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At least 19 recordsLinked to original sources
PubMed1992

The mode of action of Vibrio cholerae cytolysin. The influences on both erythrocytes and planar lipid bilayers.

The interaction with erythrocytes of cholera cytolysin (CC) obtained from a non-01 Vibrio cholerae strain results in the osmotic rupture of target cells upon formation by CC of the waterfilled pores in their membranes. The aggregation of several toxin monomers is required for the formation of one CC channel with a radius of 0.9-1.0 nm. The investigations using planar bilayer lipid membranes suggest that the CC-induced pore is an interprotein anion selective channel carrying a fixed positive charge. The role of the charge was supported by the influence of pH on the selectivity, single conductance and voltage gating of the CC channels. The ability of the CC to modify both model and natural membranes has a maximum at pH 6.0-7.0. It was found that CC channels insert into the membrane asymmetrically. The effect of proteolytic treatment of the channel by papain also indicates that the two entrances of the channel protrude from the plane of the membrane into the solution for different distances. It is proposed that the biological effects of the non-01 V. cholera cytolysin are based on its channel-forming activity.

Animals↗
PubMed1992

Comparison of 9-aminoacridine and atebrine induced changes in optical, electrical and mechanical characteristics of lipid bilayers.

The effects of fluorescent probes 9-aminoacridine (9AA) and atebrine (AT) on physical properties of liposomes and planar bilayer lipid membranes (BLM) were studied. The method of fluorescence spectroscopy and the electrostriction method based on measurement of higher current harmonics were used. At low concentrations (10(-5)-5 x 10(-5) mol/l), 9AA increased fluorescence intensity, while in liposomes from soybean phosphatidylcholine fluorescence quenching occurred at higher probe concentration. Fluorescence quenching occurred over the entire concentration range tested (10(-5)-10(-4) mol/l) in liposomes made from a mixture of egg phosphatidylcholine and cardiolipin. In contrast to 9AA, AT, thanks to its hydrophobic chain, penetrates deeper into the hydrophobic membrane moiety; thus, immobilization of the molecule and an increase in fluorescence intensity was always observed. Probes adsorbed to membranes, leaving their electric capacitance effectively unchanged. Adsorption of charged dye particles induced small changes in transmembrane potential. In the presence of 10(-5) mol/l AT, the modulus of elasticity E perpendicular increased somewhat for soft membranes (E perpendicular approximately 2.5 x 10(7) Pa), whereas it decreased for hard membranes (E perpendicular approximately 5 x 10(7) Pa). pH gradient present on the membrane affected the ability of the dyes to incorporate into the membranes. Our results provide evidence against the proposed model of the quenching mechanism introduced by Rottenberg and Lee (1975).

Aminacrine↗
PubMedDate not supplied

[Lipid oxidation in bilayer lipid membranes linked with the reaction of oxidation of NAD.H by atmospheric oxygen].

It is shown that along with NAD.H oxidation with air oxygen peroxide oxidation of lipids forming the membrane takes place in bilayer lipid membranes modified with ubiquinone. During nicotin amide oxidation proton absorption takes place. Peroxide oxidation of lipids results in the liberation of H+ ions, which in its turn brings about the formation of protone-deficient or enriched (against aqueous solution) layers adjacent to the membrane. The potential value on the membrane is shown to depend on nicotine amide and oxygen concentration, on ubiquinone presence and lipid composition of the membrane. It has been also indicated that the transmembrane potential difference is initiated with a sharp change of aqueous solution pH by 0.05--0.4 units.

Air↗
PubMed1976

Interaction of the polyene antibiotics with lipid bilayer vesicles containing cholesterol.

The interaction of the polyene antibiotics, amphotericin B, nystatin and filipin with cholesterol-containing single bilayer lipid vesicles has been characterized using gel permeation chromatography and proton magnetic resonance. All three antibiotics bind to vesicles at low concentrations without causing a large amount of vesicle destruction. The strength of binding as determined by gel permeation studies is greater for filipin and amphotericin than for nystatin. Nystatin and amphotericin B at these low concentrations induce a rapid loss of internal vesicle contents consistents consistent with pore formation. Filipin induces no leakage beyond that expected from partial vesicle destruction or general detergent action. At antibiotic levels above 1:1 antibiotic: cholesterol ratios the NMR results show all three antibiotics to cause extensive vesicle destruction. The onset of this behavior, which appears to be independent of the total antibiotic concentraion, indicates a well defined antibiotic : cholesterol interaction stoichiometry. Despite the fact that cholesterol is required for antibiotic activity, the NMR spectra prior to vesicle destruction show no changes indicative of an antibiotic-induced reversal of cholesterol restriction of phosphatidylcholine mobility. The contrast with polyene antibiotic behavior in more extended bilayers is discussed.

Amphotericin B↗
PubMed1978

Inner voltage clamping. A method for studying interactions among hydrophobic ions in a lipid bilayer.

Ketterer, et al. (1971) have suggested that a combination of electrostatic and chemical interactions may cause hydrophobic ions absorbed within a bilayer lipid membrane to reside in two potential wells, each close to a membrane surface. The resulting two planes of charges would define three regions of membrane dielectric: two identical outer regions each between a plane of absorbed charges and the plane of closest approach of ions in the aqueous phase; and the inner region between the two planes of adsorbed charges. The theory describing charge translocation across the inner region is based on a simple three-capacitor model. A significant theoretical conclusion is that the difference between the voltage across the inner region, V(i), and the voltage across the entire membrane, V(m), is directly proportional to the amount of charge that has flowed in a voltage clamp experiment. We demonstrate that we can construct an "inner voltage clamp" that can maintain, with positive feedback, a constant inner voltage, V(i). The manifestation of proper feedback is that the clamp current (after a voltage step) will exhibit pure (i.e., single time-constant) exponential decay, because the voltage dependent rate constants governing translocation will be independent of time. The "pureness" of the exponential is maximized when the standard deviation of the least-square fit of the appropriate exponential equation to the experimental data is minimized. The concomitant feedback is directly related to the capacitances of the inner and outer membrane regions, C(i) and C(o).Experimental results with tetraphenylborate ion adsorbed in bacterial phosphatidylethanolamine/n-decane bilayers indicate C(i) approximately 5 . 10(-7)F/cm(2) and C(o) approximately 5 . 10(-5)F/cm(2).

Bacteria↗
PubMed1978

The interaction of bee melittin with lipid bilayer membranes.

The influence of melittin and the related 8-26 peptide on the stability and electrical properties of bilayer lipid membranes is reported. Melittin, unlike the 8-26 peptide, has a dramatic influence on lipid membranes, causing rupture at dilute concentrations. The circular dichroism of melittin demonstrated that under physiological conditions, in water, melittin is in extended conformation, which is enhanced in aqueous ethanol. However in 'membrane-like' conditions it is essentially alpha-helical. Secondary structure predictions were used to locate possible alpha-helical nucleation centres and a model of melittin was built according to these predictions. It is postulated that melittin causes a wedge effect in membranes.

Bee Venoms↗
PubMedDate not supplied

[Piezoeffect, baseline conductivity and filtration coefficients of lipid bilayer membrane].

A piezoeffect in bilayer lipid membranes (BLM), i.e. a generation of alternate electrical current y through a membrane under alternate pressure gradient in the absence of constant transmembrane potential is investigated. It is shown that y is not connected with the membrane deformations, it is generated with electroosmotic flow of K+ ions, its amplitude increases with a rise of BLM phonic conductance and is probably connected with defects in BLM structure. The value of the filtration coefficient Lp is estimated.

Chemical Phenomena↗
PubMed1977

The molecular organization of asymmetric lipid bilayers and lipid-peptide complexes.

Oriented fatty acid bilayers with asymmetric distributions of lipid head group types, hydrocarbon chain lengths, and associated polypeptides have been analyzed by a combined use of high resolution electron microscopy and X-ray diffraction techniques. The exclusion of fixatives, stains, and embedding materials has made it possible to relate unequivocally microscopic images to molecular composition. The ultrastructure of asymmetric bilayers has been determined by a novel analysis in which one half of the bilayer serves as a structural reference for the entire bilayer. Absolute electron density profiles at 7 A resolution have been computed for bilayers formed from long and short chain length lipids either segregated to opposite sides or mixed together in both sides of the bilayer. The data indicate that the two lipids self organize in a specific paired configuration. Detailed analysis of bilayers associated with poly-L-lysine shows that although this hydrophilic peptide resides near the lipid head group region, its presence alters the arrangement of the bilayer hydrocarbon chains.

Barium↗
PubMed1977

Properties of lipid bilayer membranes made from lipids containing phytanic acid.

Besides the preparation of phytanic acid (3,7,11,15-tetramethylhexadecylic acid) according to the Dumas-Stass reaction, the synthesis of four different lipids containing phytanic acid residues is described. Diphytanoyl phosphatidylcholine was synthesized beginning from glycerylphosphorylcholine, whereas the other lipids, diphytanoyl phosphatidylethanolamine, diphytanoyl phosphatidylserine and monophytanoyl glyceride were prepared by total synthesis. Some properties of lipid bilayer membranes made from the lipids containing phytanic acid were investigated. The specific capacity of these membranes was measured. Its value of approximately 400 nF cm-2 was found to be similar to the value of membranes from lipids with unbranched fatty acid residues. Charge pulse experiments were performed using dipicrylamine as a molecular probe of membrane structure. The results were discussed on the basis of a higher viscosity of the membranes from lipids containing phytanic acid residues compared with unbranched fatty acid residues.

Amines↗
PubMed1976

Interaction of charged lipid vesicles with planar bilayer lipid membranes: detection by antibiotic membrane probes.

A technique has been developed for monitoring the interaction of charged phospholipid vesicles with planar bilayer lipid membranes (BLM) by use of the antibiotics Valinomycin, Nonactin, and Monazomycin as surface-charge probes. Anionic phosphatidylserine vesicles, when added to one aqueous compartment of a BLM, are shown to impart negative surface charge to zwitterionic phosphatidylcholine and phosphatidylethanolamine bilayers. The surface charge is distributed asymmetrically, mainly on the vesicular side of the BLM, and is not removed by exchange of the vesicular aqueous solution. Possible mechanisms for the vesicle-BLM interactions are discussed.

Anti-Bacterial Agents↗
PubMed1979

The rotational diffusion of cytochrome b5 in lipid bilayer membranes. Influence of the lipid physical state.

A derivative of the integral membranes protein, cytochrome b5, has been prepared in which the native heme group has been replaced by the structurally similar rhodium(III)-protoporphyrin IX. This metalloporphyrin has a finite triplet yield with a single exponential decay time of 22 microsecond in water. After insertion of the metalloporphyrin into the protein, its triplet-state decay becomes strongly nonexponential with at least three equal amplitude components with time constants varying over a range of 100. The derivatized protein has been incorporated into unilamellar liposomes prepared from dimyristoyllecithin, and the rotational diffusion of the protein in the lipid bilayer has been studied at temperatures above and below the lipid phase transition temperature via triplet absorbance anisotropy decay. The anisotropy decay curves are biphasic both above and below the lipid phase transition. The rotational diffusion constant is found to be 2.4 X 10(5) s-1 at 35 degrees C, and 1.1 X 10(4) s-1 at 10 degrees C, both being calculated from the fast decay component. The ratio of the limiting anisotropy to the initial anisotropy is 0.6 at both temperatures. This implies a cone of restricted motion of 34 degrees for the protein in the bilayer.

Animals↗
PubMed1978

Voltage-induced reflectivity relaxation of bilayer lipid membranes: on changes of bilayer thickness.

Temporal and voltage-induced changes of reflectivity (R), the optical phase difference in transmitted polarized light, of tension and total capacity of bilayer lipid membrane (BLM) were studied. The membranes were mainly formed from total brain phospholipids (TP) in n-alkanes. 1) Reflectivity of "black" regions of films made of TP in decane and hexadecane decreases by several percent with a time constant (tauR) of about 30 min, whereas that of membranes with hexane and heptane does not depend on time (with an accuracy up to 1--2%). The BLM tension decreases appreciably in the course of time and reaches its steady-state value in tens of minutes after complete blackening of the membrane. 2) Under prolonged (up to tens of minutes) action of voltage (V) no R changes of BLMs with hexane, heptane, and hexadecane were revealed at a noise level of 0.2%. Blms with decane usually respond to voltage application, first by a rapid (jump-like) and then by a slow decrease of R with a value spread from 0.2% to 3%. 3) With higher amplitude and temporal resolutions of the signal (signal averaging method) it can be seen that after voltage jump R decreases down to a new steady-state value: at V = 100 mV, deltaR/R = -(2--4) . 10(-4) and tauR approximately 0.1 msec for BLMs from TP in heptane, and deltaR/R = -(3--6) . 10(-2) and tauR approximately 2 msec for BLMs from oxidized cholesterol in decane. It is shown in the latter case that the great value of deltaR/R is due to the contribution of invisible microlenses. In all the cases deltaR approximately V2. 4) It is concluded that at voltage jump a bilayer first becomes thinner due to volumic compression of its hydrocarbon core; then it spreads with a time constant of the order of 0.1 msec, getting thinner until a new equilibrium state is reached. Complete change of bilayer thickness is detah/h approximately -10(-4) at 100 mV.

Alkanes↗
PubMedDate not supplied

[Properties of bilayer lipid membranes formed from cholesterol and alkyltrimethylammonium bromides].

Flat bilayer lipid membranes (BLM) were obtained from cholesterol solution in n-octane in the presence of detergents of alkyltrimethyl ammonium bromides series in water medium. It has been shown that highly stable BLM are obtained only for the detergents of this series with the alkyl chain higher than C12. Changes in stability and electromechanical strength of the latter are conditioned by the peculiarities of stechiometric interaction between the molecules of cholesterol, detergent and solvent in the lipid bilayer.

Bromides↗
PubMed1992

Electron spin resonance study on the permeability of superoxide radicals in lipid bilayers and biological membranes.

The permeability of lipid bilayers and biological membranes to superoxide free radicals was examined by using superoxide dismutase (SOD)-loaded lipid vesicles and SOD-loaded erythrocyte ghosts. After exposing SOD lipid vesicles and SOD ghosts to enzymatically produced superoxide radicals and using spin-trapping and electron spin resonance (ESR) techniques, we found that SOD entrapped within erythrocyte ghosts effectively scavenges external O2.- while SOD inside the lipid bilayers has no effect. These results confirm that O2.- is able to cross through a biological plasma membrane but not across a pure lipid bilayer. The data provide instruction as to how and where anti-oxidant therapy is to be approached relative to the site of oxygen free radical production.

Cell Membrane Permeability↗
PubMed1992

Ca(2+)-activated K+ channels from an insulin-secreting cell line incorporated into planar lipid bilayers.

This study evaluates the use of the planar lipid bilayer as a functional assay of Ca(2+)-activated K+ channel activity for use in purification of the channel protein. Ca(2+)-activated K+ channels from the plasma membrane of an insulin-secreting hamster Beta-cell line (HIT T15) were incorporated into planar lipid bilayers. The single channel conductance was 233 picoSiemens (pS) in symmetrical 140 mmol/l KCl and the channel was strongly K(+)-selective (PCl/PK = 0.046; PNa/PK = 0.027). Channels incorporated into the bilayer with two orientations. In 65% of cases, the probability of the channel being open was increased by raising calcium on the cis side of the bilayer (to which the membrane vesicles were added) or by making the cis side potential more positive. At a membrane potential of + 20 mV, which is close to the peak of the Beta-cell action potential, channel activity was half-maximal at a Ca2+ concentration of about 15 mumol/l. Charybdotoxin greatly reduced the probability of the channel being open when added to the side opposite to that at which Ca2+ activated the channel. These results resemble those found for Ca(2+)-activated K+ channels in native Beta cell membranes and indicate that the channel properties are not significantly altered by incorporation in a planar lipid bilayer.

Animals↗
PubMed1977

Structure of the gramicidin A channel: discrimination between the piL,D and the beta helix by electrical measurements with lipid bilayer membranes.

Measurements with different chemically modified gramicidins in lipid bilayer membranes were used to discriminate between the dimeric pi(L,D) helix proposed by Urry and the dimeric parallel or antiparallel helices proposed by Veatch and Blout. Evidence for the pi(L,D) helix was obtained on the basis of the different actions of a negatively charged O-pyromellitylgramicidin and a negatively charged N-pyromellityldesformylgramicidin on lipid bilayer membranes. O-Pyromellitylgramicidin forms ionic channels in lipid membranes when it is applied to both sides of the membrane. In contrast to unmodified gramicidin, O-pyromellitylgramicidin is inactive when it is applied only to one side of the membrane. N-Pyromellityldesformylgramicidin does not form ionic channels in lipid bilayer membranes whether it is applied to one or both sides of the membrane. These results support the view that the gramicidin channel is formed by two pi(L,D) helices. Dimer formation by head-to-head association of two pi(L,D) helices needs six intermolecular hydrogen bonds, which are located at the formyl end of the molecule and which occur deep within the lipid membrane. In the head-to-head associated pi(L,D) helix the absence of the formyl group leads to an inactivation of the peptide, whereas in a parallel or antiparallel double-stranded helix the absence of the formyl group should have only minor effects.

Electric Conductivity↗
PubMed1976

Some similarities between processes at biological membranes and lipid bilayers.

Several processes at biological membranes can be simulated by experiments with artificial lipid bilayer membranes. Three selected examples are discussed: The uncoupler induced proton permeability of lipid bilayers, the initiation of action potential like voltage responses in lipid membranes, and the reconstitution of active cation pumps across planar lipid bilayers or lipid vesicles.

Lipids↗