Microinjected fluorescent polystyrene beads exhibit saltatory motion in tissue culture cells.

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Abstract
Microinjected 0.26-.mu.m fluorescent, carboxylated microspheres were found to display classical saltatory motion in tissue culture cells [BS-C-1 and PtKl]. The movement of a given particle was characterized by a discontinuous velocity distribution and was unaffected by the activity of adjacent particles. The microspheres were translocated at velocities of up to 4.7 .mu.m/s and somtimes exhibited path lengths > 20 .mu.m for a single saltation. The number of beads injected into a cell could range from a few to over 500 with no effect on the cell''s ability to transport them. Neither covalent cross-linking nor preincubation of the polystryene beads with various proteins inhibited the saltatory motion of the injected particles. The motion of the injected beads in cultured cells was reversibly inhibited by the microtubule poison nocodazole, under conditions in which actin-rich, nitrobenzoxadiazol-phallacidin-staining structures remain intact. Whole-cell high voltage EM of microinjected cells that were known to be moving the fluorescent microspheres revealed that the beads were embedded in the cytoplasmic matrix and did not appear to be membrane bound. The enhanced detectability of the fluorescent particles over endogenous organelles and the ability to modify the surfaces of the beads before injection may enable more detailed studies on the mechanism of saltatory particle motion.