The bending rigidity of the red blood cell cytoplasmic membrane

An important mechanical property of cells is the membrane bending modulus, kappa. In the case of red blood cells (RBCs) there is a composite membrane consisting of a cytoplasmic membrane and an underlying spectrin network. Literature values of kappa are puzzling, as they are reported over a wide range, from 5 k(B)T to 230 k(B)T. To disentangle the contribution of the cytoplasmic membrane from the spectrin network, we investigated the bending of red blood cell cytoplasmic membranes (RBCcm) in the absence of spectrin and adenosine triphosphate (ATP). We used a combination of X-ray diffuse scattering (XDS), neutron spin-echo (NSE) spectrometry and Molecular Dynamics (MD) simulations. Our results indicate values of kappa of order 4 k(B)T to 6 k(B)T, relatively small compared to literature values for most single component lipid bilayers. We suggest two ways this relative softness might confer biological advantage.