Effects of Flavonoids on Dipole Potential of Sterol-Containing Membranes

Abstract

Flavonoids are hydroxylated polyphenoles from plants which show antioxidant, antiinflammatory, antitumoral, and other therapeutic properties. It is known that flavonoids are membrane-active agents and some of them are able to influence on the membrane structural and dynamic properties. The role of the membrane dipole potential (Vd) is a particular interest due to a powerful impact of Vd on the membrane permeability and lipid-protein interactions. It is known that the flavonoids, phloretin and phloridzin, significantly reduce Vd of phospholipid bilayers [Andersen et al., 1976], but their effects on sterol-containing bilayers are unknown. We estimated the changes of dipole potential (ΔVd) of phosphocholine bilayers containing 33 mol % of cholesterol (the major membrane sterol of mammalian cells) or ergosterol (the major membrane sterol of fungi) after addition into bilayer bathing solution (0.1M KCl pH7.4) of phloretin, phloridzin, genistein, quercetin and biochanin A up to 20 μM. The corresponding calculations were performed assuming that the membrane K+-nonactin steady-state conductance is related to Vd by the Boltzmann distribution [Andersen et al., 1976]. We found that in the presence of phloretin ΔVd of phosphocholine membranes was equal to −130 ± 10 mV, of phosphocholine:cholesterol bilayers is −75 ± 10 mV, and of phosphocholine:ergosterol membranes is −150 ± 10 mV. In contrast to phloretin introduction of phloridzin, genistein, quercetin and biochanin A changes Vd of bilayers of above composition in a similar manner. The average values of ΔVd were −55 ± 10 mV, −40 ± 10 mV, −110 ± 10 mV, and −80 ± 10 mV, respectively. The study was supported in part by RFBR (#09-04-00883), SS-3796.2010.4 and the Program of Presidium of the RAS «Molecular and Cell Biology».