Stability Of Bilayer Lipid Membranes Research Articles

Bilayer lipid membranes for flow injection monitoring of acetylcholine, urea, and penicillin.

This work describes a technique for the rapid and sensitive determination of acetylcholine, urea, and penicillin in flowing solution streams using stabilized systems of solventless bilayer lipid membranes (BLMs). This method of monitoring substrates of hydrolytic enzyme reactions made use of BLMs which were supported on ultrafiltration membranes such as polycarbonate and glass microfiber; these filter membranes were found to enhance the stability of BLMs for uses in flow injection experiments. The enzymes were immobilized on BLMs by incorporating the protein solution into the lipid matrix at the air/electrolyte interface before the BLM formation, followed by injections of the substrates into flowing streams of a carrier electrolyte solution. Hydronium ions produced by the enzymatic reaction at the BLM surface caused dynamic alterations of the electrostatic fields and phase structure of BLMs, and as a result ion current transients were obtained; the magnitude of these signals was correlated to the substrate concentration, which could be determined at the micromolar level. The response times were ca. 10 s, and acetylcholine, urea, and penicillin could be determined in continuous flowing systems with a maximum rate of 220 samples/h. It is expected that this analytical utility of stabilized BLMs for flow stream uses will provide new opportunities in this strategy of chemical sensing.

Highly stable bilayer lipid membranes (BLMs) formed on microfabricated polyimide apertures

Microfabrication is used to realize a polyimide aperture for highly stable bilayer lipid membranes (BLMs). The microfabrication process used in this work is compatible with standard processes used in microelectronics. The physical features of the aperture, such as diameter, thickness and tapering of the edges are precisely controlled during the microfabrication process which results in high yield and reproducibility of the polyimide apertures. A study of BLM stability using precise measurements of specific capacitance shows that the BLM is stable up to 50 h. Alamethicin channels were successfully incorporated into these membranes further proving their bilayer nature. Vesicles containing reconstituted nicotinic acetylcholine receptors (nAChRs) were fused to the BLMs. The successful incorporation of functioning ion channel activity into highly stable BLMs promises a future class of miniature sensors that are very sensitive with fast response times.

Influence of dolichyl phosphate on permeability and stability of bilayer lipid membranes

The ionic permeability coefficients, ionic transference numbers, activation energy of ion transport and breakdown voltage of bilayer liquid membranes made from diolcoylphosphatidylcholine or its mixtures with dolichyl 12-phosphate have been studied. The electrical measurements showed that dolichyl phosphate in phospholipid bilayers decreases membrane permeability, changes membrane ionic selectivity and increases membrane stability. These results are discussed in light of the aggregation behavior and the intramolecular clustering of a dolichyl phosphate molecule in phospholipid membranes. From our data we suggest that the hydrophilic part of dolichyl phosphate molecules regulates their behavior in membranes.

Formation and stability of bilayer lipid membrane at a liquid-liquid interface

This paper presents an experimental study on the formation process of ultrathin (500-100 Å in thickness) bilayer liquid membranes at a liquid-liquid interface using oil-soluble chloroplast extract. With the aid of a microvideo system, the dynamics of membrane thinning, border suction, and equilibrium state were visually examined in detail, and the rate of spreading data for the black membrane is analyzed. The effect of salt concentration in aqueous solutions on the bifacial tension is measured over the concentration range of 0.01 to 0.05 N. Reproducibility of these bifacial tension measurements was typically ±21% of the mean value for a particular set of membranes. As an interfacial phenomenon, the formation of ultrathin lipid membranes is investigated in terms of membrane viscosity and bifacial tension. Based on experimental results, a semiquantitative two-step model is proposed for the rate of membrane formation.

Large amplitude photo-voltage transients of bilayer lipid membranes in the presence of chlorophyllin

Large amplitude electrical voltage transients result from the flash illumination of bilayer lipid membranes (BLM) in the presence of chlorophyllin, electron acceptors [FeCl3 or (NH4)2 Ce(NO3)6] and an electron donor (FeCl2). The BLM were prepared from lecithin and oxidized cholesterol, or spinach chloroplast extracts. The photo-voltage waveforms observed may be resolved into three components, which have characteristic times of approximately the flash duration (8 μsec), 1 msec, and the BLM resistance-capacitance discharge time. These components are thus comparable to the Components A, B, and D previously reported for BLM and thin lipid membranes (TLM) of the spinach chloroplast extracts in the presence of electron acceptors. Component C of the chloroplast-BLM is extinguished by near trace quantities (1 μg/l) of chlorophyllin. Higher concentrations (1 to 20 mg/l) reduce the BLM resistance and stability but under some conditions the Component A response exceeds 200 mV. The inferred peak photo-current exceeds 10 mA/cm2. Membrane resistance and stability data suggest that the chlorophyllin bonds within and disrupts the adjacent interface (monolayer), but that it does not permeate the BLM.