The Diffusion of Ions from a Phospholipid Model Membrane System

Abstract

The recognition that biological cells exploit the surface-active properties of lipids to define anatomical membranes has, in recent years, encouraged many workers to develop and study model systems based upon the orientation of lipids at interfaces (Bangham 1963). A considerable advance was made when Mueller, Rudin, TiTien and Wescott (1964) and Haydon (quoted in Taylor 1963), simultaneously and independently reported a technique for the preparation of isolated bimolecular lipid membranes separating two aqueous compartments. Such preparations, although some­what fickle, have enabled a variety of physical parameters to be measured. The technique lends itself pre-eminently to electrical studies of a.c. and d.c. resistances and of capacitance (Thompson 1966, Hanai, Haydon and Taylor 1964). The major criticism of the technique, however, is that the precise composition of the “black” (bimolecular) membrane is in some doubt, since it has not been found possible to spread the membranes in the absence of a relatively large mole fraction of a “filler” hydrocarbon and of water insoluble solvents. Indeed, according to Clements and Wilson (1962), if as little as 1 % of the lipid mass in a membrane contains non-polar compounds, e.g. chloroform, the membrane may be considered to be in a fully anaesthetized state. A further difficulty is encountered when lipid mixtures analogous to those present in biological membranes fail to produce useful membranes.