Planar lipid membranes

Figure 13.3 (a-c) Trajectories of the diffusion motion of a gold nanoparticle probe on a planar lipid membrane, (d) Mean-square displacement plots forthe diffusion shown in (a-c). Adapted from Ref [31] with permission. 

Tetraethyllead was used in the past as an antiknock agent in gasoline, but it has been phased out in most countries. Alkyllead compounds have a detergent-like activity on liposomes and black lipid membranes [232], Tributyllead destroys planar lipid membranes at lower concentrations than tripropyllead, which is again more effective than triethyl- and trimethyllead [232]. Inorganic lead compounds like lead acetate and lead nitrate were effective only at twice as high concentrations [232]. 

R. M. Weis, K. Balakrishnan, B. A. Smith, and H. M. McConnell, Stimulation of fluorescence in a small contact region between rat basophil leukemia cells and planar lipid membrane targets by coherent evanescent radiation. J. Biol. Chem. 257, 6440-6445 (1982). 

Scheer H, Prestipino G, Meldolesi J (1986) Reconstitution of the purified a-latrotoxin receptor in liposomes and planar lipid membranes. Clues to the mechanism of toxin action. EMBO J 5 2643-8... 

The design of artificial self-organizing systems is based on the ability of some molecules which contain simultaneously hydrophobic and hydrophilic groups to form molecular assemblies of definite structure in solution. Examples of the assemblies that can be used to suppress undesirable recombination processes are polyelectrolytes, micelles, microemulsions, planar lipid membranes covering an orifice in a film separating two aqueous solutions, unilamellar vesicles, multilamel-lar vesicles and colloids of various inorganic substances (see reviews [8-18] and references therein). 

Could similar channels be produced in the bilayer membranes of primitive cells There is no doubt that channel-like defects appear when a nonpolar peptide interacts with a lipid bilayer. For instance, polyleucine or polyalanine has been induced to fuse with planar lipid membranes, and the bilayers exhibited transient bursts of proton conductance [43]. Surprisingly, channellike conductance also appears when RNA is selected for its ability to bind to phospholipids [44], From these observations it is fair to say that if random polymers were being produced by some unknown synthetic reaction on the early Earth, some of those polymers were likely to have been able to penetrate bilayer membranes and produce channels that bypassed the permeability barrier. This is an area that is ripe for further investigations, as described in a recent review by Pohorille et al. [45]. 

Keywords Lipid bilayer Liposome Lipo-polymer Planar lipid membrane Poly(lipid) Polymerizable lipid Stabilized membrane... 

Crosby DG (1971) Minor insecticides of plant origin. In Jacobson MJ, Crosby DG (eds) Naturally occurring insecticides. Dekker, New York, pp 177-239 Cukierman S (1991) Inactivation modifiers of Na currents and the gating of rat brain Na channels in planar lipid membranes. Pfliigers Arch 419 514-521 Daly JW, Myers CW, Warnick JE, Albuquerque EX (1980) Levels of batrachotoxin and lack of sensitivity to its action in poison-dart frogs (Phyllobates). Science 208 1383-1385... 

The first question concerns the physical nature of such a channel in the F0 subunit. A useful model is provided by the work of Lear et al. (37, 38), who found that synthetic serine-leucine peptides form ion-conducting channels in planar lipid membranes. The channels apparently are produced when a-helical configurations of the peptides form clusters within the bilayer. For instance, when a 21 residue peptide H2N—(LSSLLSL)3—CONH2 was incorporated into a planar lipid bilayer membrane, channels appeared that had cation conducting properties that resembled those of the acetylcholine... 

As described earlier, most of the studies on photocontrolled transport phenomenon focused on azobenzene-doped organic platforms such as planar lipid membranes and spherical vesicles, which have an intrinsic disadvantage. Those lipid membranes and vesicles are delicate and unstable, thus limiting their practical applications. Incorporation of the azobenzene moieties into a robust inorganic matrix greatly enhances the system stability and facilitates the device fabrication. For example, azobenzene moieties precisely positioned onto the pore surfaces of mesoporous silica membranes enable novel photocontrolled transport in the resulting composite materials (Liu et al., 2004). 

Fig. 2 Relationships between current and voltage in a VCH heptameric pore. VCH monomer (10 ng in 5 pi) was added to 2.5 mM N-(2-hydroxyethyl)-piperazine-N -2-ethanes sulfonic acid (HEPES, pH 7.2) with 1 M NaCl in cis-compartment. When one VCH pore was incorporated into the planar lipid membrane, the membrane current was recorded automatically under fluctuating applied membrane potentials (Figure modified from Ref. [6])...

Christensen B, Fink J, Meiriheld RB, Mauterall D. Channel-fonning properties of cecropins and related model compounds incorporated into planar lipid membranes. Proc Natl Acad Sci USA 1988 85 5072-5076. 

The electrical properties of OmpF have been measured for long times, both with patch-clamp techniques and on planar lipid membranes." A high-resolution electrostatic mapping of the trimer was obtained with atomic probe microscopy,while a systematic electrostatic modeling of the pore lumen has been recently performed by two groups who did not limit their study to the wild protein, but comparatively analyzed several mutants. The electrostatic landscape of OmpF is a typical example of how the balance between strong interactions finely tunes the properties of a channel. Ionic trajectories have been simulated both with Brownian and molecular dynamics simulation codes,and the role of ion-ion interaction within the pore has been stressed as being important. 

Robert M. Weis, Krishna Balakrishnan, Barton A. Smith, and Harden M. McConnell, Stimulation of Fluorescence in a Small Contact Region between Rat Basophil Leukemia Cells and Planar Lipid Membrane targets by Coherent Evanescent Radiation , /. Biological Chem., 257,1982, pp 6440-6445. 

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