Fig. 2.

Schematic representation of surface pressure, lipid asymmetry, membrane budding and endocytosis in membranes. a Sketch representing the profile of surface pressure within the membrane. b Schematic relation between fluid phase endocytosis and the differential packing of lipids. The vesicle radius is, geometrically speaking, inversely proportional to the lipid number asymmetry between leaflets [21]. c The phospholipid number asymmetry maintained by the aminophospholipid translocase leads to membrane bending and vesiculation. Note that the membrane recycling that occurs in cells (right panel), with a size similar to endocytic vesicles, allows the maintenance of the lipid asymmetry. Given the lipid asymmetry in membranes it is supposed that the surface pressure is constant in either leaflet [21]