Water transport and cell survival in cryobiological procedures

Living cells may be cooled to 77 K (liquid nitrogen) either to destroy them selectively or to store them for long periods. Water transport across the cell membranes during freezing and thawing is a primary factor determining whether the cells survive. These water movements are controlled by phase changes both intracellular and extracellular and by other factors such as the nature of any cryoprotective agent present, and the rates of cooling and thawing. The relation between cooling procedure, water transport and cell survival is discussed. In particular, the crucial rôle of dilution shock is emphasized: this is the damage to cells induced during the dilution that occurs both as ice melts during rewarming and when any cryoprotective additives are removed after thawing. Apart from the usefulness of understanding these processes for maximizing preservation or controlling selective destruction, the diverse responses of cells to different combinations of water transport and temperature changes appear likely to provide basic information on the properties of cell membranes.