Mechanical and geometrical properties of density-separated neonatal and adult erythrocytes.

Neonatal red blood cells (RBC) show large variations in size, density, and deformability, with a relatively high percentage of neonatal RBC being extremely dense, almost spherical, and poorly deformable. Previous reports suggest that loss of membrane and oxidation of fetal Hb might account for the generation of the dense, rigid RBC in neonates and the shortened life-span of neonatal RBC. To test whether the dense RBC population is particularly fragile and which mechanical properties are responsible for the rigidity of these cells, the following measurements were made for the top (least dense) and bottom (most dense) 3% fractions of density-separated neonatal and adult RBC: cellular deformability (rheoscope); RBC geometry (micropipette system); elasticity, fragility, and viscosity of RBC membrane (micropipette system); Hb solution viscosity (cone-plate viscometer); and selected biochemical parameters. Fetal Hb of neonatal RBC decreased with increasing cell density. When the bottom fractions were compared with the top fractions, neonatal RBC showed a greater reduction in glutamic oxalacetic transaminase activity (72% versus 53%), potassium (39% versus 19%), volume (32% versus 19%), and surface area (42% versus 21%), and a greater rise in density (3.5% versus 1.9%) and mean corpuscular Hb concentration (42% versus 23%) than adult RBC. Cellular deformability in the rheoscope (shear stress 5 Pa) decreased by 24% in adults and by 41% in neonates. Membrane extensional and bending elastic moduli (i.e. membrane deformability) and membrane fragility of neonatal and adult RBC did not significantly change with increasing cell density.(ABSTRACT TRUNCATED AT 250 WORDS)