Planar lipid bilayers

Protems can be physisorbed or covalently attached to mica. Another method is to innnobilise and orient them by specific binding to receptor-fiinctionalized planar lipid bilayers supported on the mica sheets [15]. These surfaces are then brought into contact in an aqueous electrolyte solution, while the pH and the ionic strength are varied. Corresponding variations in the force-versus-distance curve allow conclusions about protein confomiation and interaction to be drawn [99]. The local electrostatic potential of protein-covered surfaces can hence be detemiined with an accuracy of 5 mV. 

Knowles, B. H., Blatt, M. R., Tester, M., et al., 1989. A cytosolic 5-endo-toxin from Bacillus thurigiensis var. israelensis forms cation-selective channels in planar lipid bilayers. FEES Letters 244 259-262. 

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. 

Fig. 2. Experimental set up for characterizing channel or carrier induced currents crossing the small area of a planar lipid bilayer which is schematically shown in enlarged view. Net current derives from either an applied potential or a concentration gradient...

A. Side view of channel spanning the lipid layer of a planar lipid bilayer, The structure is comprised of two monomers, each in a left-handed, single stranded p -helical conformation, and joined together at the head or formyl end by means of six, intermolecular hydrogen bonds. The two formyl protons are seen at the center of the structure in this view. Replacement of these protons by methyls destabilizes the conducting dimer as shown with N-acetyl desformyl Gramicidin A (Fig. 3D). 

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. 

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... 

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... 

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. 

Subsequently the ion channel activity was tested by single-channel current measurements using planar lipid bilayers. Single-channel conductances of ca. 55 in 500 mM NaCl and 65 pS in KCl were obtained. The weak ion selectivity was claimed to reflect a slightly larger mobility of K compared to that of Na ion in bulk solution. Therefore a large 7.5-A pore structure in lipid bilayers is assumed to resemble the bulk aqueous solution. 

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... 

Movileanu L, Neagoe I, Flonta ML. 2000. Interaction of the antioxidant flavonoid quercetin with planar lipid bilayers. Int J Pharm 205 135-146. 

Figure 2. Httexp amino-terminal fragment sensitizes InsP3Rl to activation by InsP3 in planar lipid bilayers.

Voyer, N. Potvin, L. Rousseau, E., (1997) Electrical activity of artificial ion channels incorporated into planar lipid bilayers Perkin Trans. 2, 1469-1471. 

Krasil nikov OV, Sabirov RZ (1992) Comparative analysis of latrotoxin channels of different conductance in planar lipid bilayers. Evidence for cluster organization. Biochim Biophys Acta 1112 124-8... 

Volodkin DV, Michel M, Schaaf P et al (2008) Liposome embedding into polyelectrolyte multilayers a new way to create drug reservoirs at solid-liquid interfaces. In Liu AL (ed) Advances in planar lipid bilayers and hposomes. Elsevier, Amsterdam... 

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