Non-isothermal potential of phospholipid bilayer films. Influence of cholesterol and macrocyclic carrier effects.

The effect of cholesterol on the ion selective behavior of phoshpolipid (phosphatidylcholine or phosphatidylethanolamine) bilayer films is studied through the measurement of the membrane non-isothermal potential. It is shown how the mixed phosphatidylcholine-cholesterol membrane can be either cation of anion permselective according to the film composition (cationic behavior is met in the 0--10% cholesterol composition range while anionic selectivity appears in the 20--50% range). On the contrary, mixed phosphatidylethanolamine-cholesterol membranes show the absence of ionic selectivity already met with pure phosphatidylethanolamine films.

Non-isothermal potential of phospholipid bilayer films.

The thermal electrical potential generated in isochemical conditions by a temperature gradient at the two sides of lipid bilayer leaflets is measured. The experimental results agree rather well with the theoretical predictions. The cephaline (from sheep brain) bilayer behaves like a film with zero charge while the phosphatidylcholine (from egg yolk) film performs like a charged membrane.

Liquid membrane potential in nonisothermal systems.

Electrical membrane potential equations for liquid ion exchange membranes, characterized by the presence of uncharged associated species and by exclusion of co-ions (no electrolyte uptake) have been derived. The irreversible thermodynamic theories already developed for solid membranes with fixed charged site density have been extended to include the different physicochemical aspects of the liquid membranes. To this purpose the dissipation function has been written with reference to the fluxes of all the species present in the membrane.