Fences catch free-ranging lipids

Lipids diffuse in a cell membrane at least fivefold more slowly than they do in an artificial lipid bilayer, a discrepancy that has puzzled cell biologists for more than two decades. Now, on page 1071, Fujiwara et al. suggest an explanation: the cell surface is crisscrossed with picket fences made of immobile transmembrane proteins.

Until now, single-particle tracking (SPT) has been too slow to provide a high-resolution view of lipid diffusion. In an impressive technical achievement, the authors developed a SPT technique with 25-μs resolution, and then used it to follow the diffusion of a nonraft lipid in a cell membrane.

The lipid molecule was confined within a defined compartment for an average of 11 ms before hopping to an adjacent compartment on the cell membrane. Within the compartment, diffusion was about as fast as in artificial membranes,...