In cells, vesicle transport is driven by motor proteins such as kinesin and dynein, which use the chemical energy of ATP to overcome drag. Using video-enhanced DIC microscopy at 8 frames/s, we find that vesicles in PC12 neurites move with an average velocity of 1.52 0.66 μm/s. The drag force and work required for such steady movement, calculated from Stokes' Law and the zero-frequency viscosity of the cytoplasm, suggest that multiple motors are required to move one vesicle. In buffer, single kinesin molecules move beads in 8-nm steps, each step taking only 50 μs . The effects of such quick steps in cytoplasm, using viscoelastic moduli of COS7 cells, are small . To measure drag forces more directly, we are using B-field-driven magnetic beads in PC12 cells to mimic kinesin-driven vesicles.  Nishiyama, M. et al., Nat. Cell Bio. 3, 425-428 (2001).  Holzwarth, Bonin, and Hill, Biophys J 82, 1784-1790 (2002).
APS Southeastern Section Meeting Abstracts
- Pub Date:
- October 2002