Organelles and granules continue to translocate in the presence of actin toxins. (A-F) Cytochalasin and latrunculin treatment significantly reduce phalloidin staining in proplatelets. Comparison of (A,C,E) antitubulin immunofluorescence in red to corresponding (B,D,F) phalloidin staining in green of control, cytochalasin D-, and latrunculin A-treated cells. Note that the actin-disrupting agents decreased the level of F-actin in proplatelets as visualized by phalloidin staining. (G-P) Mitochondria/granule distribution in megakaryocytes treated with actin toxins. Comparison of (G,I,K,M,O) antitubulin fluorescence (green) versus (H,J,N) anti-von Willebrand factor or (L,P) antiserotonin fluorescence (red) of proplatelets in (G-H) control, (I-L) cytochalasin B-treated, or (M-P) latrunculin A-treated megakaryocytes. Organelles/granules continue to disperse along the length of the proplatelets. Scale bars, 5 μm. (Q-S) Organelles translocate in proplatelets and are trapped at the tips following latrunculin A treatment (Movie S5). (Q) Fluorescence micrograph of a living megakaryocyte labeled with MitoTracker Green after treatment with 2 μM latrunculin A for 2 hours. Scale bar, 5 μm. (R) Images of the proplatelet tip (in the boxed region) taken every 10 minutes are shown. The arrows indicate mitochondria that translocate and enter the proplatelet tip but do not exit at the same frequency. A large amount of mitochondria are observed to cumulate at the bud node of the bulbous tip. (S) Comparison of the percentage of organelles/granules (an equal number of mitochondria, α-granules, and dense granules were followed) that enter and exit proplatelet swelling and tips.