Comparison of double layer potentials in lipid monolayers and lipid bilayer membranes

Abstract

It is shown that the Gouy-Chapman double layer analysis adequately describes the variation of the surface potential of monolayers of acidic natural lipids over a wide range of surface charge density and salt concentration. It is also shown that the potential which initially appears when an electrolyte gradient is rapidly imposed across a bilayer membrane is due to a difference in the double layer potentials on the two sides of the membrane. This conclusion follows from the fact that the observed bilayer potentials arise much more rapidly than can be accounted for by charge migration across the membrane and from the observation that the bilayer membrane concentration potentials, when measured immediately after establishment of a gradient, are equal to the surface potential change observed when the subphase concentration of a monolayer of the same lipid is changed by an amount equal to the gradient across the bilayer. The bilayer potential and monolayer potential changes, so measured, agree in a number of different electrolyte solutions over a wide range of electrolyte concentrations and surface charge densities. Because of this agreement and the applicability of the Gouy theory to monolayers, initial bilayer potentials may be calculated if the composition of the mixture used to form the membrane is known, provided that the pK's and areas of such components are available. In the absence of this information, membrane potentials may be calculated from electrophoretic data on the membrane lipid mixture; the conditions under which the latter approach is possible have been determined. The experimental results indicate that the composition of monolyers and bilayers spread from the same lipid mixture in decane are very similar, that the composition of the two types of film closely resembles the composition of the solution used to generate them, and that bilayer membranes are close-packed. The evidence further indicates that if any hydrocarbon solvent remains in these bilayers, it must be so situated that it contributes little, if anything, to the surface area. The steady state potential in the bilayer membrane system is frequently not identical with the initial potential which supports the hypothesis that in many cases only a fraction of the electrical conductance of unmodified membranes is caused by the ions which constitute the bulk electrolyte. An expression for the relationship between diffusion and double layer potentials has been derived which shows that, in the absence of any intrinsic selectivity of the hydrocarbon region of the membrane for hydrogen, hydroxyl, or impurity, the two potentials should be identical.

Effect of phloretin on the permeability of thin lipid membranes.

“…Since these decreases are seen in bilayers, it appears, contrary to popular belief (MacDonald and Bangham, 1972;Haydon and Myers, 1973) that monolayers at the air-water interface are not (in some respects) good models for half of a bilayer. 11 (It is possibly relevant that there appeared to be a slick on the water surface when films were spread from cholesterol-free, phospholipid-decane solutions but none when spread from cholesterol-containing, phospholipid-decane solutions.…”

Interaction of bilayers with basic polypeptides

“…Even though MacDonald and Bangham [12] considered the effect of the electrical double layer on the transmembrane potential, the interrelation between the ionic strength in the adjacent bulk phase, the double- layer potential and surface charge density were not considered in detail. We suggest that the interrelation between the structure of the membrane surface and the composition of the adjacent bulk phase is of general validity.…”

Electrogenesis from an ATPase-ATP-sodium pseudo pump

“…Although the sodium concentration was raised only 1% and the chloride concentration was unchanged, a 130 mV change appeared across the membrane with the side containing ATP becoming negative. The change in emf is too large to be due to a change in the Donnan equilibrium or to a change in the potential of the electrical double layer at the membrane surface (MacDonald & Bangham, 1972), and another explanation must be found.…”