Membrane bending elasticity and its role for shape fluctuations and shape transformations of cells and vesicles

Abstract

Experimental evidence for the essential role of the curvature elasticity and the membrane-asymmetry-controlled spontaneous curvature for shape fluctuations and shape transitions of liposomes and erythrocytes is presented. Non-spherical flaccid vesicles can form a limited number of stable shapes such as discocytes (disc-shape), stomatocytes (cup-shape) two-vesicle states (small vesicle inside or outside large one), or beaded chains of vesicles. Transformations between these shapes are triggered by changes in the area difference between the inner and the outer monolayer in agreement with the bilayer-coupling model of Svetina and Zeks.Improved mechanical models of the red-blood-cell membrane have been prepared by incorporation of linearly polymerized macrolipids into vesicles, which then exhibit similar elastic constants as the RBC.The formation of two-vesicle states by changes in the global spontaneous curvature suggests that important cellular transport processes such as endocytosis and exocytosis may be triggered by biochemically induced expansions or compressions of one monolayer of the plasma membrane. The essential role of lateral redistribution processes for the final triggering of the vesicle detachment is stressed.