Motions of membrane glycoproteins on the surfaces of locomoting cells

In order to learn more about the mechanism of cell locomotion, membrane protein movements on rapidly locomoting fish epidermal keratocytes have been studied using video-enhanced differential interference contrast microscopy and the technology of single particle tracking (s.p.t.). Information about membrane proteins in random motion has also been obtained using fluorescence photobleaching recovery (f.p.r.).; These studies have provided the first evidence for an active forward transport mechanism that can move glycoproteins to the leading edge of an active lamellipodium. This forward transport is more rapid than either rearward particle transport or the rate of cell locomotion, and can be blocked with cytochalasin D.; Analysis of the motion of diffusing surface proteins has provided evidence that locomotion-related membrane flows do not exist. Thus the membrane passively accompanies the cell, rather than driving cell movement, as had been previously suggested.; Using a laser trap to place latex spheres at specified positions and for specified times on the dorsal surface of locomoting cells, new information has been obtained about the mechanism by which particles are entrained for rearward transport from the cell's leading edge.; The influence of particle size on diffusion in the membranes of living cells has been shown to be insignificant, for particles ranging in size from individual membrane proteins labelled with fluorescent succinyl concanavalin A to concanavalin-A-coated latex spheres 0.55 microns in diameter.; Finally, several novel types of membrane protein movements, not reported previously, and as yet not understood, have been documented.