Survival of frozen-thawed human red cells as a function of cooling and warming velocities

Human red cells were equilibrated for 30 min at 20degreesC in buffered saline containing 2 M glycerol and then frozen to --196degreesC at 0.27, 1.7, 59, 180, 480, 600, and 1300degreesC/min and warmed at 0.47, 1, 26, 160, and 550degreesC/min. Cells frozen at 600 and 1300degreesC/min responded in the classical fashion for cells containing intracellular ice; i.e., survivals were low when warming was slow (less than 10%), but increased progressively with increasing warming rate. The sensitivity to slow warming presumably reflects the recrystallization of intracellular ice. Cells frozen at 59 and 180degreesC/min yielded high survivals at all warming rates. This response is also consistent with the findings for other cells cooled just slowly enough to preclude intracellular ice. Cells frozen very slowly at 0.27 and 1.7degreesC/min, however, responded differently; survivals were considerably higher when warming was slow (0.47 or 1degreesC/min) than when it was 26, 160, or 550degreesC/min. This response is analogous to that observed recently by others in mouse embryos and in higher plant tissue-culture cells and to that observed for many years in higher plants. It also confirms previous observations of Meryman in human red cells. It may reflect osmotic shock from rapid dilution but, if so, the basis of the osmotic shock is uncertain.