Electron Microscopy Methods for Studying Platelet Structure and Function

Platelets are very small—the smallest of cellular elements in circulating blood. They lack a nucleus and their cytoplasm is relatively clear. As a result it was impossible to visualize platelets in the crude instruments used by early microscopists. In fact, platelets were not identified until many years after red blood cells and leukocytes were well known (1,2). It took the development of the compound and achromatic microscopes (3) to see platelets, and even then they were considered fragments of erythrocytes or white blood cells (4,5). Difficulties in anticoagulating blood and preparing samples for study in microscopes complicated the problem and delayed for decades the realization that platelets were involved in blood clotting and thrombosis (6). That platelets were critical cellular elements for hemostasis in vivo took even longer (7). It was not until the electron microscope became available that insights into relationships among platelet structure, function, and pathology began to evolve (8,9). Even then, the problems of fixing platelets to preserve their fine structure and relate physical changes following activation to their role in hemostatic physiology took considerable time (10).