SURFACE-AREA AND VOLUME CHANGES DURING MATURATION OF RETICULOCYTES INTHE CIRCULATION OF THE BABOON

Changes in the surface area and volume of reticulocytes were measured in vivo during late stage maturation. Baboons were treated with erythr opoietin to produce mild reticulocytosis. Reticulocyte-rich cohorts of cells were obtained from whole blood by density gradient centrifugati on. The cohorts were labeled with biotin, reinfused into the animal, a nd recovered from whole blood samples by panning on avidin supports. C hanges in the surface area, volume, and membrane deformability were me asured using micropipettes during the 2 to 6 weeks subsequent to reinf usion. For the entire cohort, the membrane area decreased by 10% to 15 % and the cell volume decreased by approximately 8.5%, mostly within 2 4 hours after reinfusion. Estimates of the cellular dimensions of the reticulocyte subpopulation within this cohort indicated larger reducti ons in the mean cell area (12% to 30%) and mean cell volume (approxima tely 15%) of the reticulocytes themselves. Two weeks after reinfusion, the distribution of cell size for the cohort was indistinguishable fr om that of whole blood. There was evidence of slightly elevated membra ne shear rigidity in some reticulocytes before reinfusion, but this sl ight increase disappeared within 24 hours after reinfusion. These are the first direct measurements of changes in the membrane physical prop erties of an identifiable cohort of reticulocytes as they mature in vi vo.