Chaos in excitable lipid membranes

An artificial excitable lipid membrane, which is composed of a porous filter filled with lipids, exhibits self-sustained oscillation of the membrane potential by DC electric current imposed across the membrane. The system yielded various electric oscillatory responses to sinusoidal AC electric currents superimposed on the DC current. At adequate frequency and amplitude of the sinusoidal stimulation, the oscillation was entrained (or synchronized) to the stimulation; the oscillation was desynchronized when the parameter (frequency or amplitude) was deviated to some extent from the initial value. Aperiodic oscillations appeared for parameter values located between entrained regions. Detailed analyses revealed that the aperiodic oscillations were chaotic, which was first shown quantitatively in artificial membrane systems.