The effect of cooling rate and warming rate on the packing effect in human erythrocytes frozen and thawed in the presence of 2 M glycerol.

The effect of hematocrit (2 versus 75%) has been studied on human red blood cells frozen and thawed in 2 M glycerol at a range of cooling rates (0.8-850 degrees C/min) and warming rates (0.1-200 degrees C/min). The data obtained at a hematocrit of 2% agree well with the data of R. H. Miller and P. Mazur (Cryobiology 13, 404-414, 1976). The results at a hematocrit of 75% show a decrease in recovery with increased cell packing, primarily dependent on warming rate at cooling rates less than 100 degrees C/min and on cooling rate at higher cooling rates. Rapid warming reduced the packing effect, whereas cooling faster than 100 degrees C/min accentuated it. It has been argued that these effects are unlikely to be due to modulation of the generally accepted mechanisms of freezing injury, that is, solution effects and intracellular freezing. It has been suggested that they may be explained by effects of cooling and warming rates on the dimensions of the liquid channels in which the cells are accommodated during freezing and thawing.