LATERAL DIFFUSION IN AN ARCHIPELAGO - SINGLE-PARTICLE DIFFUSION

Several laboratories have measured lateral diffusion of single particl es on the cell surface, and these measurements may reveal an otherwise inaccessible level of submicroscopic organization of cell membranes. Pitfalls in the interpretation of these experiments are analyzed. Rand om walks in unobstructed systems show structure that could be interpre ted as free diffusion, obstructed diffusion, directed motion, or trapp ing in finite domains. To interpret observed trajectories correctly, o ne must consider not only the trajectories themselves but also the pro babilities of occurrence of various trajectories. Measures of the asym metry of obstructed and unobstructed random walks are calculated, and probabilities are evaluated for random trajectories that resemble eith er directed motion or diffusion in a bounded region.