Membranes planar bilayer

Nanosized supramolecular materials have received increasing attention during the last two decades. Their properties have been surveyed for their ability to form aggregates in the solution phase, which form channel-like arrays in the solid state, and which ultimately form single channels in planar bilayer membranes. These systems therefore illustrate, in general, the convergence of supramolecular selforganization and supramolecular function. 

Figure 4. (a) Planar bilayer membrane system for single-channel currents measurement. Soybean lecithin in n-decane was applied to a hole separating two aqueous chambers. Chambers were filled with metal chloride salt at pH 7.2. The voltage was applied to the outer cell with respect to the inner. The currents across the bilayer were recorded on a PCM recorder through a patch-clamp amplifier and a lowpass filter, (b) Typical records of current observed at -t-50.0 mV (symmetrical 0.5 M solution). Currents increase upward from the zero level shown by the dotted line in each panel. 

When this amphiphile was incorporated into planar bilayer membrane, interesting current behavior was observed the open-closed probabilities varied with the applied voltage. A typical record of the channel current is shown in Figure 22. At 50 mV, the channel is almost closed with only occasional opening. At 70 to 85 mV, the open frequency increases and its duration becomes significantly longer. At 100... 

Benz, R., Janko, K., and Langer, P., Pore formation by the matrix protein (porin) to Escherichia coli in planar bilayer membranes, Ann. N.Y. Acad. Set, 358, 13-24, 1980. 

Ion channels have been purified from several types of excitable cells. The proteins that make up the voltage-gated Na+ channels of brain neurons were first identified by labeling them with reactive derivatives of neurotoxins obtained from scorpions. Intact channels were purified from both brain and muscle after solubilization with detergents. When the purified proteins were incorporated into phospholipid vesicles or planar bilayer membranes, they were found to conduct Na+ across the membrane. The ion specificity of the reconstituted channels and the alterations of the conductance in response to changes in Aift or to various neurotoxins were similar to the properties of the original nerve or muscle membranes. In addition to scorpion toxins, a variety of other specific neurotoxins bind to the purified channels and inhibit their activities. These include tetrodotoxin (a poison obtained from... 

Tozeren, P. K.-L. Sung, L. A. Sung, M. L. Dustin, P. Y. Chan, T. A. Springer, and S. Chien, Micromanipulation of adhesion of a jurkat cell to a planar bilayer-membrane containing lymphocyte function-associated antigen 3 molecules, J. Cell. Biol. 116, 997-1066 (1992). 

PET across membranes is extensively discussed in the first contribution with emphasis on primary photochemical charge separation processes and secondary recombination reactions. Mainly vesicles and planar bilayer membranes serve as models which allow the spatial separation of photochemically generated oxidants and reductants. 

A new family of crown-ether-based bolaamphiphiles, 21, that aggregate into a previously unknown type of bolaamphisome was prepared by Gokel and coworkers [50]. Evidence was presented on vesicle formation from the aqueous suspension of such bolaform amphiphiles. Several reports describing the synthesis of various macrocyclic models related to archael compounds have also appeared in the literature [51]. Fyles et al. prepared a novel series of asymmetric bis-macrocyclic bolaphiles, 22, and evaluated their transport activities in vesicles and planar bilayer membranes [52]. 

White, S. H. Petersen, D. C. Simon, S. Yafuso, M. "Formation of Planar Bilayer Membranes from Lipid Monolayers. A Critique" Biophysical J. 1976, 16, 481-489. 

This technique essentially comprises two aqueous compartments containing electrolyte connected by a pinhole across which a bilayer of phospholipid molecules is spread. An electrical potential is applied across the bilayer and in the presence of an ionophore the resultant current flowing between the two chambers is measured as a function of time.12 The method is often used to assess the activity of synthetic peptides, and has been used to measure the channel activity of several non-peptide channels. Of particular significance is its use in allowing the measurement of the single channel properties of isolated channel-forming proteins that have been reintroduced back into planar bilayer membranes.13... 

Another well-defined synthetic membrane is a planar bilayer membrane. This structure can be formed across a 1-mm hole in a partition between two aqueous compartments by dipping a fine paintbmsh into a membrane-forming solution, such as phosphatidyl choline in decane. The tip of the brush is then stroked across a hole (1 mm in diameter) in a partition between two aqueous media. The lipid film across the hole thins spontaneously into a lipid bilayer. The electrical conduction properties of this macroscopic bilayer membrane are readily studied by inserting electrodes into each aqueous compartment (Figure 12.14). For example, its permeability to ions is determined by measuring the current across the membrane as a function of the applied voltage. 

Figure 12.14. Experimental Arrangement for the Study of Planar Bilayer Membrane. A bilayer membrane is formed across a 1-mm hole in a septum that separates two aqueous compartments. This arrangement permits measurements of the permeability and electrical conductance of lipid bilayers.

Figure 3. Schematic diagram of an apparatus for measuring transmembrane oxidation-reduction in a planar bilayer membrane. The mechanism described is simple carrier-mediated electron transport. D = aqueous electron donor A = aqueous electron acceptor ...

Strong evidence exists for electron hopping in photoinduced transmembrane redox reactions mediated by Ceo and C70 fullerenes across planar bilayer membranes... 

Photoinduced electron transfer across planar bilayer membranes doped with discrete cofacially stacked porphyrin trimers and tetramers has been demonstrated... 

Figure 12.14 Experimental arrangement for the study of a planar bilayer membrane.

Figure 4. Multistate conductance shown by alamethicin on a planar bilayer membrane with applied potential of 210 mV (top) and on frog sarcolemmal membrane with — 110-mV resting potential (bottom). Current bursts begin at A and continue until B. The different levels observed are not integral multiples of unit current conductance, which implies different states of the pore. (Upper figure reproduced with permission from reference 41. Copyright 1972 Elsevier. Lower figure reproduced with permission from reference 302. Copyright 1979 Macmillan Magazines.)...

Planar bilayer membranes were formed from solutions of 25 mg of glycerolmonooleate (Sigma Chemical) in 0.9 mL of decane (Wiley). In both chambers, 0.1-M solutions of thallous acetate (TlAc) with a trace of TlCl were... 

Table III. Four Observed (20) Outcomes for an Planar Bilayer Membrane Oxidized Cholesterol...

Figure 1A. Short time scale (0-1 pus) behavior of the transmembrane voltage [U(t)] predicted by a recent version of the theoretical model for a planar bilayer membrane exposed to a single very short (0.4-fis) pulse that is, charge injection conditions (16). The key features of reversible electrical breakdown (REB) are predicted by the model, as is the occurrence of incomplete reversible electrical breakdown. In the case of incomplete reversible electrical breakdown, the membrane discharge is incomplete because U(t) does not reach zero after the pulse. Each curve is labeled by the corresponding value of the injected charge Q. The curves for Q = 25 and 20 nC show REB, whereas the other...

Figure 2A. Longer time scale (0-80 /is) electrical behavior, predicted by the same model that shows rupture and simple charging of an artificial planar bilayer membrane (16). The characteristic sigmoidal behavior of U(t) is predicted by the model (16), but the time scale is somewhat shorter than found in experiments (61). Each curve is labeled by the corresponding value of the injected charge Q. The curves for Q — 25 and 20 nC are the spikes at t — 0. The curve for Q = 15 nC shows that the membrane underwent REB at t = 2 pus, but the membrane recovered before it had time to discharge completely. The curve for Q = 10 nC shows rupture, whereas the curve for Q = 5 nC shows that the membrane conductance did not increase enough to discharge the...

Figure 5. Theoretical estimate of the transport of propidium iodide (Pi) across an artificial planar bilayer membrane. The molecule was treated as a circular disk with charge zs = +2. Only transient aqueous pores are used in this version of the model Future versions should include metastable pores and estimates of the contributions of diffusion and convection.

Outline the methods used to prepare lipid vesicles (liposomes) and planar bilayer membranes. Point out some applications of these systems. 

A specific interaction was observed between the ganglioside (1), which had been incorporated in glycerol monoleate planar bilayer membranes, and folli-tropin. A five-fold increase in conductance was measured in the presence of (1) while neither di- or tri-sialogangliosides showed any effect. The increase was suppressed by the presence of an equimolar mixture of D-galactose, 2-acetamido-2-deoxy-D-galactose, and iV-acetylneuraminic acid. The results favour the hypothesis that gangliosides may contribute to the formation of functional glycoprotein receptors. 

Fyles, T.M. Looek. D. Van Straaten-Nijenhius, W.F. Zhou, X. Pores formed by his-macrocyclic bola-amphi-philes in vescile and planar bilayer membranes. J. Org. Chem. 1996, 61, 8866-8874. 

To understand the role of pluronics as membrane permea-bilizers, the transport of various small molecules across PC lipid bilayers in the presence of pluronics was examined. To measure the transport of weak acids across planar bilayer membranes (spread over a perforated polytetrafluoroethylene (PTFE) sheet), the corresponding shifts in pH were observed. The addition of pluronic was shown to drastically increase the rate of the weak acid 2-n-undecyl malonic acid transport across the bilayer (Figure 3). This effect increased with increasing concentration of pluronic. This effect was present, though slower, when the pluronic was added to the opposite side of the bilayer from the acid. There were also similar, but far less pronounced, effects on the transport of acetic acid and ammonium. The authors observed that a voltage jump aaoss the membrane in the presence of tetraphenyl borate (TPB ) ion introduced an exponentially decaying current as the ions moved aaoss the membrane. Similar to the pH measurements, the current decay curve in the presence of pluronics showed that TPB" transport occurs much faster in the presence of... 

Freeman, S.A., Wang, M.A., Weaver, J.C., 1994. Theory of electroporation of planar bilayer membranes ... 

---