Determination of the electroporation onset of bilayer lipid membranes as a novel approach to establish ternary phase diagrams: example of the L-α-PC/SM/cholesterol system

The lipid matrix of cell membranes contains phospholipids belonging to two main classes, glycero- and sphingolipids, as well as cholesterol. This matrix can exist in different phases, liquid disordered (l(d)), liquid ordered (l(o)) and possibly solid (s(o)), or even a combination of these. The precise phase composition of a membrane depends on its molecular content and more specifically on the presence and amount of cholesterol. This in turn dictates the membrane properties. In this work, the resistance of membranes to the process of electroporation is studied and related to the membrane phase composition. Specifically, the threshold voltage for electroporation is measured (V-th) when DC pulses with increasing amplitude are applied to membranes prepared from various mixtures of a glycerolipid (Heart PC (L-alpha-PC)), a sphingolipid (Egg SM (SM)) and cholesterol (Ch), introduced in various ratios. Binary mixtures (L-alpha-PC/Ch, L-alpha-PC/SM, SM/Ch) and L-alpha-PC/SM/Ch ternary mixtures are successively employed. For all binary and ternary systems, dramatic changes in V-th are measured as a function of the membrane molecular composition, and the variation patterns of V-th are successfully correlated with the membrane phase composition. Interestingly, the measure of the electroporation onset can be employed as a novel methodology to establish ternary phase diagrams, and this is illustrated with the L-alpha-PC/SM/cholesterol ternary system.