Toxic and osmotic effects of glycerol on human granulocytes

Human granulocytes are damaged by exposure to concentrations of glycerol as low as 0.5 M. We therefore investigated the addition of glycerol to granulocytes and its subsequent dilution under various conditions to try to distinguish between toxic and harmful osmotic effects of glycerol. The lesion caused by glycerol at 0 degree C was expressed as a loss of plasma membrane integrity (as visualized by fluorescein diacetate) only after incubation (greater than or equal to 1 h) at 37 degrees C. This damage was not ameliorated when osmotic stress was lessened by reducing the rates of addition and dilution of glycerol to keep the computed cell volume within 80-170% of isotonic cell volume. However, when osmotic stress was reduced further by increasing the temperature of addition and dilution of glycerol from 0 degree C to 22 degrees C, the tolerance of the cells to 1 M glycerol increased somewhat. Reducing exposure to glycerol to 3 min or less at 0 degree C greatly increased survival, but this time was too short to allow glycerol to equilibrate intracellularly. Finally, the presence of extra impermeant solute (NaCl or sucrose) in the medium to reduce the equilibrium cell volume to 60% of isotonic cell volume enabled granulocytes to survive 30-min exposure to 1 M glycerol at 0 degree C, but cells had to remain shrunken during the 37 degrees C incubation to prevent the loss of membrane integrity. Suspensions that contained damaged granulocytes formed aggregates when incubated at 37 degrees C, and these aggregates were responsible for a major fraction of the observed loss in viability.