CSPα is membrane-associated and present on both lysosomes and α-granules. (A) WT platelets were immunostained for CSPα (red) and LAMP-1 (green), and imaged using 3-dimensional structured illumination microscopy (3D-SIM). The white lines in the merged images indicate where the profile line analyses were performed. Profile line analyses are shown below the images. (B) WT platelets were immunostained for CSPα (red) and P-selectin (green), and imaged using 3D-SIM. Scale bar, 10 μm for widefield images; 5 μm for cropped images. (C) Resting platelets from CSPα^+/+ and CSPα^−/− mice were isolated and fixed in their resting state. Transmission electron microscopy micrographs were analyzed for platelet shape and granule distribution. Scale bar, 1 μm. (D) Resting platelets from CSPα^+/+ and CSPα^−/− mice were isolated, labeled with 1 μM mepacrine for 30 minutes, and imaged by epifluorescence microscopy to count dense-granule numbers. Scale bar, 5 μm. The number of mepacrine-positive granules was counted and graphed (Mann-Whitney U test, P = .4617). AU, arbitrary units.