Coated membranes in blood platelets.

The simultaneous addition of alcian blue and tannic acid to human blood platelets during glutaraldehyde fixation leads to an excellent representation of coated membranes (CM). Coated membrane segments can be found (1) in plasmalemma, in vesicle system and lysosomal granules, or (2) as coated pits or coated vesicles. They possess the same morphological properties as in other animal cells. An increased number of coated membranes is observed in platelets which have been stimulated with ADP. The role played by coated membranes remains unsolved in contrast to the role of other endomembranes in platelets for instance the vesicle system.