Black Lipid Membranes BLMs

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. 

Even closer to cell membranes than monolayers and bilayers are organized surfactant structures called black lipid membranes (BLMs). Their formation is very much like that of an ordinary soap bubble, except that different phases are involved. In a bubble, a thin film of water — stabilized by surfactants — separates two air masses. In BLMs an organic solution of lipid forms a thin film between two portions of aqueous solution. As the film drains and thins, it first shows interference colors but eventually appears black when it reaches bilayer thickness. The actual thickness of the BLM can be monitored optically as a function of experimental conditions. Since these films are relatively unstable, they are generally small in area and may be formed by simply brushing the lipid solution across a pinhole in a partition separating two portions of aqueous solution. 

The phenomena of association colloids in which the limiting structure of a lamellar micelle may be pictured as composed of a bimolecular leaflet are well known. The isolated existence of such a limiting structure as black lipid membranes (BLM) of about two molecules in thickness has been established. The bifacial tension (yh) on several BLM has been measured. Typical values lie slightly above zero to about 6 dynes per cm. The growth of the concept of the bimolecular leaflet membrane model with adsorbed protein monolayers is traceable to the initial experiments at the cell-solution interface. The results of interfacial tension measurements which were essential to the development of the paucimolecular membrane model are discussed in the light of the present bifacial tension data on BLM. 

The electrical properties of black lipid membranes (BLM s) have probably been studied more than those of other lipid systems because of the great similarity between BLM s and cell membranes. The electrical properties of BLM s were reviewed extensively by other authors (32, 33, 34, 35), and we shall therefore describe the electrical and physical properties of lipids which are not generally touched upon in connection with BLM s. We also concentrate on those properties which are intimately related to the different states of order in lipid systems. 

Bilayer (black) lipid membranes, BLMs, are formed by brushing an organic solution of a surfactant (or lipid) across a pinhole (2-4 mm diameter) separating two aqueous phases (15,16). Alternatively, BLMs can be formed from monolayers by the Montal-Mueller method (17,18). In this method, the surfactant, dissolved in an apolar solvent, is spread on the water surface to form a monolayer below the teflon partitioning which contains the pinhole (0.1-0.5 mm diameter). Careful injection of an appropriate electrolyte solution below the surface raises the water level above the pinhole... 

Such relationships can be useful in designing synthetic membranes having properties similar to natural systems. For example, Equation 4 correlates the change in resistance caused by alcohols on potassium ion permeability of black lipid membrane (BLM) prepared from the lipid of sheep erythrocytes. The rather large negative intercept of Equation 4 indicates that three times the concentration of isolipophilic alcohol is needed to change the resistance of the BLM as is needed to cause hemolysis. Although the two processes are quite different, the role of hydrophobic forces in each can be compared. 

Two main methods exist to characterize synthetic ion channels and pores [2], Conductance experiments in planar or black lipid membranes (BLMs) reveal the... 

For lyotropic systems, such as black lipid membranes (BLM), flexoelectric coefficients much larger than those estimated for thermotropic liquid crystals were observed as early as 1973, and were called a peculiar kind of piezoelectric effect . Later Petrov et studied this effect in detail... 

In this way, by measuring Uf and Cm, or //, Co and c, termine experimentally the fiexocoefiicient /. Evaluation of the membrane curvature can be performed electrically from the second harmonic of the membrane capacitance current with a non-zero voltage clamp (the condenser microphone effect) and supposing spherical curvature. The actual curvature c - - C2 of a black lipid membrane (BLM) can be measured interferometrically. " ... 

Fig. 10 Schematic diagram of the voltammetric responses and SECM experiments at a black lipid membrane (BLM) using a K -selective micropipette electrode based on valinomycin. The micropipette electrode is characterized by the electrode radius, a, and rg is the distance from the center to the edge of the pipette. The BLM is located at the distance d. (Reprinted with permission from Ref [66], Copyright 2000 by American Chemical Society.)...

Planar bimolecular lipid membranes, also called black lipid membranes (BLM s) represent a further membrane model system, which is stable only for a few minutes up to several hours. All attempts to further stabilize these BLM s by diyne polymerization failed Diaoetylene compounds which have been studied are listed inTable 5. 

In this chapter, we will review methods to characterize the activity of synthetic transport systems in translocating molecules across otherwise impermeable membranes for beginners in the field. The following two sections briefly introduce methods with bulk membranes (U-tube experiments) and planar or black lipid membranes (BLMs), and close with a more comprehensive overview of methods involving liposomes, in particular large unilamellar vesicles (LUVs). The fourth section will then focus on how to apply... 

Black lipid membrane (BLM) A planar unilamellar bilayer of micrometer extent which appears black in reflected light, used in single-channel conductance transport experiments. Typically the BLM is formed in small opening in a supporting polymer sheet. 

Kimizuka N, Wakiyama T, Yanagi A, Shinkai S, Kunitake T. Calix[4]arene-mediated transport of alkali ions across synthetic black lipid membranes (BLM). Bull Chem Soc 1996 69(12) 3681. ... 

Several works (2,3) have described the ability of an hemocyanin, called Keyhole Limpet Hemocyanin (KLH), to interact with black lipid membranes (BLM) giving rise to the formation of facilitated ionic pathways through the bilayer. 

---