Impedance Analysis of Lipid Domains in Phosphatidylcholine Bilayer Membranes Containing Ergosterol

The effect of ergosterol on the electrochemical features of the phosphatidylcholine bilayer membrane was investigated by impedance spectroscopy. The experimental impedance values obtained in the presence of different amounts of ergosterol showed evidence of domain structures within the bilayer containing <0.06 molar fraction of ergosterol. Based on derived mathematical equations, the surface area of phospholipid/ergosterol domain was calculated; it amounts to 262 Å2. This value is consistent, taking into consideration the presented measurements as well as ordering and condensation effects of ergosterol, with a stoichiometry of such a domain equal to 3:1. The result of the investigation is the proposal of a new and simple method for the determination of the surface area and description stoichiometry of domains formed in any two-component system.