The Diffusion of Ions from a Phospholipid Model Membrane System
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 (Bangh
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Membrane Models Invited Papers
The Diffusion of Ions from a Phospholipid Model Membrane System By
A. D. Bangham, M. M. Standish!, J. C. Watkins 2, and G. Weissmann 3 Ag~icU'lturall
Research Council, Institute of Animal Physiology, Habraham, Cambridge, England With 1 Figure
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 hased upon the orientation of lipids at interfaces (B a n,g ham .1963). A considerable advance was made when Mueller, R'll di n, T i Ti e n ·and Wes co t t (1%4) ,and Haydon (quoted in T a y lor 1%3), simultaneously and independently reported a technique for the preparation of isolated bimolecular lipid membranes separating two aqueous compartments. Such preparations, although somewhat fickle, haveenahled 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 (T hom p so n1966, Han a i, Haydon and T a y lor 1%4). The major criticism of the technique, however, is that the precise composition of the "black" {himolecular) membrane is in some doubt, since it has not been found possible tD spread the membranes in the absence of a relatively large mole fraction of a "filler" hydrocarbon and of water lillJsolruble solvents. Indeed, accoooing to C Ie m·e ntIS land W:i 1 son (1%2), 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 tD those present in biological membranes fail to produce useful membranes. The liquid crystal (smectic mesophase) is a preferred phase structure of many biological lipids in the presence of water or salt solutions (see review Visiting Scientist from Unilever, Colworth HQuse, Bedford. V,isit.ing Scientist from Department of Physiology, Australian National Univers.ity, Canberra. 3 Visiting Scientist from New York University School of Medicine, New York. 1
2
L. Bolis et al. (eds.), Symposium on Biophysics and Physiology of Biological Transport © Springer-Verlag/Wien 1967
184
A. D. Bangham, M. M. Standish,
J.
C. Watkins, and G. Weissmann
by D e r vic h ian 19(4). It may be ascribed to the nature and heterogeneity of the hydrocarhon moieties and to the possession by the lipids of either polar, tianogenic or both typ·es of hewd gl'OllJp. The preci1se geometry of the ,structures deperuds upon the rela,tive concentration of the ·two pl'lincipal component,s (lipIDd and wata-), rthe temperatul'e, the composition of ,the lip,i,d and the ,saH concentrataon of the aqU'ooUIS phase (Bangiham 1964, Ha ydon and Taylor 1963, Lawrence 1961, Luzzati and Husson 19(6). Over a wide range of such variables, however, the commonest phase structure appears to be that of a layer lattice giving rise to spherulites and myelins, both composite structures consisting of
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