The dipole-modifying effect of styrylpyridinium dyes and flavonoids on model membranes of different lipid compositions

Abstract

Changes in dipole potential of lipid bilayers ϕd mimicking cell membranes induced by the adsorption of low-molecular-weight amphiphiles, flavonoids (phloretin and quercetin), and styrylpyridinium dyes (RH 421 and RH 237) were measured. A method based on the determination of ionophore-induced transmembrane current was used to evaluate changes in ϕd after modifier addition. The characteristic parameters of the Langmuir adsorption isotherm and the greatest changes in ϕd at an infinitely large concentration of flavonoid and its desorption constant, which reflects the affinity of the flavonoid to the lipid phase, were determined. The slopes of linear dependences of ϕd increasing on the concentration of the styrylpiridinium dyes in membrane-bathing solution were defined. It was found that the dipole-modifying effect of phloretin depends on the charge of the lipids forming the membranes, while the ability of quercetin to reduce ϕd is determined by the initial hydration of the bilayer. The results indicate that there are different mechanisms of the decrease in ϕd upon the adsorption of the tested flavonoids. It was shown that the changes in ϕd at the incorporation of styrylpyridinium dyes into bilayers are determined by the interaction of modifiers with membrane components.