Influence of the Surface Charge Distribution and Water Layers on the Permeability Properties of Lipid Bilayers
The barrier properties of a biological membrane are mainly due to the stabilization of the lipid components in a bilayer conformation. The overall permeation phenomena for polar molecules involves the interaction of the permeant at the membrane/solution interface and its penetration into the hydrocarbon core. The hydration shell of the phospholipid molecules contributes to the permeability barrier as determined by equilibrium dialysis experiments. In this paper, it is shown that the adsorption of Ca on the inner and the outer interfaces of a sonicated vesicle bilayer of egg phosphatidylcholine can affect the barrier properties to non-electrolytes. In addition, P nuclear magnetic resonance shows that the adsorption of Ca+2 on the inner interface of the vesicle promotes a conformational change of the bilayer affecting the adsorptive properties of the outer interface.
This transbilayer effect is related to the changes in the order parameter of the hydrocarbon chains of the bilayer as demonstrated by fluoro-metric experiments. A semi-quantitative analysis of the conformational change and the stoichiometry of the Ca+2 adsorption is discussed.
KeywordsLipid Bilayer Barrier Property Phosphatidic Acid Polar Head Group Outer Solution
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