Plasma membranes: does one model fit all?

Biological membranes consist of a lipid bilayer with a highly asymmetric distribution of lipids in the two leaflets. This asymmetry is maintained by enzymes whose activities depend on cytosolic ATP and Ca²⁺ concentrations. Recently, a new model for plasma membranes (PMs) was introduced. It is based on studies with human erythrocytes and suggests that there is a 50% overabundance of lipids with two hydrophobic chains in the cytosolic leaflet, compensated by the presence of three times more cholesterol in the outer leaflet. In this opinion article, we discuss the large differences in lipid composition between erythrocytes and other cell types, the assumptions used to reach the new membrane model, and whether this model would fit PMs of other cell types.