Freshly trypsinized 3T3 cells send out microspikes of 0.2 μm diameter and up to 10 μm length within 20 min after attachment to a glass substratum. The microspikes move actively and eventually attach to the substratum. Subsequently, lamellae flow out between lines of attached microspikes. If, however, colloidal gold particles of 0.2-0.4 μm diameter and clusters of gold particles up to 4 μm in diameter are placed on the substratum and a microspike attaches to them, we observed two reactions of the microspikes to this contact. They either retract upon contact, transporting the attached particles to the cell surface at a speed of 0.2 μm/sec, or the particles flow toward the cell body while the microspike stays in place. This action results in the clearing of a circular area around each spreading cell before lamellae flow out. "Clearing" proceeds at serum concentrations between 1 and 20% and in concentrations of colchicine up to 20 μm/ml. In concentrations of cytochalasin B higher than 5 μg/ml, however, particle removal is completely inhibited, although the microspikes are still produced by the cell. Transmission electron microscopy shows that the microspikes contain mostly longitudinally oriented microfilaments and only a few microtubules, if any.
ASJC Scopus subject areas
- Cell Biology