2013
Volume 13, Number 1, pp. 5–8
Interactions of phloretin and quercetin with lipid bilayers studied by a simplified method of second harmonics of the membrane current
P.A. Grigoriev
Institute of Cell Biophysics, Russian Academy of Sciences, 142290 Puschino, Moscow region, Russia
We studied the interaction of the flavonoids phloretin and quercetin with planar lipid bilayers using a very simple setup for the method of higher harmonics of membrane current. It is known that the second harmonic appears when a.c. and d.c. voltages are simultaneously applied to the membrane and that the amplitude of the signal is proportional to the intensity of the field inside the hydrophobic region of the bilayer. The position of the minimum of the amplitude is shifted along the horizontal axis (external voltage) d.c. depending on the degree of asymmetry in the surface potentials of the bilayer. Adsorption of phloretin or quercetin at one of the bilayer interfaces shifted the minima in the positive direction, meaning that either the positive potential of that interface is reduced or the potential of the opposite interface is increased due to flavonoid adsorption. In addition we have shown that these flavonoids diminished valinomycin- or carbonyl cyanide m-chlorophenylhydrazone (FCCP)-induced conductance of the membrane, which allowed us to propose the second of the two alternative molecular mechanisms of flavonoid activity; that is, the potential of the opposite interface is increased. The observed amplitudes of the effects were correlated with the dipole moments of the flavonoids.
Keywords: flavonoids, lipid bilayer, second harmonic