Experimental and Theoretical Data on Excitable Artificial Lipidic Membranes

A drop of a drying oil, i.e. an unsaturated glyceride:(linseed oil), spreads upon an oxidizing solution (MnO4K 0.1%) and forms, after a few hours, a thin, flexible floating membrane, showing bright interference colors; this indicates a thickness which can fall below 1 t~ (Monnier and Monnier, 1964). This membrane can be floated on a saline solution and can support a drop of another solution. Thus it separates two distinct aqueous phases into each of which an Ag-AgCI-KCI electrode can be inserted. This constitutes a model of the cell membrane which exhibits curious analogies: excellent cation selectivity; hi-ionic potentials indicating different permeability toward the various cations (permeability for K + markedly greater than that for Na+); nonlinear current-voltage relation; excitability showing "responses" characterized by sudden and temporary increases of conductance; frequency of responses increasing with the current; impedance locus of the resting membrane represented by an almost perfect Cole's half-circle centered on the resistance axis (this allows the membrane to be described formally as a resistance and a capacity in parallel); charging time of the same order as that of some living excitable membranes (Monnier et al., 1965 a, b). Part of the above features can be attributed to anionic fixed charges induced in the membrane by its formative process, oxidative polymerization. Recent work has confirmed and extended these results.