SINGLE-PARTICLE TRACKING - EFFECTS OF CORRALS

Structural proteins of the membrane skeleton are thought to form ''cor rals'' at the membrane surface, and these corrals may restrict lateral diffusion of membrane proteins. Recent experimental developments in s ingle-particle tracking and laser trapping make it possible to examine the corral model in detail. Techniques to interpret these experiments are presented. First, escape times for a diffusing particle in a corr al are obtained from Monte Carlo calculations and analytical solutions for various corral sizes, shapes, and escape probabilities, and reduc ed to a common curve. Second, the identification of corrals in trackin g experiments is considered. The simplest way to identify corrals is b y sight. If the walls are impermeable enough, a trajectory fills the c orral before the diffusing particle escapes. The fraction of distinct sites visited before escape is calculated for corrals of various sizes , shapes, and escape probabilities, and reduced to a common curve. Thi s fraction is also a measure of the probability that the diffusing spe cies will react with another species in the corral before escaping. Fi nally, the effect of the sampling interval on the measurement of the s hort-range diffusion coefficient is examined.