CET of whole vitrified platelet. (A-B) Snapshots extracted from a whole vitrified platelet in PRP, plunge frozen in liquid ethane. Spherical and extended granule subtypes are shown. (A) Note the difference in electron density of individual spherical granules. Luminal vesicles are visible in the granule on the righthand side of panel A. (B) Tubular profiles (arrowheads) are often connected to electron-dense spherical domains (☆). (C-F) Tomographic slices of a tubular granule subtype extracted from a vitrified platelet after single-axis tilting and low-dose recording at −5 μm defocus. The tubular strand is more than 7 μm long and exhibits a highly curved nature. (G) Reconstructed 3D model (top view) after manual surface rendering with IMOD software. (H) Side view (an animation is included as supplemental Video 6). Bars represent 100 nm.