Electron microscopical observations on the surface coating of human blood platelets

Abstract

The plasma membrane (trilaminar lipoprotein membrane) of human blood platelets exhibits, in conventional glutaraldehyde—osmium fixation, a layer of an amorphous substance coating its outer surface. The coat has a thickness of about 150–200 . It is considered to be an integral part of the cell membrane, which thus consists of the plasma membrane plus the coating material. The preservation of the coat is much improved if the cationic dye Alcian blue is added to the glutaraldehyde fixative. Ferritin, Thorotrast, and horseradish peroxidase are adsorbed to the coat in vitro. The coat reacts with ruthenium red, colloidal iron, lanthanum ions, and Thorotrast. Its stainability with ruthenium red is abolished by digestion with trypsin and pronase, whereas the stainability with colloidal iron and Thorotrast is not. Platelets incubated with trypsin and soybean trypsin inhibitor show an unimpaired stainability with ruthenium red. It is concluded that the coat probably consists of a sulfated acid mucopolysaccharide and that the coat furnishes the platelet with a zone of interest and with a mechanism for producing rapid changes in the quality of adhesion to surfaces.