The Biconcavity of the Red Cell: An Analysis of Several Hypotheses

New evidence is presented to show that the dimple and the annulus of the red cell are not restricted to specific locations on the membrane. This eliminates all but one of the current theories of biconcavity and supports the view that the membrane has unusual mechanical properties such that, although it cannot support surface shear, it can resist both bending and increase in total surface area. The feasibility of such a material is demonstrated by means of a macromodel. The model represents a class of structure that until recently has received little attention but that strongly suggests long-range protein interaction in the membrane surface.