Dioleyl Phosphate Research Articles

合成脂質膜における味覚応答

The effect of taste stimulants on a DOPH (dioleyl phosphate) Millipore membrane was investigated as a model system of taste reception. Quinine, HCl, NaCl and sucrose were chosen as bitter, sour, salty and sweet substances, respectively. From the measurements of membrane potential and membrane resistance, it is conceivable that quinine, HCl and NaCl affect a phase boundary potential while sucrose affects a diffusion potential. Dynamic profiles of membrane potential also suggested that HCl and NaCl acted at the surface of membrane, but quinine and sucrose penetrated into the membrane. The intensity of their action on an electric potential was associated qualitatively with the threshold values of taste reception in man. Most of the results found in this model membrane may be realized for a living system. On the difference of taste quality between sour and salty substances, some discussions were added.

電位・電流固定法によるミリポアＤＯＰＨ膜の電流‐電圧特性

The Millipore DOPH model membrane is composed of a Millipore filter whose pores are filled with a lipid analogue, dioleylphosphate (DOPH). The electric resistance of the Millipore DOPH membrane is increased in the mixed salt solution such as KCl and CaCl2, and it oscillates rhythmically under which a current and a pressure stimulus are applied simultaneously. This paper showed electric current (I) -voltage (V) characteristics to discuss the plausible mechanism of the resistance oscillation, because I-V characteristics were one of important properties to described the mechanism of an electric oscillation, and these had not been examined in the Millipore DOPH membrane. The current and voltage responses were observed by using the current or voltage clamp circuits which were made by us. The current or the voltage increased linearly till 0.15 μA or 400mV, but above its oscillatory changes appeared. These meaned that it was difficult to discuss the oscillation mechanism with only I-V characteristics as compared with living cell membranes. The Millipore DOPH membrane consists of many small membranes such as oil droplets, spherical micelles and multilayers formed in filter pores. The oscillations observed under clamps come from this complex structure. From I-V characteristics, however, the structure of the Millipore DOPH membrane could be demonstrated by the simplest model connected with capillaries. Using the capillary model it could be easy illustrated that the sustained oscillation was caused by the conformational change of the small membrane in one capillary.

ミリポアＤＯＰＨ膜のＣａ｀２＋´イオンによる表面構造変化

The surface structure of a model membrane composed of a Millipore filter and a synthetic lipid analogue, i.e., dioleylphosphate (DOPH), immersed in KC1 solution changes when CaCl2 concentration reaches a critical value. By the stereoscopic microscope mounted a photomultiplier on the eyepiece the structure change can be measured quantitatively as an intensity change of reflected light of the membrane surface. Calcium ions decreased finally the intensity to more or less 50% as compared with the original hydrophilic state whose solution was only KC1. The structure changes were observed with various adsorbed densities of DOPH, solution temperatures and pH. The degree of structure change was dependent on these conditions.The structure observation can also be used to detect the CaCl2 concentration in KCl solution. Since the critical CaCl2 concentration shifts widely with various densities of DOPH adsorbed in Millipore filter, the detection range was from 0.1 to 50mM CaCl2.

Effect of Bitter Substances on a Model Membrane System of Taste Reception

The effect of bitter substances on the self-sustained electric oscillation of a DOPH (dioleyl phosphate)-Millipore membrane was investigated as a model system of taste reception. Caffeine and theobromine, having higher taste thresholds, had slight effect, but quinine, strychnine and nicotine, exhibiting strong bitterness, increased the frequency of the oscillation. The mode of action of bitter substances on the DOPH-Millipore membrane in the non-oscillatory state suggested that they cause the receptor potential by a change in the phase boundary potential. The intensity of action on the electric potential was associated with the threshold values of bitterness.

Self-sustained oscillations of electric potential in a model membrane

A model membrane constructed from a Millipore filter, whose pores are filled with dioleyl phosphate molecules, exhibits a self-oscillation of the electric potential with a period of about a few seconds in the presence of a salt-concentration difference, pressure difference and/or electric current across the filter. In this paper, the effects of chemicals such as KCl, CaCl 2, pH and sucrose on the self-oscillation are investigated experimentally. These chemical substances are shown to alter the characteristic properties as the frequency of oscillation. Theoretical consideration of electrochemical interaction between these substances and DOPH molecules gives a fairly good explanation of the observed results.

構造変化を伴うミリポアＤＯＰＨ膜の膜電気抵抗振動

A Millipore DOPH model membrane is composed of a Millipore filter whose pores are filled with dioleylphosphate (DOPH);and increases its electric resistance by a factor of 104 when Ca2+ ions are combined with it. The concentration of CaCl2 which increases the membrane resistance depends on the density of DOPH adsorbed in the filter and the initial KCl concentration. The surface structure of the membrane changes at the same time when the membrane resistance increases. By the stereoscopic microscope mounted a photomultiplier on the eyepiece the structure change can be detected quantitatively as an intensity change of reflected light, i. e.; Ca2+ ions decrease the intensity to 50% as compared with the original hydrophilic state.The membrane resistance which became higher with Ca2++ ions oscillates while the current and pressure stimuli are applied to the membrane. The frequency is dependent of these stimuli. These stimuli change the membrane surface structure to make locally the hydrophilic areas. It is conceivable that the structure changes are caused by replacing Ca2+ ions with K+ ions in the hydrophilic groups of DOPH molecules.

Effect of bitter substances on a model membrane system of taste reception.

The effect of bitter substances on the self-sustained electric oscillation of a DOPH (dioleyl phosphate)-Millipore membrane was investigated as a model system of taste reception. Caffeine and theobromine, having higher taste thresholds, had slight effect, but quinine, strychnine and nicotine, exhibiting strong bitterness, increased the frequency of the oscillation. The mode of action of bitter substances on the DOPH-Millipore membrane in the non-oscillatory state suggested that they cause the receptor potential by a change in the phase boundary potential. The intensity of action on the electric potential was associated with the threshold values of bitterness.

Current-voltage characteristics and self-sustained oscillations in dioleyl phosphate-millipore membranes

For an artificial membrane prepared by infiltrating dioleyl phosphate (DOPH) into pores of a Millipore filter, we propose a theoretical model for explaining observed data on electric behavior, such as d.c. current-voltage characteristics and self-sustained oscillations of the electric potential. The model consists of a simple electric circuit composed of electric resistances and capacitances as given functions of internal variables which represent conformational states of DOPH molecules and salt concentration inside the pore concerned. The kinetic equations for these variables are the same as those presented previously for describing a phase transition of DOPH. except for a slight modification taking account of effects of salt accumulation inside the pore. The present theory can describe well the I-V hysteresis and various features of spike-like oscillations with long periods of up to a few hours in the absence of external force and also short-period oscillations with periods of the order of 1 s under pressure difference.

Self-Sustained Oscillations of Membrane Potential in DOPH-Millipore Membranes

Self-sustained oscillations of membrane potential in an artificial model membrane, where dioleyl phosphate (DOPH) is infiltrated into pores of a Millipore filter, are investigated both experimentally and theoretically. Spike-like self-oscillations with an extremely long period of about one hour were observed for membranes with large adsorbed amounts of DOPH in the absence of external forces such as electric current and pressure gradient. On the basis of a previously-presented model that DOPH molecules make transitions among three phases composed of oil droplets, spherical micelles and multi- or bilayer leaflets, the occurrence of self-oscillations is explained well by taking account of an accumulation and a release of salt in a pore of the filter.

Dynamic Aspect of a Phase Transition in DOPH-Millipore Membranes

For an artificial membrane in which dioleyl phosphate (DOPH) is infiltrated into pores of Millipore filter, a relaxation of electric caracitance of the membrane in a solution was investigated after an abrupt change of salt concentration. Relaxation curves of sigmoid types were observed after an increase of salt concentration, while the curves were of exponential types after a decrease. These facts suggest us that hysteresis loops of electric capacitance or this membrane observed for a cyclic variation of salt concentration belong to a different type from the usual ones originating from the first-order phase transition. It is shown that these electric characteristics of the membranes can be explained well on the basis of a model that dioleyl phosphate molecules make transitions among three phases composed of droplets, spherical micells and multi- or bilayer leaflets.

The adsorption of lysine vasopressin at ionized interfaces

It has been shown by surface potential measurements that lysine vasopressin and oxytocin may be bound by ionic surfaces to very varied extents. To dodecyl sulphate and phosphatidylserine monolayers the binding is very strong and is comparable to that for biological receptors such as those in toad bladder. For dioleyl phosphate and the carboxyl group of the polypeptide alamethicin, the binding is rather weaker while, for the zwitterionic lipids phosphatidylcholine and phosphatidylethanolamine, and for the erythrocyte surface, which contains two varieties of carboxylic acid group, no interaction seems to take place. In no system does the lysyl amino group of the vasopressin appear necessary for adsorption and, in the dodecyl sulphate monolayers, the interaction is strong even when the ionization of the terminal α-amino group is suppressed.

Ultra-thin Layer of Lipids in Polymer Film and Its Electric Properties. New Sorption Method to Prepare a Model Biomembrane System

Abstract The ultra-thin layer of glycerol α-cis-9-octadecenate (glycerol α-monooleate:GMO) could be formed by impregnating nitrocellulose (NC) film with GMO and by then filling microscopically the interstices of the network structure of NC with microdrops of GMO. The dielectric dispersion characteristic of this film was found to be similar to that observed for bimolecular films. In a concentrated KCl solution (100 mM), however, an anomalous dielectric dispersion phenomenon was observed below 10 kHz. The low-frequency dispersion was attributed to surface conductance along the planes of contact between the GMO microdrops and the NC network. The ultra-thin film of di(cis-9-octadecenyl)phosphate (dioleyl phosphate: DOPH) could also be formed by this method. When a constant DC voltage (50 mV) was applied across the film in a 20 mM KCl solution, the electric current through the whole system changed periodically.

Transport phenomena in a model membrane accompanying a conformational change: Membrane potential and ion permeability

Membrane potential Δϕm ion permeabilityP and d-c conductanceGp0 of a model membrane composed of a filter paper and a synthetic lipid analogue, i.e. dioleylphosphate (DOPH), were observed in various concentrations of 1∶1 type electrolyte solution. With successive increases of salt concentration in the external solution, Δϕm,P andGp0 changed their values rather discontinuously at a certain critical value of the concentrationct. When the concentration was decreased successively, the values of Δϕm,P andGp0 were returned to the original levels at a concentration much lower thanct. Thus, the transport phenomena observed across the membrane showed an appreciable hysteresis loop.

Studies of Electric Capacitance of Membranes: I. A Model Membrane Composed of a Filter Paper and a Lipid Analogue

A hydrophobic filter paper of a given pore size containing a synthetic lipid, i.e. dioleyl phosphate, was interposed between aqueous electrolyte solutions having the same chemical composition and temperature. The electric capacitance and conductance of the membrane immersed in various concentrations of KCl were measured in the frequency range from 20 to 3 x 10(6) cycle/sec. The observed capacitance and conductance were found to be strongly dependent on the applied frequency. A theory is proposed to account for this dispersion of impedance observed in the present membrane-electrolyte system. The dispersion is attributed to the formation of bilayer membranes of the lipid inside the filter paper. The effects of the salt concentration, the adsorbed quantity of the lipid, and the pore size of the filter paper on the capacitance and conductance of the membrane are discussed in terms of the distribution function of bilayers formed within the filter paper.

Fibrosing properties, in the rat, of compounds related to dicetyl (di- n-hexadecyl) phosphate —I

In this preliminary survey, twenty-six compounds, related in one way or another to dicetyl(di- n-hexadecyl)phosphate, were compared with this substance as to tissue fibrosing activity by subcutaneous injections in the rat. Only dialkylphosphates (and the single alkylborate used) with a chain length of sixteen or eighteen carbon atoms were active. The only substance with unsaturated alkyl chains, dioleyl(C 18)phosphate, was inactive. Dicholesteryl-phosphate and phosphite were not active. None of the phosphites (di- or tri-) was active. Dicetylborate produced less flbrosis than the phosphate and this was accompanied by marked eosinophilia and subsequent encapsulated necrosis. Dioctadecyl phosphate was indistinguishable in these experiments from dicetyl phosphate.