A MODEL FOR SELF-SUSTAINED POTENTIAL OSCILLATION OF LIPID BILAYER-MEMBRANES INDUCED BY THE GEL LIQUID-CRYSTAL PHASE-TRANSITIONS

To clarify the mechanism of self-sustained oscillation of the electric potential between the two solutions divided by a lipid bilayer membra ne, a microscopic model of the membrane system is presented. It is ass umed, on the basis of the observed results (Yoshikawa, K., T. Omachi, T. Ishii, Y. Kuroda, and K. liyama. 1985. Biochem. Biophys. Res. Commu n. 133:740-744; Ishii, T., Y. Kuroda, T. Omochi, and K. Yoshikawa. 198 6. Langmuir. 2:319-321; Toko, K., N. Nagashima, S. liyama, K. Yamafuji , and T. Kunitake. Chem. Lett. 1986:1375-1378), that the gel-liquid cr ystal phase transition of the membrane drives the potential oscillatio n. It is studied, by using the model, how and under what condition the repetitive phase transition may occur and induce the potential oscill ation. The transitions are driven by the repetitive adsorption and des orption of proton by the membrane surface, actions that are induced by the periodic reversal of the direction of protonic current. The essen tial conditions for the periodic reversal are (a) at least one kind of cations such as Na+ or K+ are included in the system except for proto n, and the variation of their permeability across the membrane due to the phase transition is noticeably larger than that of proton permeabi lity; and (b) the phase transition has a hysteresis. When these condit ions are fulfilled, the self-sustained potential oscillation may be br ought about by adjusting temperature, pH, and the cation concentration in the solutions on both sides of the membrane. Application of electr ic current across the membrane also induces or modifies the potential oscillation. Periodic, quasiperiodic, and chaotic oscillations appear especially, depending on the value of frequency of the applied alterna ting current.