Cell ageing for 1 day alters both membrane elasticity and viscosity.

This study was designed to focus on the influences of ageing on membrane elasticity and membrane viscosity. The method used was that of postfusion red blood cell oscillation, since this does not require contact between the cells and a mechanical device to apply reproducible forces to the membrane. Freshly drawn human red blood cells were compared with cells from the same donors drawn 24 h earlier and stored at 20 degrees C. The measurements of the oscillation's first pump event time constant and the first swell phase duration revealed no significant changes between fresh and aged cells. Geometrical cell parameters alone were insufficient to characterise changes in the mechanical membrane properties, since some did not vary significantly whereas others did. On the other hand, measurement of the rates of change of geometrical parameters showed that both the membrane elasticity and viscosity modules were increased after the ageing period. Elasticity and viscosity influences could be separated because the durations of the two phases of the cell oscillations differ by three orders of magnitude. Further evidence is provided that the measurement of mechanical membrane characteristics of aged red blood cell must incorporate measurements of membrane surface properties rather than cell volume properties.