Viscoelastic Properties of the Human Red Blood Cell Membrane I. Deformation, Volume Loss, and Rupture of Red Cells in Micropipettes

Single human red blood cells suspended in buffered Ringer's solution were rapidly drawn, at recorded pressures, into glass micropipettes of diameter 0.6–3.2μm. Cells could enter micropipettes of diameter ≥ 2.9μm with minimal pressure. In micropipettes of 0.9–2.9μm, the pressure required increased linearly with decreasing diameter. For diameters 2.5–2.9μm, pressures ranged up to 7cm Hg, and the cells returned to normal biconcave shape on release. For diameters 1.9–2.5μm, the required pressures ranged from 7 to 17cm Hg. The released cells were crenated. In micropipettes 0.9–1.9μm, the pressures required ranged from 17 to 34cm Hg. The cells hemolyzed on entry. As diameter decreased from 0.9 to 0.6μm, cells were drawn into dumbbell shapes and parts of the cells were pinched off without complete hemolysis of the cell. Using an accepted value of 138μm2 for the mean cell area, the mean volume of the human red cell was calculated to be 94μm3. Under mechanical stress, about 12% of this volume is rapidly exchangeable with the external medium. The cell volume may further decrease by 20% which is not reversible