The shape of the human red blood cell (RBC) is known to be a biconcave disc. The experiments in this paper identify some of the underlying determinates. RBC ghosts were made such that they were spheres in hypo-osmotic solutions and biconcave discs in iso-osmotic solutions. The spherical ghosts were centrifuged onto coverslips. When these spheres became biconcave discs by flushing with an iso-osmotic solution, the ghosts laid flat on the coverslip. This indicates that, during centrifugation, the spherical ghosts were oriented by a dense band in their equatorial planes. This unique orientation appears to be the first evidence that differences in the densities between the rim and the dimple regions of RBCs and their ghosts underlie their biconcave shape.

Abstract

The shape of the human red blood cell is known to be a biconcave disk. It is evident from a variety of theoretical work that known physical properties of the membrane, such as its bending energy and elasticity, can explain the red-blood-cell biconcave shape as well as other shapes that red blood cells assume. But these analyses do not provide information on the underlying molecular causes. This paper describes experiments that attempt to identify some of the underlying determinates of cell shape. To this end, red-blood-cell ghosts were made by hypotonic hemolysis and then reconstituted such that they were smooth spheres in hypo-osmotic solutions and smooth biconcave discs in iso-osmotic solutions. The spherical ghosts were centrifuged onto a coated coverslip upon which they adhered. When the attached spheres were changed to biconcave discs by flushing with an iso-osmotic solution, the ghosts were observed to be mainly oriented in a flat alignment on the coverslip. This was interpreted to mean that, during centrifugation, the spherical ghosts were oriented by a dense band in its equatorial plane, parallel to the centrifugal field. This appears to be evidence that the difference in the densities between the rim and the dimple regions of red blood cells and their ghosts may be responsible for their biconcave shape.