Erythrocyte aggregation: the roles of cell deformability and geometry

The sedimentation rate of erythrocyte under controlled conditions was used to study the influence of cell deformability and geometry on erythrocyte aggregation. The cell deformability, which is determined by the viscoelastic properties of the membrane, the cell geometry, and the cellular viscosity, was systematically altered. The viscoelasticity of the membrane was gradually decreased with increasing concentrations of glutaraldehyde (0.01-1.0%) or heat treatment at 47.5 degrees C for increasing time intervals (0-80 min), which led to an increase at low concentrations and short incubation and then to a progressive decrease of erythrocyte aggregation. Changes of the osmolality were used to simultaneously alter the cell geometry and cellular viscosity in opposing directions. When the haematocrit level was held constant, the sedimentation rate decreased with increasing osmolality. With a constant erythrocyte number per volume, but changing haematocrit level, the highest sedimentation rate was observed at isotonicity. These results indicate that cell deformability and geometry play an important role in erythrocyte aggregation and sedimentation and may have implications on other cell-cell interactions as well.