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Recently, we showed that the effect of dipole modifiers (flavonoids and styrylpyridinium dyes) on the conductance of single amphotericin B (AmB) channels in sterol-containing lipid bilayers primarily resulted from changes in the membrane dipole potential. The present study examines the effect of dipole modifiers on the AmB multi-channel activity. The addition of phloretin to cholesterol-containing membranes leads to a significant increase in the steady-state AmB-induced transmembrane current. Quercetin significantly decreases and RH 421 increases the current through ergosterol-containing bilayers. Other tested flavonoids and styrylpyridinium dyes do not affect the channel-forming activity of AmB independently on the sterol composition of the bilayers. The effects obtained in these trials may instead be attributed to the direct interaction of dipole modifiers with AmB/sterol complexes and not to the effect of dipole potential changes. The presence of double bonds in the Δ7 and Δ22 positions of sterol molecules, the number of conjugated double bonds and amino sugar residues in polyene molecules, and the conformation and adsorption plane of dipole modifiers are important factors impacting this interaction. [ABSTRACT FROM AUTHOR]

The effects of dipole modifiers and their structural analogs on the single channel activity of amphotericin B in sterolcontaining planar phosphocholine membranes are studied. It is shown that the addition of phloretin in solutions bathing membranes containing cholesterol or ergosterol decreases the conductance of single amphotericin B channels. Quercetin decreases the channel conductance in cholesterol-containing bilayers while it does not affect the channel conductance in ergosterol-containing membranes. It is demonstrated that the insertion of styryl dyes, such as RH 421, RH 237 or RH 160, in bilayers with either cholesterol or ergosterol leads to the increase of the current amplitude of amphotericin B pores. Introduction of 5α-androstan-3β-ol into a membrane-forming solution increases the amphotericin B channel conductance in a concentration-dependent manner. All the effects are likely to be attributed to the influence of the membrane dipole potential on the conductance of single amphotericin B channels. However, specific interactions of some dipole modifiers with polyene-sterol complexes might also contribute to the activity of single amphotericin B pores. It has been shown that the channel dwell time increases with increasing sterol concentration, and it is higher for cholesterol-containing membranes than for bilayers including ergosterol, 6-ketocholestanol, 7-ketocholestanol or 5α-androstan-3β-ol. These findings suggest that the processes of association/dissociation of channel forming molecules depend on the membrane fluidity. [ABSTRACT FROM AUTHOR]

While it is accepted that biomembrane asymmetry is generated by proteins and phospholipids distribution, little is known about how electric changes manifested in a monolayer influence functional properties of proteins localized on the opposite leaflet. Herein we used single-molecule electrophysiology and investigated how asymmetric changes in the electrostatics of an artificial lipid membrane monolayer, generated oppositely from where alamethicin - a model voltage-gated ion channel - was added, altered peptide activity. We found that phlorizin, a membrane dipole potential lowering amphiphile, augmented alamethicin activity and transport features, whereas the opposite occurred with RH-421, which enhances the monolayer dipole potential. Further, the monolayer surface potential was decreased via adsorption of sodium dodecyl sulfate, and demonstrated that vectorial modification of it also affected the alamethicin activity in a predictive manner. A new paradigm is suggested according to which asymmetric changes in the monolayer dipole and surface potential extend their effects spatially by altering the intramembrane potential, whose gradient is sensed by distantly located peptides. [ABSTRACT FROM AUTHOR]