Cylindrical equilibrium shapes of fluid membranes

Within the framework of the well-known curvature models, a fluid lipid bilayer membrane is regarded as a surface embedded in the three-dimensional Euclidean space whose equilibrium shapes are described in terms of its mean and Gaussian curvatures by the so-called membrane shape equation. In the present paper, all solutions to this equation determining cylindrical membrane shapes are found and presented, together with the expressions for the corresponding position vectors, in explicit analytic form. The necessary and sufficient conditions for such a surface to be closed are derived and several sufficient conditions for its directrix to be simple or self-intersecting are given.Comment: 17 pages, 4 figures. Published in J. Phys. A: Math. Theore

Plasma membrane-associated proteins are clustered into islands attached to the cytoskeleton

Although much evidence suggests that the plasma membrane of eukaryotic cells is not homogenous, the precise architecture of this important structure has not been clear. Here we use transmission electron microscopy of plasma membrane sheets and specific probes to show that most or all plasma membrane-associated proteins are clustered in cholesterol-enriched domains (“islands”) that are separated by “protein-free” and cholesterol-low membrane. These islands are further divided into subregions, as shown by the localization of “raft” and “non-raft” markers to specific areas. Abundant actin staining and inhibitor studies show that these structures are connected to the cytoskeleton and at least partially depend on it for their formation and/or maintenance