Planar Bilayer Membranes Research Articles

Purified epithelial Na+ channel complex contains the pertussis toxin-sensitive G alpha i-3 protein.

We have recently demonstrated that the amiloride-sensitive Na+ channel in the apical membrane of the renal epithelial cell line, A6, is modulated by the alpha i-3 subunit of the Gi-3 protein. We also showed that a 700-kDa protein complex can be purified from the membranes of A6 epithelia which (a) can reconstitute the amiloride-sensitive Na+ influx in liposomes and planar bilayer membranes and (b) consists of six major protein bands observed on reducing sodium dodecyl sulfate-polyacrylamide gels with molecular masses ranging from 35 to 320 kDa. The present study was undertaken to determine if the alpha i-3 subunit was a member of this Na+ channel complex. G alpha i structure and function were identified by Western blotting with specific G alpha i subunit antibodies and Na+ channel antibodies, through ADP-ribosylation with pertussis toxin, and by immunocytochemical localization of the Na+ channel and G alpha i proteins. We demonstrate that two protein substrates are ADP-ribosylated in the 700-kDa complex in the presence of pertussis toxin and are specifically immunoprecipitated with an anti-Na+ channel polyclonal antibody. One of these substrates, a 41-kDa protein, was identified as the alpha i-3 subunit of the Gi-3 protein on Western blots with specific antibodies. Na+ channel antibodies do not recognize G alpha i-3 on Western blots of Golgi membranes which contain alpha i-3 but not Na+ channel proteins, nor do they immunoprecipitate alpha i-3 from solubilized Golgi membranes; however, alpha i-3 is coprecipitated as part of the Na+ channel complex from A6 cell membranes by polyclonal Na+ channel antibodies. Both alpha i-3 and the Na+ channel have been localized in A6 cells by confocal imaging and immunofluorescence with specific antibodies and are found to be in distinct but adjacent domains of the apical cell surface. In functional studies, alpha i-3, but not alpha i-2, stimulates Na+ channel activity. These data are therefore consistent with the localization of Na+ channel activity and modulatory alpha i-3 protein at the apical plasma membrane, which together represent a specific signal transduction pathway for ion channel regulation.

Identification of a membrane protein from T84 cells using antibodies made against a DIDS-binding peptide.

The outwardly rectified chloride channel of secretory epithelial cells is inhibited by disulfonic stilbene (DS) compounds such as 4,4'-diisothiostilbene-2,2'-disulfonic acid (DIDS) [R. J. Bridges, R. T. Worrell, R. A. Frizzell, and D. J. Benos, Am. J. Physiol. 256 (Cell Physiol. 25): C902-C912, 1989]. A 13-amino acid peptide (P49) corresponding to the putative DS binding site region of the murine anion exchange protein was synthesized, and polyclonal antibodies were generated against it and then purified over a P49 affinity column. The resulting monospecific antibodies reacted on Western blots with a 95- to 100-kDa protein from human erythrocytes and a 55- to 60-kDa protein from the human colonic tumor cell line, T84. The reaction with T84 protein did not appear to represent recognition of an anion exchanger because anion efflux from T84 cells was independent of external Cl-. In addition, monoclonal antibodies raised against human band 3 recognized the band 3 protein in human red cell ghost preparations but recognized nothing in T84 cell membrane preparations. In T84 cells, DIDS protected the 60-kDa protein from antibody binding. The anti-P49 antibody blocked outwardly rectified Cl- channels incorporated into planar lipid bilayer membranes from rat colon. Immunocytochemical data reveal specific binding of the anti-P49 antibody to perinuclear cytoplasmic vesicles. Forskolin caused these antibody-labeled vesicles to migrate from the perinuclear region to the plasma membrane under conditions and with a time course identical to that seen for stimulation of Cl- transport in these cells. Our results suggest that the protein may be a part of a chloride channel complex of secretory epithelial cells.

Developing biosensors with pH-ISFET transducers utilizing lipid bilayer membranes with transport proteins

We present a biosensor based on the transport protein lactose permease (LP) which is imbedded in a supported planar lipid bilayer (SPB) membrane, and which allows the potentiometric detection of lactose via pH measurement. Different experimental setups were used to study systematically the electric properties of the different biosensor components. In a first step the preparation of the SPB is investigated by means of high-frequency capacitance—voltage measurements. The sensor consists of an ion-sensitive field-effect transistor (ISFET) coated with the SPB membrane, the latter containing the lactose/H + cotransporter LP from Escherichia coli ( E. coli). The sensor effect consists of a rise in the proton concentration in the small volume between the lipid membrane and the gate area upon addition of lactose to the external medium. This effect is monitored directly by the pH-sensitive ISFET.

Gravity effects on biological systems

Theoretical investigations of the membrane-solution interface predict different effects of gravity on vertically and horizontally oriented planar membranes. Single channel events of gramicidin incorporated into phosphatidylserine planar bilayer membranes were measured in 0.1 M KCl solution, pH 7, at room temperature. The potential difference across the membrane was set to +/- 70 mV. The mean channel current was observed to be about 20% higher in horizontally oriented membranes compared to vertical membranes. This is in good agreement with the theoretical considerations and demonstrates that gravity does affect membrane processes by interaction with the membrane-solution interface which is a ubiquitous structure in biological systems.

Planar bilayer membranes from photoactivable phospholipids

Planar bilayer membranes formed from photoactivable phospholipids have been characterized by low frequency voltametry. Cyclic voltametric measurements were applied for simultaneous registration of planar membrane conductivity and capacitance. The procedure has been utilized to characterize the formation and stability of planar bilayer membranes. Bilayer membranes were formed from N′-(1,2-dimyristoyl- sn-glycero-3-phosphoethyl)- N-(( m-3-trifluoromethyldiazirine)phenyl)thiourea (C 14-PED), a head-group photosensitive phospholipid. In situ photoactivation of C 14-PED at wavelengths ≧ 320nm altered neither the mean conductivity nor the capacitance of the bilayer. Ionophore (valinomycin) and ion channel (gramicidin) activities were not impaired upon photoactivation. In contrast, bilayer membranes formed from 1,2-bis(hexadeca-2,4-dienoyl)- sn-glycero-3-phosphocholine (C 16-DENPC) revealed short life times. In situ photopolymerization of the diene fatty acids significantly increased the membrane conductivity or led to membrane rupture.

Colonic Cl channel blockade by three classes of compounds

We compared the potency and inhibitory actions of three different classes of organic acids on a Cl channel derived from colonic enterocyte plasma membrane vesicles. Chloride channels were incorporated into planar lipid bilayer membranes to examine the effects of the anthranilic acids, diphenylamine 2-carboxylic acid (DPC) and 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), the indanyl alkanoic acids, 2-[(2-cyclopentyl-6,7-dichloro-2,3-dihydro-2-methyl-1-oxo-1H-inden -5-yl)oxy] acetic acid (IAA-94) and its stereoenantiomer IAA-95, and the disulfonic stilbene, 4,4'-dinitro-stilbene-2,2'-disulfonic acid (DNDS). Except for DNDS, each of the blockers was equipotent from both the outer membrane and the cytoplasmic side of the channel protein. The potency order from the outmembrane side was DNDS greater than IAA-94 = IAA-95 greater than NPPB much greater than DPC. In contrast, the potency order from the cytoplasmic side was IAA-94 = IAA-95 greater than NPPB greater than DNDS much greater than DPC. DPC and NPPB caused a concentration-dependent decrease in the single-channel conductance (fast block). DNDS, IAA-94, and IAA-95 caused a flickery-type block and a concentration-dependent decrease in open-channel probability. Kinetic analysis revealed that blockade could be explained by a linear closed-opened-blocked kinetic scheme. Similarities in the electrostatic potential maps of these open-channel blockers suggest they may bind to a single shared binding site within the channel protein.

Identification of a translocated gating charge in a voltage-dependent channel. Colicin E1 channels in planar phospholipid bilayer membranes.

The availability of primary sequences for ion-conducting channels permits the development of testable models for mechanisms of voltage gating. Previous work on planar phospholipid bilayers and lipid vesicles indicates that voltage gating of colicin E1 channels involves translocation of peptide segments of the molecule into and across the membrane. Here we identify histidine residue 440 as a gating charge associated with this translocation. Using site-directed mutagenesis to convert the positively charged His440 to a neutral cysteine, we find that the voltage dependence for turn-off of channels formed by this mutant at position 440 is less steep than that for wild-type channels; the magnitude of the change in voltage dependence is consistent with residue 440 moving from the trans to the cis side of the membrane in association with channel closure. The effect of trans pH changes on the ion selectivity of channels formed by the carboxymethylated derivative of the cysteine 440 mutant independently establishes that in the open channel state, residue 440 lies on the trans side of the membrane. On the basis of these results, we propose that the voltage-gated opening of colicin E1 channels is accompanied by the insertion into the bilayer of a helical hairpin loop extending from residue 420 to residue 459, and that voltage-gated closing is associated with the extrusion of this loop from the interior of the bilayer back to the cis side.

One-sided action of amphotericin B on cholesterol-containing membranes is determined by its self-association in the medium

The inducement of K+ permeability through membranes by the polyene antibiotic amphotericin B (AmB) has been analyzed as a measure of the antibiotic activity. Dose-response curves have been obtained with cholesterol- and ergosterol-containing egg yolk phosphatidylcholine large unilamellar vesicles (LUVs), human erythrocytes, and Saccharomyces cerevisiae cells. Conductance changes induced by AmB in sterol-containing planar bilayer membranes have also been studied. AmB self-association in aqueous buffer was determined by circular dichroism (CD) as a function of the antibiotic concentration. Electronic absorption and CD spectra of AmB were recorded in the presence of LUVs. For given AmB concentrations, the extent of permeability inducement is dependent on the lipid concentration. On the other hand, for cholesterol-containing LUVs or erythrocytes, a critical AmB concentration had to be reached before any permeability is observed. Independent of lipid concentration, this concentration was directly related to antibiotic self-association in the aqueous buffer. The same observation was made for erythrocytes and nystatin. The AmB absorption and CD spectra were totally different for ergosterol- and cholesterol-containing LUVs. Formation of single channels by one-sided addition of AmB could be observed only in ergosterol-containing membranes. These data lead us to propose that the permeability pathways induced by amphotericin B or nystatin, in ergosterol- and in cholesterol-containing membranes, are of different natures. In the latter case the antibiotics are only active, by single-sided addition, in the self-associated form. These findings offer important clues for the design of less toxic derivatives of AmB: they should have a low degree of self-association in water.

The role of N-acetylneuraminic (sialic) acid in the pH dependence of influenza virion fusion with planar phospholipid membranes.

It is known that fusion of influenza virus to host cell membranes is strongly promoted by acidic pH. We have determined conditions required to obtain pH-dependent fusion of influenza virus to planar bilayer membranes. The rate of viral fusion was determined from the flash rate of R18-labeled virions delivered to the surface of the planar membrane by pressure-ejection from a pipette. For a bilayer formed only of phospholipids and cholesterol, the fusion rate was independent of pH and unaffected by the phospholipid composition. When the gangliosides GD1a + GT1b were included in the planar membrane, however, the fusion rate varied steeply with pH. The rate at pH 7.4 in the presence of the gangliosides was about an order of magnitude less than in their absence. At pH less than approximately 5.5, the rate was about an order of magnitude greater in the presence of gangliosides than in their absence. The fusion rate with planar membranes containing globoside, a ceramide-backboned glycolipid, was also independent of pH, indicating that the pH dependence required sialic acid on the carbohydrate moiety of the glycolipid. The gangliosides GM1a and GM3, both of which possess sialic acid, produced the same pH-dependent fusion rate as seen with GD1a + GT1b, indicating that the presence, but not the location, of terminal sialic acids is critical. Incubating virus with soluble sialyllactose blocked fusion to both ganglioside-free and ganglioside-containing planar membranes. These results show that the pH dependence of influenza virion fusion arises from the interaction of the sialic acid receptor with the influenza hemagglutinin. A model for sialic acid-hemagglutinin interactions accounting for pH-dependent fusion is presented.

Formation of ion channels in planar lipid bilayer membranes by synthetic basic peptides

We made use of a planar lipid bilayer system to examine the action of synthetic basic peptides which model the prepiece moiety of mitochondrial protein precursors and have antibacterial activity against Gram-positive bacteria. The sequences of the peptides used were as follows: Ac-(Ala-Arg-Leu) 3-NHCH 3 (3 3), Ac-(Leu-Ala-Arg-Leu) 2-NHCH 3 (4 2), ac-(Leu-Ala-Arg-Leu) 3-NHCH 3 (4 3), Ac-(Leu-Leu-Ala-Arg-Leu) 2-NHCH 3 (5 2). These peptides interacted differently with planar lipid bilayer membranes and membrane conductance increased by the formation of ion channels. The effects of the peptides on the macroscopic current-increase and on the prohability of channel formation, at the single channel level were in the order of 4 3 > 4 2 ≈ 5 2 ≫ 3 3, a finding which correlates with the antibacterial activity of these peptides. The micromolar (μM) order concentration at which the channel was formed resembles that causing antibacterial activity. Thus, the peptide antibacterial activity may occur through an increase in ion permeability of the bacterial membrane. The single-channel properties were investigated in detail using 4 3, the peptide with the highest ion channel-forming activity. Many types of channels were observed with respect to conductance (2–750 pS) and voltage dependency of gating. However, the channels were all cation-selective. These results suggest that the ion channels formed by peptide 4 3 may be able to take on a variety of conformations and/or assembly.

Electroporation: A unified, quantitative theory of reversible electrical breakdown and mechanical rupture in artificial planar bilayer membranes

We present a quantitative theory of electroporation of artificial planar lipid bilayer membranes. Assuming that aqueous pores are involved in electroporation, we describe the pore population of the membrane by the density function n ( r, t), where n ( r, t) d r is the number of pores with radius between r and r + d r at time t. We further assume that there is a minimum pore size r min, that pores of radius r min are created and destroyed by thermal fluctuations, and that the pore creation rate is proportional to exp( aΔφ m 2/ kT, where a is a constant, Δφ m is the membrane voltage, k is Boltzmann's constant, and T is the absolute temperature. We use a simple formula for the conductance of a pore as a function of radius, the expression for the pore energy previously derived by Pastushenko and Chizmadzhev, and a simple model of the external circuit. We solve the equations numerically and compare the solutions to the results of charge pulse experiments. In a charge-pulse experiment a membrane suffers one of four possible fates: (1) a slight increase in electrical conductance, (2) mechanical rupture, (3) incomplete reversible electrical breakdown, resulting in incomplete discharge of the membrane, or (4) reversible electrical breakdown (REB), resulting in complete discharge of the membrane. In agreement with experiment, this theory describes these four fates and predicts that the fate in any particular experiment is determined by the properties of the membrane and the duration and amplitude of the charging pulse.

Electroporation: a unified, quantitative theory of reversible electrical breakdown and mechanical rupture in artificial planar bilayer membranes

We present a quantitative theory of electroporation of artificial planar lipid bilayer membranes. Assuming that aqueous pores are involved in electroporation, we describe the pore population of the membrane by the density function n ( r, t), where n ( r, t) d r is the number of pores with radius between r and r + d r at time t. We further assume that there is a minimum pore size r min, that pores of radius r min are created and destroyed by thermal fluctuations, and that the pore creation rate is proportional to exp( aΔφ 2 m/ kT), where a is a constant, Δφ m is the membrane voltage, k is Boltzmann's constant, and T is the absolute temperature. We use a simple formula for the conductance of a pore as a function of radius, the expression for the pore energy previously derived by Pastushenko and Chizmadzhev, and a simple model of the external circuit. We solve the equations numerically and compare the solutions to the results of charge pulse experiments. In a charge-pulse experiment a membrane suffers one of four possible fates: (1) a slight increase in electrical conductance, (2) mechanical rupture, (3) incomplete reversible electrical breakdown, resulting in incomplete discharge of the membrane, or (4) reversible electrical breakdown (REB), resulting in complete discharge of the membrane. In agreement with experiment, this theory describes these four fates and predicts that the fate in any particular experiment is determined by the properties of the membrane and the duration and amplitude of the charging pulse.

Ionic channels induced by surfactin in planar lipid bilayer membranes

Surfactin is a lipopeptide produced by certain strains of Bacillus subtilis and has potent surface activity. Here, we present the first results showing that ion-conducting pores can be formed by surfac tin in artificial lipid membranes. With a low aqueous concentration of surfactin (1 μM) and a restricted membrane area (5·10 −5 cm 2) we observed conductance jumps that indicate the formation of individual ionic channels in the presence of K +, Rb +, Cs +, Na + or Li + chlorides. Although for every salt concentration ( C i ), the distribution in amplitude of the conductance steps ( Λ i ) may be rather broad, there is always a step amplitude which is more frequent than the others. In addition, the channels corresponding to this most frequent step amplitude are the longest in duration. For C i = 1 M, the cationic selectivity sequence deduced from these most frequent events is K + > Rb + > Na + > Cs + = Li + with respective values for Λ i M:130, 110, 80 and 30 pS. In KCl solutions Λ KCl M increases as a function of C i for low C i , and shows a plateau for C i > 0.5 M. When measured on larger area membranes (10 −2 cm 2) with 1 M solutions of the monovalent salts KCl, NaCl, RbCl and CsCl or the divalent salt CaCl 2, the macroscopic low voltage conductance ( G 0) increases with a slope of 2 on a log-log plot as a function of surfactin concentration. These results demonstrate that surfactin produces selective cationic channels in lipid bilayer membranes and suggest that at higher salt concentration, a dimer is involved in this functional channel-forming process.

Voltage-dependent block of anthrax toxin channels in planar phospholipid bilayer membranes by symmetric tetraalkylammonium ions. Effects on macroscopic conductance.

In a recent paper (Blaustein, R. O., T. M. Koehler, R. J. Collier, and A. Finkelstein, 1989. Proc. Natl. Acad. Sci. USA. 86:2209-2213) we described the general channel-forming properties of the PA65 fragment of anthrax toxin in planar phospholipid bilayer membranes. In the present paper we extend our previous studies of the permeability properties of this channel, using a series of symmetric tetraalkylammonium (TAA) ions. Our main finding is that at micromolar concentrations on either the cis (toxin-containing) or trans side of a membrane containing many (greater than 1,000) channels, these ions, ranging in size from tetramethylammonium to tetrahexylammonium, induce a voltage-dependent reduction of membrane conductance. (We attribute a similar voltage-dependent reduction of membrane conductance by millimolar concentrations of HEPES to a cationic form of this buffer present at micromolar concentrations.) In going from large negative to large positive voltages (on the TAA side) one sees that the conductance first decreases from its value in the absence of TAA, reaches a minimum, and then rises back at larger positive voltages toward the level in the absence of TAA. Our interpretation of this behavior is that these symmetric TAA ions block the cation-selective PA65 channel in a voltage-dependent manner. We postulate that there is a single site within the channel to which TAA ions can bind and thereby block the passage of the major current-carrying ion (potassium). A blocking ion is driven into the site by modest positive voltages, but is driven off the site and through the channel by larger positive voltages, thus explaining the relief of block. (In the accompanying paper [Blaustein, R. O., E. J. A. Lea, and A. Finkelstein. 1990. J. Gen. Physiol. 96:921-942] we confirm this interpretation of the data by analysis at the single-channel level.) This means that these blocking ions can pass through the channel; the permeability to tetrahexylammonium, the largest ion studied, implies that the narrowest part of the channel has a diameter of at least 11 A.

Diffusion limitation in the block by symmetric tetraalkylammonium ions of anthrax toxin channels in planar phospholipid bilayer membranes.

Current flow through the channel formed in planar phospholipid bilayer membranes by the PA65 fragment of anthrax toxin is blocked, in a voltage-dependent manner, by tetraalkylammonium ions (at micromolar concentrations), which bind to a blocking site within the channel lumen. We have presented evidence that diffusion plays a significant role in the kinetics of blocking by tetrabutylammonium ion (Bu4N+) from the cis (toxin-containing) side of the membrane (Blaustein, R. O., E. J. A. Lea, and A. Finkelstein. 1990. J. Gen. Physiol. 96:921-942); in this paper we examine the implications and consequences of diffusion control for binding kinetics. As expected for a diffusion-affected reaction, both the entry rate constant (kcis1) of Bu4N+ from the cis solution to the blocking site and the exit rate constant (kcis-1) of Bu4N+ from the blocking site to the cis solution are reduced if the viscosity of that medium is increased by the addition of dextran. In conformity with both thermodynamics and kinetic arguments, however, the voltage-dependent equilibrium binding constant, Keq (= kcis-1/kcis1), is not altered by the dextran-induced viscosity increase of the cis solution. The entry rate constants (kcis1) for tetrapentylammonium (Pe4N+), tetrahexylammonium (Hx4N+), and tetraheptylammonium (Hp4N+) are also diffusion controlled, and all of them, including that for Bu4N+, attain a voltage-independent plateau value at large positive cis voltages consistent with diffusion limitation. Although the plateau value of kcis1 for Hx4N+ is only a factor of 3 less than that for Bu4N+, the plateau value for Hp4N+ is a factor of 35 less. This precipitous fall in value indicates, from diffusion-limitation theory, that the diameter of the channel entrance facing the cis solution is not much larger than the diameter of Hp4N+, i.e., approximately 12 A.

Nystatin-induced liposome fusion. A versatile approach to ion channel reconstitution into planar bilayers

A simple method is described for promoting and detecting fusion of liposomes with planar bilayer membranes. Liposomes containing ergosterol are doped with the pore-forming antibiotic nystatin, and the planar bilayer is kept ergosterol-free. Under these conditions, when a transbilayer salt gradient is applied, liposomes added to the high-salt side of the bilayer elicit the appearance of abrupt conductance jumps of 5-300 pS. The increase in conductance is transient, decaying back to baseline on the order of 10 s. Each of these "spikes" represents the fusion of a single liposome with the bilayer, resulting in the simultaneous insertion of many nystatin channels. Relaxation of the conductance back to baseline occurs because ergosterol, required for the integrity of the nystatin pore, diffuses away into the sterol-free planar bilayer after liposome fusion. When Torpedo Cl- channels are reconstituted into liposomes containing ergosterol and nystatin, fusion spikes are observed simultaneously with the appearance of Cl- channels. This method allows the calculation of the density of functional ion channels in a preparation of proteoliposomes containing reconstituted channel protein.

Import‐defective colicin B derivatives mutated in the TonB box

The pore-forming colicin B is taken up into Escherichia coli by a receptor and TonB-dependent process. The receptor and colicin B both contain a similar amino acid sequence, close to the N-terminal end, termed the TonB box. Point mutations were introduced into the TonB-box region of the colicin B structural gene cba resulting in colicin B derivatives which were partially or totally inactive against E. coli cells. All derivatives still bound to the receptor. An inactive derivative killed cells when translocated across the outer membrane by osmotic shock treatment, and formed pores in planar lipid bilayer membranes identical to the wild-type colicin. Some of the mutations were partially suppressed by mutations in the tonB structural gene. It was concluded that the TonB-box mutations define a region that is involved in the uptake of colicin B across the outer membrane.

Diffusion-controlled binding of a peptide neurotoxin to its potassium channel receptor

Single Ca2(+)-activated K+ channels were reconstituted into planar lipid bilayer membranes, and the effect of charybdotoxin, a pore-blocking peptide from scorpion venom, was studied. In particular, the effect of solution viscosity on the kinetics of block was assessed in order to test the idea that toxin binding is diffusion-controlled. This idea is supported by the strictly inverse relation between solution viscosity and the rate constants of both association and dissociation of peptide with the K+ channel mouth. However, at an ionic strength high enough to suppress local electrostatic potentials, the diffusion-controlled on-rate constant is surprisingly low, 10(5) M-1 s-1. These slow, viscosity-dependent kinetics may be understood if charybdotoxin can attain the bound state only from a rare set of encounters with the K+ channel.

Colicin N forms voltage- and pH-dependent channels in planar lipid bilayer membranes

The protein antibiotic colicin N forms ion-permeable channels through planar lipid bilayers. Channels are induced when positive voltages higher than +60 mV are applied. Incorporated channels activate and inactivate in a voltage-dependent fashion. It is shown that colicin N undergoes a transition between an "acidic" and a "basic" channel form which are distinguishable by different voltage dependences. The single-channel conductance is non-ohmic and strongly dependent on pH, indicating that titratable groups control the passage of ions through the channel. The ion selectivity of colicin N channels is influenced by the pH and the lipid composition of the bilayer membrane. In neutral membranes the channel undergoes a transition from slightly cation-selective to slightly anion-selective when the pH is changed from 7 to 5. In lipid membranes bearing a negative surface charge the channel shows a more pronounced cation selectivity which decreases but does not reverse upon lowering the pH from 7 to 5. The high degree of similarity between the channel characteristics of colicin A and N suggests that the channels share common features in their molecular structure.

Electric field increases the phase transition temperature in the bilayer membrane of phosphatidic acid

The effect of the electric field on the phase transition temperature ( T c ) of acidic 1,2-dipalmitoyl- sn-glycero-3-phosphate (DPPA) and 1,2-dipalmitoyl- sn-glycero-3-thionphosphate (thion-DPPA) and zwitterion, i.e. 1,2-dipalmitoyl- rac-3-phosphocholine and 1,2-distearoyl- rac-glycero-3-phosphocholine (DPPC and DSPC), lipids has been investigated. The phase transition was detected using the jump-like increase effect in the conductance of the planar bilayer membrane. A voltage increase to 150 mV has been shown to increase the phase transition temperature in a bilayer lipid membrane (BLM) of phosphatidic acids (DPPA and thion-DPPA) by 8–12°C while the transition temperature in the bilayer of zwitterion lipids (DPPC and DSPC) increases insignificantly. The increasing of f t in BLM of acidic lipids is attributed to the voltage-induced changes in the molecule packing density.