Red cell deformability in different vertebrate animals

Abstract

In all vertebrates the delivery of oxygen to the tissues occurs via erythrocytes. Yet among vertebrates significant differences exist in the structure and deformability of these cells. The most significant differences exist between mammalian and non-mammalian cells. Non-mammalian red cells contain nuclei and extensive cytoskeletal structures including intermediate filaments and microtubules. Mammalian red cells are anucleate and contain a simple solution of hemoglobin in their interior. Their deformability and stability are completely determined by the mechanical properties of the membrane. Because of these structural differences, nucleated cells are significantly more rigid than anucleate cells. In particular, the marginal band, a microtubular structure at the periphery of nucleated red cells, acts to stabilize these cells against indentations at their rim. The most significant limitation on the deformability of mammalian cells is their limited ability to change either surface area or volume. These constraints place strict limits on the sizes of apertures that these cells can negotiate. Within these constraints, the cellular deformability is limited by the shear elasticity of the membrane. Differences in the size, surface to volume ratio, and membrane elasticity of cells from different animals provide clues to the structural basis and physiologic importance of red cell deformability.