Lipid redistribution due to a cell-cell fusion pore.

We consider the redistribution of lipids comprising the plasma membranes during cell-cell fusion, particularly due to the presence of a fusion pore. Assuming the membranes are of constant thickness, we find that the mole fraction of cholesterol increases in the directly apposed exoplasmic leaflets, and is decreased in the cytoplasmic leaflets. The redistribution of the phospholipids is obtained as well.

On the force between "rafts".

"Rafts" in the plasma membrane are nanoscopic domains rich in sphingolipids and cholesterol. Groups of them are thought to provide stable platforms for various proteins. How several rafts can form a larger stable platform has yet to be made clear.

Extent of raft composition in a model plasma membrane.

"Rafts" are nanometer-size inhomogeneities in the plasma membrane that, in the outer leaflet, are enriched in sphingomyelin and cholesterol. They are thought to provide a platform for proteins to carry out biological processes. Here, we employ a model asymmetric plasma membrane to address the question of the range of sphingomyelin and cholesterol compositions in which one would expect the formation of rafts.

A Theoretical Basis for Nanodomains.

We review the current theories of nanodomain, or "raft," formation. We emphasize that the idea that they are co-exisiting Lo and Ld phases is fraught with difficulties, as is the closely related idea that they are due to critical fluctuations. We then review an alternate theory that the plasma membrane is a two-dimensional microemulsion, and that the mechanism that drives to zero the line tension between Lo and Ld phases is the coupling of height and composition fluctuations.