Electron microscopic observations on the membrane systems of the rat blood platelet

Abstract Rat blood platelets have two membrane systems in their cytoplasm. One, named the surface connected system (SCS), consists of vacuoles and large cavities which are in continuity with the plasma membrane. The inner surfaces of the membranes of this system have, in common with the plasma membrane, a thin coat of an amorphous substance which probably consists of acid mucopolysaccharides. The other system, named the dense tubular system (DTS), consists of slender membrane‐bound tubules which contain a homogeneous, rather electron dense substance. The DTS is not continuous with the plasma membrane or the SCS. Rat blood platelets incorporate various foreign substances in vivo and in vitro ; these substances are first adsorbed to the amorphous cell coat and subsequently taken into the SCS. It is suggested that the uptake of material by rat blood platelets reflects a membrane flow from the surface membrane to the SCS, and that the process is not phagocytic in nature since segregation and digestion of the incorporated material do not seem to take place.