The mechanism of red cell aging. I. Relationship between cell age and specific gravity evaluated by ultracentrifugation in a discontinuous density gradient.

Abstract Rabbit red blood cells were separated in groups of different specific gravity by ultracentrifugation in a discontinuous gradient of isosmotic bovine serum albumin. These fractions were easily separated without mixing by slicing the tube through the albumin layers. The red cells behaved as osmometers, and their specific gravity changed with deviation of the medium from isotonicity. Reproducible results could only be obtained if the osmolality was rigidly controlled. The relationship between red cell specific gravity and age of the cells was evaluated by cohort labeling with glycine-2-C 14 and Fe 59 . The results obtained with Fe 59 were confused by the reutilization of the label. The results obtained with glycine-2-C 14 demonstrated a progressive increase of the red cell specific gravity with age. A comparison was made between ultracentrifugation with and without gradient; the use of the gradient allows density equilibrium to be reached and much sharper age-dependent fractionation. A mathematical model has been elaborated, taking into account the random loss of cells as well as the broad normal distribution of cells in regard to specific gravity, to describe the distribution of red cells of different age at various levels in the gradient. The cell volume was found to be decreased in older cells, but hemoglobin content was unchanged; thus, hemoglobin concentration was found to be increased.