Series of tomographic slices and 3D models of tubular granule subtypes. (A) Tomographic slice extracted from a semithin cryosection and reconstructed model showing spherical α-granule with developing extension. (B-C) z-axis orientations through tubular α-granule subtypes obtained from chemical fixed resting platelets. For details, see “Tomography and data analysis.” (B) Fibrillar protein densities (arrows) are apparent within the tubule. (C) Tubular profile connected to a spherical domain. (An animated model is included as supplemental Video 5.) (D) Tomographic slice and 3D model of multiple tubules (light blue) extracted from an approximately 300-nm section of a chemical fixed platelet. (E-F) Tubular and spherical granules extracted from HPF-FS platelets. (E) Several cross-sectioned tubules are shown (arrowheads). (F) Tubule (arrowhead) connected to a spherical granule (☆). White arrowheads indicate (obscured) luminal membranes within α-granule subtypes. Bars represent 100 nm.