GEOMETRIC, OSMOTIC, AND MEMBRANE MECHANICAL-PROPERTIES OF DENSITY-SEPARATED HUMAN RED-CELLS

  • 1 January 1982
    • journal article
    • research article
    • Vol. 59  (6) , 1121-1127
Abstract
Although there is evidence that the deformability of the entire red blood cell (RBC) decreases during aging, reports on changes in relevant specific properties associated with the aging process are limited and not in total agreement. Some of the factors that might contribute to this decreased deformability were evaluated. Geometric, osmotic and membrane mechanical properties of unfractionated, top (young) and bottom (old) RBC from 5 healthy adult donors were measured by micropipette techniques. Surface area, volume and diameter of RBC were measured at osmolalities of 297, 254, 202 and 153 mOsmoles/kg. Two membrane mechanical properties, surface shear modulus of elasticity (.mu.) and time constant (tc) of viscoelastic recovery, were studied only in isotonic media. At each of the osmolalities, volume and surface area of the bottom cells were .apprx. 25% lower than those of the top cells. Botton cells showed smaller increases in volume with decreasing osmolality than top cells; the surface area remained constant with changing osmolality for all 3 groups. The surface area-to-volume ration and the minimun cylindrical diameter of the bottom cells were essentially identical to the top cells. However, both the surface area index (actual area of RBC divided by area of a sphere of same volume) and the swelling index (maximal volume divided by actual volume) of the botton cells were significantly lower than top RBC. The shear modulus of elasticity (.mu.) was .apprx. 0.006 dyn/cm in all 3 RBC populations, indicating that the forces necessary to deform a portion of the membrane did not change with RBC aging. The viscoelastic time constant (tc) was 0.148 .+-. 0.020 (SD) s for the botton RBC and 0.099 .+-. 0.017 s for the top cells. This difference indicates that shape recovery following membrane deformation is delayed in old RBC. The membrane surface viscosity (.eta.), calculated as the product of tc times .mu. was 0.95 .+-. 0.22 .times. 10-3 dyn-s/cm for the botton cells and 0.54 .+-. 0.15 .times. 10-3 for the top RBC. The relative deficit in membrane surface area and the increased membrane viscosity of old RBC may be important determinants for their decreased deformatility and their eventual removal from the circulation.