Electrical characteristics in an excitable element of lipid membrane.
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.
Toko
K
K
Department of Electronics, Faculty of Engineering, Kyushu University, Fukuoka, Japan.
Ozaki
N
N
Iiyama
S
S
Yamafuji
K
K
Matsui
Y
Y
Yamafuji
K
K
Saito
M
M
Kato
M
M
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
D008563:Membrane Lipids; D012964:Sodium; D011188:Potassium; D002118:Calcium