Deformability of isolated red blood cell membranes.

We have used a laser diffraction method (ektacytometry) to directly measure the membrane component of red cell deformability, without contributions from either cell geometry or internal viscosity. This technique was validated by subjecting resealed erythrocyte ghosts to manipulations previously shown to increase the membrane shear modulus. Heating above 45 degrees C, pH greater than 9.0 and less than 5.0, and micromolar concentrations of the cross-linking agents, glutaraldehyde and diamide, all reduced the deformability of resealed erythrocyte ghosts. We have applied this assay to the study of reduced cellular deformability of calcium-loaded red cells, and have shown that, for physiological concentrations of calcium, the effect of calcium on the physical properties of the membrane may be negligible when compared to its effect of promoting cell dehydration and subsequent increased cytoplasmic viscosity.