Freeze-Etching Studies of Human Platelets

The freeze-etching technique was used to study morphologic features of normal human platelets. A well-developed canalicular system was demonstrated within the platelet, with communication to the plasma surface of the platelets and with direct contact of the canaliculi with organelles. Cross-section fractures of granules revealed compartmentalization in some while others appeared homogeneous. Several types of filamentous structures were observed within the matrix of the platelet. Microtubular subfilaments were approximately 80 Å in diameter. Microfilaments were observed in other areas of platelets and had a diameter of 50-70 Å, a size consistent with that described for actinoid filaments. The interior of the platelet membrane contained 85-Å particles, while the membrane surface had a more granular appearance. Earlier morphologic descriptions of platelets prepared by fixation methods have been confirmed and expanded with this technique.