid and cholesterol content allows a correlation to be made between the composition of a membrane system and its response to the stresses of freezing and thawing. The data on phase transitions are contradictory in the sense that liposomes become more sensitive to freezing injury following treatments which both increase or decrease phase transition temperature. In contrast the effect of cholesterol in sensitizing membranes to the stresses of freezing and thawing appears to be more fundamental. Direct cryomicroscope observations of liposomes during slow cooling indicate that they are osmotically active at low temperatures and upon thawing morphological alterations to the membranes occur. The response of liposomes following cooling at a range of rates to ?196 °C and the effects of cryoprotective additives are similar to those observed with many cell types. These results indicate that liposomes are a valid model for investigating the biochemistry of membrane damage induced by the stresses of freezing and thawing.