Lipid and protein contribution to red blood cell membrane viscoelasticity

Abstract

The relationship between molecular structure and red blood cell (RBC) membrane viscoelasticity was investigated. To define the contribution of lipids to membrane viscoelasticity, we modified membrane cholesterol content and lipid fluidity. To determine the role of the protein skeleton on the cytoplasmic side of the membrane we used RBCs with a molecular defect of the spectrin molecule (type I hereditary elliptocytosis). Treatment of normal erythrocytes with N-ethyl-maleimide (NEM) resulted in RBCs with the same structural defect of the spectrin molecule. We compared the membrane viscoelasticity of these NEM-treated-RBCs to that of elliptocytes. To assess the role of the hemoglobin layer associated with the membrane we studied the viscoelasticity of young and old RBCs. The membrane viscoelasticity was determined by the micropipette test. Membrane lipid fluidity was estimated by fluorescence depolarization. Results indicated that lipid composition and fluidity were not determinants of RBC membrane viscoelasticity. However our results showed that the viscoelastic properties of the RBC membrane are affected by a specific change in the state of membrane spectrin. The membrane mechanical behavior of old RBCs suggested that the hemoglobin associated with the membrane might influence the viscous response to membrane deformation.

This work demonstrates that integrity and stability of the protein network are essential to the mechanical function, while modification of the lipid core does not affect membrane viscoelasticity. These findings are important when therapies are designed to improve RBC rheology in pathological conditions: the membrane skeleton should be the main target.