We argue that the paradoxal softness of the red blood cells (RBC) in
fluctuation spectra experiments is apparent. We show that the effective surface
shear modulus μs of the RBC obtained from fluctuation data and that
measured in static deformation experiments have the same order of magnitude. A
simple micromechanical model of the RBC developped for this purpose accounts
for the influence of a finite-thickness cytoskeleton on the fluctuations of the
composite membrane-cytoskeleton system. The spectrin network cytoskeleton with
the bulk shear modulus estimated as μ≈105÷165 Pa contributes to
both normal and tangent fluctuations of the system and confines the
fluctuations of the lipid membrane. The ratio of mean square amplitudes of the
RBC normal and tangent fluctuations / calculated in the frame
of the model is 2-3 orders of magnitude smaller that it is in the free membrane
with the same bending and shear moduliComment: 14 pages, 4 figure
