Sucrose solutions alter the electric capacitance and dielectric permittivity of lipid bilayers

Understanding sugar-membrane interactions is of fundamental and technological relevance considering the role of sugars in drought-protection mechanisms of plants as well as the cryo-and bio-preserving effect of carbohydrates in many industrial and medical applications. In this work, we investigated the effect of sucrose on the electrical properties of membranes. In particular, we measured the specific capacitance of palmitoyl-oleoyl phosphatidylcholine membranes in aqueous solutions of sodium chloride. Different concentrations of sucrose were examined. The capacitance was assessed from the frequency-dependent deformation of giant unilamellar lipid vesicles in alternating electric field. Our measurements on giant vesicles in sugar-free aqueous solutions yield lower specific capacitance compared to values obtained for suspended and supported bilayers. This might be a result of the higher membrane tension in the latter systems, which is coupled to smaller thickness of the bilayer. We also report an increase of the bilayer capacitance upon increasing the sugar content in water. This finding is consistent with the sugar-induced thinning of membranes reported in the literature. However, the thinning is not sufficient to explain the observed capacitance increase with rising sugar concentration. We interpret the trend as resulting from an increase in the membrane dielectric permittivity.