Determination of reflection coefficients of liposomes for some non-electrolytes by osmotic pressure measurement.
The reflection coefficients of bilayer lipid vesicles (liposomes) of various compositions have been determined for a number of non-electrolytes. The solutes were the same and the method of measurement was essentially the same as those which have been used to estimate an equivalent pore radius for erythrocytes. The method involves matching the osmotic pressure of solutions of a permeant test solute with that of a known inpermeant solute. Reflection coefficients for cholesterol-containing liposomes and those of erythrocytes are, when account is taken of those solutes known to permeate the erythrocyte by specialized pathways, not greatly different. Lipid bilayers can thus account for most of the permeability characteristics of the cell originally interpreted as due to aqueous pores. Reflection coefficients are significantly higher for egg phosphatidylcholine membranes that contain cholesterol than those which do not. There is a strong correlation between relative permeabilities derived from reflection coefficients and oil-water partition coefficients. There is also good agreement between these permeabilities and permeabilities measured by others, which exhibit an inverse dependence on molecular size. It is suggested that this tendency of membranes to pass small molecules more readily than large molecules, other properties being equal, is a consequence of the surface pressure of the constituent monolayers of the membrane.
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, IL 60201.
R C
RC
MacDonald
R J
RJ
Weingarten
D004058:Diffusion; D008051:Lipid Bilayers; D008081:Liposomes; D009997:Osmotic Pressure; D010539:Permeability; D012997:Solvents
D008051:Lipid Bilayers; D008081:Liposomes; D012997:Solvents