title: Electrical characteristics in an excitable element of lipid membrane.
abstract: Electrical characteristics in a membrane constructed from a porous filter adsorbed with a lipid analogue, dioleoyl phosphate (DOPH), were investigated in a situation interposed between 100 mM NaCl + 3 mM CaCl2 and 100 mM KCl. Calcium ions affected significantly the membrane characteristics. The membrane potential was negative on the KCl side, which implies the higher permeability to K+ than Na+; this tendency was increased by a tiny amount of Ca2+. While the membrane showed a low electrical resistance of several k omega . cm2 under K+/Na+ gradient, it showed several M omega . cm2 by Ca2+. The surface structure of the membrane exhibited many voids in the low-resistance state, but the surface was covered by oil droplets in the high-resistance state. Oscillations of the membrane potential appeared spontaneously with application of the electrical current from the KCl side to the NaCl + CaCl2 side. The frequency was increased with the electrical current. All these results were explained comprehensively using an electrochemical kinetic model taking account of the Ca2+ binding effect, where DOPH assemblies make a phase transition between oil droplets due to Ca2+ and multi-bilayers with excess K+. The oscillation arises from coupling of the phase transition to accumulation and release of K+ or Ca2+. This membrane can be used as an excitable element regulated by Ca2+ in neuro-computer devices.
authors.affiliation: Department of Electronics, Faculty of Engineering, Kyushu University, Fukuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Toko
authors.forename: N
authors.initials: N
authors.lastname: Ozaki
authors.forename: S
authors.initials: S
authors.lastname: Iiyama
authors.forename: K
authors.initials: K
authors.lastname: Yamafuji
authors.forename: Y
authors.initials: Y
authors.lastname: Matsui
authors.forename: K
authors.initials: K
authors.lastname: Yamafuji
authors.forename: M
authors.initials: M
authors.lastname: Saito
authors.forename: M
authors.initials: M
authors.lastname: Kato
mesh_terms: D002118:Calcium / Q000737:chemistry; D004553:Electric Conductivity; D008563:Membrane Lipids; D008564:Membrane Potentials; D008855:Microscopy, Electron, Scanning; D010539:Permeability; D011188:Potassium / Q000737:chemistry; D012964:Sodium / Q000737:chemistry
chemical_list: D008563:Membrane Lipids; D012964:Sodium; D011188:Potassium; D002118:Calcium