Lamellar bodies in activated platelets as revealed by the use of tannic acid and a comparison with the concentric laminar organelles of type II pneumocytes.

Transmission electron micrographs of unactivated platelets, adenosine diphosphate-induced platelet aggregates and thrombin-induced platelet clots, prepared using a tannic acid fixative/stain, reveal characteristic lamellar bodies. These lamellar bodies are seen more frequently in the clots. The lower limit of the dark band periodicity in the lamellar bodies is between 4 . 4 and 5 . 0 nm, and the layers are thought to be composed of phospholipid, probably phosphatidyl choline. Analogies are drawn between the lamellar bodies of platelets and the concentric laminar organelles present in Type II pneumocytes (dust cells) which show similar ultrastructural characteristics when treated with the tannic acid fixative/stain.