Three-dimensional ultrastructure of in situ membrane skeletons in human erythrocytes by quick-freezing and deep-etching method.

The erythrocyte membrane skeleton is a network of some structural proteins, principally composed of spectrin, actin and protein 4.1, which is also attached to the cytoplasmic surface of the lipid membrane. The purpose of the present review is to describe the three dimensional ultrastructure of in situ membrane skeletons in human erythrocytes. The in situ membrane skeletons are densely organized, and the spectrin itself has a property of extension or contraction with reacting the external mechanical forces. The lengths between the intersections are changed according to the mechanical strength, and also vary even in one erythrocyte. To clarify the in situ organization of membrane skeletons, the quick freezing and deep-etching method should be used for fresh unfixed erythrocytes because of their fragility during preparation steps.