Cellular Deformability: A Possible Determinant of the Normal Release of Maturing Erythrocytes From the Bone Marrow

In vitro measurements of membrane and whole cell deformability indicate that erythroid maturation is accompanied by a progressive increase in cellular deformability. Early and intermediate normoblasts cannot be entirely deformed into a micropipette with dimensions like those of the apertures in the basement membrane which separates marrow hematopoietic cords from sinuses. Shape and nuclear rigidity are the most important determinants of rigidity in these immature cells. The marrow reticulocyte, with its distinctive clover-leaf configuration, still manifests significant intrinsic rigidity of its membrane and possibly underlying cytoplasm, which may be important to its normal retention in the bone marrow. However, further maturation is accompanied by a progressive decrease in membrane stiffness and, hence, resistance to traversing the micropipette. These results are interpreted to suggest that cellular deformability may be an important determinant of normal release of maturing erythrocytes from the bone marrow.