A permeabilized proplatelet system to study organelle transport. (A-B) Megakaryocyte organelles move along permeabilized proplatelet microtubules. (A) DIC micrograph of a permeabilized proplatelet. (B) DIC time-lapse sequence showing megakaryocyte organelle movement along the immotile microtubules of a permeabilized proplatelet from the boxed region in panel A (Movie S8). The sequence demonstrates an organelle attached to the microtubule cytoskeleton of a permeabilized proplatelet (arrowhead at 0 sec) and moves downward in the direction of a stationary particle attached to the immotile microtubules. Frames are every 5 seconds. Scale bar, 5 μm. (C-E) Polystyrene latex beads attached to permeabilized proplatelets move with sliding microtubules. Uncoated latex polystyrene beads were attached to Triton X-100 permeabilized proplatelets. The beads remain stationary until the addition of ATP. Microsphere transport began when the preparation was perfused with 1 mM ATP (0 seconds). Scale bars, 5 μm. All beads marked with arrowheads moved relative to the stationary marker, labeled with an arrow. (C,E) Differential-interference-contrast micrograph of proplatelets following permeabilization with Triton X-100 in a microtubule-stabilizing buffer containing taxol. (D) High magnification video sequence of 3 uncoated latex beads (arrowheads) moving on the microtubule cytoskeleton of a permeabilized proplatelet (Movie S9). Beads moved in tandem, as though they were mechanically linked. (F) High magnification video sequence of 2 beads attached to a sliding microtubule (Movie S10). Both beads move approximately 5 μm, demonstrating tandem movements along the same microtubule.