Erythrocyte membrane elasticity, fragmentation and lysis
The intrinsic material behavior of the normal human erythrocyte membrane may be characterized in terms of its deformation and rate of deformation response as result of forces applied to the membrane. The intrinsic properties are defined by μ, the elastic shear modulus reflecting recoverable hyperelastic response; nu, shear viscosity defining viscoelastic behavior with internal viscosity energy dissipation; T0, a yield shear indicating the elastic limit of the membrane material; and nu(p), shear viscosity in the plastic domain, i.e., irrecoverable extension after the elastic limit of the membrane has been exceeded. Experimental values for these constants for normal membranes are: μ = 10-2 dyn/cm; nu = 10-4 dyn.s/cm; T∞ = 2x10-2 dyn/cm; and nu(p) = 10-2 dyn s/cm. The area compressibility modulus, the constant reflecting resistance to compression or dilation of this two-dimensional membrane is high, 300 dyn/cm, and the maximum fractional area expansion which produced lysis is 2 to 4%. Removal of spectrin from the membrane decreases the elastic constant and tension for lysis, whereas modification of glycophorin and other intrinsic membrane proteins does not affect the solid material behavior. Cross-linking agents such as glutaraldehyde (0.008%) increases the elastic constant; this parallels relative inelasticity of the senescent human erythrocyte membrane and suggests a model for membrane senescence. Minimum tension for membrane fragmentation is equal to the yield shear - 0.02 dyn/cm. 'Rapid' fragmentation in a micropipette occurs at 0.4 dyn/cm which is still three orders of magnitude less than that for lysis. Also, the calculated change in membrane free energy for micropipette fragmentation is three orders of magnitude less than that for lysis.
Lacelle, PL; Evans, EA; Hochmuth, RM
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