ABSTRACT
A common structural motif of all biological membranes is the fluid lipid bilayer as illustrated. The lipid bilayer is the core of the membrane, and it provides the cell with an appropriate permeability barrier and hence supports a distinction between the inside and outside of the cell. This chapter summarizes some of the techniques which have provided information on bilayer permeability in the transition region with a view to evaluating the accuracy and reliability of the experimental data. It describes results obtained from computer simulations of the ten-state model for bilayer fluctuations, macroscopically and microscopically, and how these fluctuations can be used in a model of bilayer permeability. Measurements of mechanical properties of bilayers often involve permeation of water, ions or specific dyes. Such experiments, as well as direct studies of permeability properties of bilayers, are in general delicate to perform.
