Effects of subnormal hemoglobin concentration on the deformability of normocytic erythrocytes

Deformability of normocytic hypochromic human erythrocytes was studied as a function of their mean corpuscular hemoglobin content (MCHC). Erythrocyte populations with subnormal MCHC but with normal cell shape and volume and preserved cell surface area, were obtained by incomplete lysis, followed by cell resealing and density gradient separation. Erythrocyte rheological properties were measured in the erythrodeformeter, apparatus in which the erythrocyte laser diffraction pattern is recorded in shear flow. It was found that the deformability index, proportional to the ellipticity of the diffraction pattern at the maximum shear stress, has a negative correlation with MCHC. Membrane elastic shear modulus and membrane surface viscosity have a positive correlation with MCHC. These facts are indicative of a concentration dependent membrane-hemoglobin interaction, and thus hemoglobin concentration must be included as one of the factors influencing erythrocyte deformability, even at low concentrations. We propose a simple model to demonstrate that the maximum oxygen delivery to tissues occurs at the physiological MCHC values.