Temporal Analysis of Active and Passive Transport in Living Cells

The cellular cytoskeleton is a fascinating active network, in which Brownian motion is intercepted by distinct phases of active transport. We present a time-resolved statistical analysis dissecting phases of directed motion out of otherwise diffusive motion of tracer particles in living cells. The distribution of active lifetimes is found to decay exponentially with a characteristic time tau(A)=0.65 s. The velocity distribution of active events exhibits several peaks, in agreement with a discrete number of motor proteins acting collectively.