NOTE: Text or symbols not renderable in plain ASCII are indicated by .... Abstract is included in .pdf document. A procedure for preparing and fractionating linear density gradients of bovine serum albumin is described. Reproducible buoyant density distributions of human erythrocytes in these gradients were obtained and individual fractions could be rebanded. The average buoyant density of erythrocytes from four individuals was 1.0808 plus or minus 0.0004 g. cm.superscript -3; the average density from a fifth individual was 0.0028 g. cm.superscript -3 greater. The entire buoyant density distribution shifts with salt content; the erythrocytes behave as "perfect" osmometers. Salt gradients predictably spread or narrow the distribution, and may be used to increase the resolving power of the density gradient. Rabbit erythrocytes pulse-labeled with Fesuperscript 59 first appear at the light edge of the distribution, and the mean progresses linearly with time through the distribution. The width of the distribution of labeled cells also increases with time. A study with the Coulter-Counter Model B of cell volumes in the buoyant density fractions showed that the mean cell volumes on the lighter side remained constant, while on the dense side the mean cell volume decreases. This decrease, if regarded as a water loss, does not quantitatively account for the increase in density. Microscopic examination of the individual fractions of the buoyant density distribution show that the cells do not appear to be damaged by the manipulations, and that cells in the denser fractions are significantly less biconcave than the average cell. The reticulocytes concentrate in the lighter fractions, but do not clearly separate from the erythrocytes. It is proposed that the buoyant density be regarded as an index of the physiological condition of the erythrocyte. A summary discussion of the aging of the erythrocyte is given.
Leif et al. (1964) studied this question.