Planar Bilayer Lipid Membranes

TH Tien, A Ottova-Leitmannova. Membrane Biophysics as Viewed from Experimental Bilayer Lipid Membranes Planar Lipid Bilayers and Spherical Liposomes. New York Elsevier Science, 2000. 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

H.T. Tien, A. L. Ottova, Membrane Biophysics As Viewed From Experimental Bilayer Lipid Membranes (planar lipid bilayers and spherical iposomes), Elsevier, Amsterdam, New York, 2000, p. 648. 

This review addresses the issues of the chemical and physical processes whereby inorganic anions and cations are selectively retained by or passed through cell membranes. The channel and carrier mechanisms of membranes permeation are treated by means of model systems. The models are the planar lipid bilayer for the cell membrane, Gramicidin for the channel mechanism, and Valinomycin for the carrier mechanism. 

As first shown by Hladky and Haydon 7,8), it is possible to observe the current due to a single transmembrane channel by using extensions of the planar lipid hilaver approach of Mueller and Rudin 9). The basic system is shown in Fig. 2 and is commonly referred to as the black lipid membrane (BLM) method. This is because, as the lipid in the hole between the two chambers thins, the areas that have become planar bilayers are seen as black. Additional terms are bilayer lipid membranes or planar lipid bilayer membranes. These lipid bilayer membranes, particularly those which are solvent free, have capacitances which are very close to those of biological membranes. 

Pharmacological Methods and Results. The data upon which the following discussion is based were accumulated using three techniques mouse bioassay, displacement of radiolabelled saxitoxin from rabbit brain membranes, and blockage of sodium conductance through rat sarcolemmal sodium channels incorporated into planar lipid bilayers. The results are summarized in Figures 11 and 12. 

Tamplin et. al. (54) observed that V. cholerae and A. hydrophila cell extracts contained substances with TTX-like biological activity in tissue culture assay, counteracting the lethal effect of veratridine on ouabain-treated mouse neuroblastoma cells. Concentrations of TTX-like activity ranged from 5 to 100 ng/L of culture when compared to standard TTX. The same bacterial extracts also displaced radiolabelled STX from rat brain membrane sodium channel receptors and inhibited the compound action potential of frog sciatic nerve. However, the same extracts did not show TTX-like blocking events of sodium current when applied to rat sarcolemmal sodium channels in planar lipid bilayers. 

The purified membrane bound Na,K-ATPase from kidney adsorbs to planar lipid bilayers and transient currents can be elicited upon release of caged ATP [99,100], The... 

Kagan, B.L., et al., Antimicrobial defensin peptides form voltage-dependent ion-permeable channels in planar lipid bilayer membranes, Proc. Natl. Acad. Sci. U. S.A. 87,1,210,1990. 

In addition, some flavonoids can differentially interact with membrane polar surfaces or penetrate into the bilayer, depending on certain characteristics of the reaction milieu. This is the case of quercetin, a flavonoid that at acidic pH is deeply embedded into planar lipid bilayers [Movileanu et al., 2000], while at... 

Ions and small molecules may be transported across cell membranes or lipid bilayers by artificial methods that employ either a carrier or channel mechanism. The former mechanism is worthy of brief investigation as it has several ramifications in the design of selectivity filters in artificial transmembrane channels. To date there are few examples where transmembrane studies have been carried out on artificial transporters. The channel mechanism is much more amenable to analysis by traditional biological techniques, such as planar bilayer and patch clamp methods, so perhaps it is not surprising that more work has been done to model transmembrane channels. 

Complexes of the two polymers, isolated from bacterial plasma membranes or prepared from synthetic polymers, form voltage-dependent, Ca2+-selective channels in planar lipid bilayers that are selective for divalent over monovalent cations, permeant for Ca2+, Sr2+... 

Rytomaa, M., and Kinnunen, P.KJ., 1995, Reversibility of the binding of cytochrome c to liposomes. Implications for lipid-protein interactions. /. Biol. Chem., 270 3197-3202 Salamon, Z., and Tollin, G., 1996, Surface plasmon resonance studies of complex formation between cytochrome c and bovine cytochrome c oxidase incorporated into a supported planar lipid bilayer. II. Binding of cytochrome c to oxidase-containing cardiolipin /phosphatidylcholine membranes. Biophys. J., 71 858-867 Salamon, Z., and Tollin, G., 1997, Interaction ofhorse heart cytochrome c with lipid bilayer membranes effects on redox potentials. J. Bioenerg. Biomembr. 29 211-221 Scarlett, J.L., and Murphy, M.P., 1997, Release of apoptogenic proteins from the... 

Wagner ML, Tamm LK (2000) Tethered polymer-supported planar lipid bilayers for reconstitution of integral membrane proteins Silane-polyethyleneglycol-lipid as a cushion and covalent linker. Biophys J 79 1400-1414... 

Arora, A., Rinehart, D., Szabo, G., and Tamm, L. K. (2000). Refolded outer membrane protein A of Escherichia coli forms ion channels with two conductance states in planar lipid bilayers. J. Biol. Chem. 275, 1594 1600. 

Fig. 8. Proton activation of KcsA. (A) Time course of 86Rb+ uptake depends on ex-travesicular pH. Open circles, uptake at pH 7.0 (left) or 3.5 (right). Filled circles, uptake in the presence of 10 mM BaClg in both sides of the membrane. (B) pH effect on singlechannel properties of KcsA in planar lipid bilayers. Top Consecutive single-channel traces obtained at pH 4.0, 4.5, 5.0 and 6.0 for a multichannel asolectin bilayer. Bottom panels All-point histogram corresponding to each set of single-channel records.

The interaction of CNTs with membrane bilayers has been studied mainly with model membrane systems, and limited data have been obtained in vivo. Available evidence indicates that at low pH TeTx and BoNTs undergo a conformational change from a water soluble "neutral" form to an "acidic" form, the latter characterized by the exposure of hydrophobic segments. This increase in hydrophobicity allows penetration of both the H and L chains into the hydrocarbon core of the lipid bilayer (Montecucco etal., 1994). Following this low pH-induced membrane insertion, TeTx and BoNTs form ion channels in planar lipid bilayers (Beise et al., 1994 Montecucco et al., 1994). These channels are cation-selective, have few tens of pS conductance and are per-... 

As an altemative approach to MAS experiments on immobilized proteins, membrane proteins may be incorporated into planar lipid bilayers, which may be uniaxially oriented with the bi layer normal parallel to the external magnetic field. This implies that the sample will display single-crystal like spectra and hence sample spinning is not needed to provide high resolution. In this section, we will numerically investigate some of the fundamental aspects one needs to consider when performing experiments on uniaxially oriented membrane proteins. 

Structural and functional studies of a synthetic peptide that mimics a proposed membrane inserting segment of a Bacillus thuringiensis delta-endotoxin have been conducted. An NMR study of a methanol solution of a synthetic 31-mer peptide corresponding to the sequence of a putative pore-forming segment of the CrylA(c) toxin showed that the peptide exists as an a-helix. Hie peptide forms discrete, characterizable channels in planar lipid bilayers. It is possible that this helix is a component of the transmembrane pore formed by Bacillus thuringiensis delta-endotoxins in vivo. 

Regulation by neurotoxins. J Gen Physiol 76 287-313 Krueger BK, Worley JF, French RJ (1983) Single sodium channels from rat brain incorporated into planar lipid bilayer membranes. Nature 303 172-175 Lawrence JC, Catterall WA (1981) Tetrodotoxin-insensitive sodium channels. Ion flux studies of neurotoxin action in a clonal rat muscle cell line. J Biol Chem 256 6213-6222... 

Among the different available preparation techniques, direct formation of planar lipid bilayers from unilamellar vesicles is the most widespread method for obtaining solvent-free model membranes providing the required platform to study adsorption of proteins. 

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