The influence of membrane skeleton on red cell deformability, membrane material properties, and shape

A membrane skeleton consisting of a structural matrix of spectrin, actin, and band 4.1 linked to band 3 in the fluid bilayer through ankyrin appears to be responsible for many of the material properties of the red cell membrane. In response to externally applied forces, the membrane behaves as a solid, a semisolid, or a liquid, depending on the magnitude and duration of the applied forces. Under physiologic conditions, the normal skeleton permits the red cells to undergo marked reversible deformations as a viscoelastic material. Perturbations of this skeletal assembly, as a result of molecular defects in skeletal components, lead to various altered membrane material properties and altered behavior in the circulation. The altered material properties include increased elastic shear modulus, irreversible membrane flow, or even membrane yield, resulting in cell fragmentation. These alterations in turn lead to changes in cellular deformability either as a result of increased membrane rigidity or decreased surface-area-to-volume ratio, secondary to cell fragmentation. As cellular deformability is one of the major parameters that determines red cell life span, skeletal dysfunction leading to decreases in deformability can account for increased red cell destruction in many congenital and hereditary hemolytic anemias.