The proposed mechanism of stabilization of membrane nanotubes

by coupling of the local membrane shape and the lateral density of

the membrane constituents (nanodomains) is also one of the mech-

anisms relevant for the formation and stabilization of highly curved

spherical membrane buds. Figures 10.1 and 10.2 (Ha¨gerstrand et al.,

2006; Iglicˇ et al., 2007b; Laradji and Kumar, 2004; McMahon and

Gallop, 2005; Sens and Turner, 2004, 2006; Staneva et al., 2005;

Thiele et al., 1999) show the accumulation of isotropic membrane

nanodomains (having C1m = C2m), which favour high isotropic curvature, on a small bud. The fraction of the area covered by

nanodomains increases towards the tip of the bud. As the neck

becomes narrower, the distribution approaches a step function,

while the free energy of the nanodomains lowers the free energy of

the membrane.