Newly formed platelets possess granules and an elaborate microtubule network. (A) Thin section TEMs of representative platelets at baseline (i,vi,vii) and after 6 hours in culture (ii-v,viii). The black scale bar represents 500 nm. Multiple α granules (black arrows) are observed in platelets with multiple cell bodies (iii-v) and occasionally in the connecting region (iii). A constricted region resembling a cleavage furrow is noted along the long shaft of a cultured platelet (v with inset, original magnification ×80 000; scale bar represents 100 nm). Original magnifications: iii, ×25 000; iv-v, ×30 000. Microtubules in cross section were also observed at ends of the cultured platelets (viii white arrows). (viii) How platelet diameters were measured by TEM (original magnification ×30 000), which confirmed that cell diameters significantly (P < .05) increased in cultured platelets compared with freshly isolated platelets (also see Figure 5Ai). (B) The panels display baseline platelets (far left) and cultured platelets (6 hours) that were left alone or treated with reagents that disrupt microtubular function (ie, nocodazole or taxol). Top row: Specific immunostaining for β-tubulin. Bottom row: Corresponding transmission images. This figure is representative of 3 independent experiments. Scale bars represent 10 μm.