Surface tension lipid bilayers

It follows from Eqs. (73) and (74) that the only stabilizing force for a-modes at long X is the membrane tension, and critical voltage vanishes as cr 0. In experiments with black lipid membranes the surface tension a arises from the contact of the bilayer with the bulk phase contained in the surrounding rim and is typically < 0.002 N/m. Then choosing... 

For lipid bilayers, equation (4) can be simplified. Above we have seen that the flat unsupported bilayer is without tension, i.e. y(0, 0) = 0, and therefore the first two terms must cancel y0 = — kcj. As argued above, JQ = 0, and thus also the third term drops out. The remaining two terms are proportional to the curvature to the power two. For a cylindrical geometry only, the term proportional to J2 is present. For spherical vesicles, the two combine into one ( kc + k)J2. The curvature energy of a homogeneously curved bilayer is found by integrating the surface tension over the available area ... 

Figure 20. (a) The (dimensionless) lateral compressibility (dilatational modulus, elastic area expansion modulus) (left ordinate) and the dimensionless area per molecule (right ordinate) as a function of the tail length (t) of the PC lipids in equilibrium bilayer membranes. The conversion to real compressibilities and areas per molecule is discussed in the text, (b) The (dimensionless) surface tension and the (dimensionless) lateral compressibility as a function of the relative expansion for the C PC lipid... 

Lindahl, E. and Edholm, O. (2000). Spatial and energetic-entropic decomposition of surface tension in lipid bilayers from molecular dynamics simulations, J. Chem. Phys., 113, 3882-3893. 

Feller, S. E. and Pastor, R. W. (1999). Constant surface tension simulations of lipid bilayers the sensitivity of surface areas and compressibilities, J. Chem. Phys., Ill, 1281-1287. 

Chiu, S. W., Clark, M., Balaji, V., Subramaniam, S., Scott, H. L. and Jakobsson, E. (1995). Incorporation of surface tension into molecular dynamics simulation of an interface a fluid phase lipid bilayer membrane, Biophys. J., 69,1230-1245. 

The results on formation and stability of black foam films, on the first place those on bilayer foam films (NBF) (see Sections 3.4.1.2 and 3.4.4) have promoted the development of methods which enable lung maturity evaluation. The research on stability of amphiphile bilayers and probability for their observation in the grey foam films laid the grounds of the method for assessment of foetal lung maturity created by Exerowa et al. [20,24]. Cordova et al. [25] named it Exerowa Black Film Method. It involves formation of films from amniotic fluid to which 47% ethanol and 7-10 2 mol dm 3 NaCl are added [20,24]. In the presence of alcohol the surface tension of the solution is 29 mN m 1 and the adsorption of proteins from the amniotic fluid at the solution/air interface is suppressed, while that of phospholipids predominates. On introducing alcohol, the CMC increases [26], so that the phospholipids are present also as monomers in the solution. The electrolyte reduces the electrostatic disjoining pressure thus providing formation of black foam lipid films (see Sections 3.4.1.2 and 3.4.4). 

More highly saturated lipids can be used to replace Egg PC. It is well known that increased saturation of the constituent lipids increases the rigidity of lipid monolayers and bilayers and reduces their permeability to small molecules, and increases their ability to resist the compressive effects of surface tension (13, 14). 

As is well known, the bilayer structure of cell manbranes exhibits hydrophobic properties in the hydrocarbon part. This means that those molecules that must interact with the membrane interior must be hydrophobic. Anesthesia is brought about by the interaction between some suitable molecule and the lipid molecules in the biological membrane at the cell interface. The effect of pressure has been reported to be due to the volume change of membranes, which reverses the anesthesia effect. Local anesthetics are basically amphiphile molecules of tertiary amines, and some have colloidal properties in aqueous solution. The anesthetic power is determined by the hydrophobic part of the molecule. Surface tension measurements showed a correlation with the anesthetic power for a variety of molecules dibucane < tetracainebupivacainemepivacaine < lidocaine < procaine (aU as HCl salts). ... 

Information about fluidity and viscosity of bilayers of artificial and natural membranes has been obtained from electron spin resonance studies in which the mobility of the spin-labelled species along the surface plane of the membrane is determined (17). However, the monolayer of either lipid, protein, or lipid-protein systems at the air-water interface, makes an ideal model because several parameters can be measured simultaneously. Surface tension, surface pressure, surface potential, surface viscosity, surface fluorescence and microviscosities, surface radioactivity, and spectroscopy may be determined on the same film. Moreover, the films can be picked up on grids from which they may be observed by electron microscopy, studied further for composition, and analyzed for structure by x-ray diffraction and spectroscopy. This approach can provide a clear understanding of the function and morphology of the lipid and lipid-protein surfaces of experimental membranes. However, the first objective is to obtain molecular correlations of surface tension, pressure, potential, and viscosity. 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the lipids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

The existence of a cortical tension suggests that there is a cortex — a relatively thick layer of F-actin filaments and myosin — that is capable of exerting a finite tension at the surface. If such a layer exists, it would have a finite thickness and bending rigidity. Zhelev et al. [1994] aspirated the surface of neutrophils into pipettes with increasingly smaller diameters and determined that the surface had a bending modulus of about 1 to 2 X 10 J, which is 5 to 50 times the bending moduli for erythrocyte or lipid bilayer membranes. The thickness of the cortex should be smaller than the radius of smallest pipette used in this study, which was 0.24 fjtra. 

Protein first came into the model as a result of considerations of interfacial tension. Danielli and Davson (1934/5) pointed out that measured interfacial tension at lipid-water interfaces was much higher than that evident at cell surfaces. Therefore they put forward a new model in which the lipid bilayer was encased in a sandwich of protein, thereby avoiding this problem and accommodating the protein known to be present in membranes. Thirty years later, the basic premise upon which protein was added to the model was shown to be incorrect (Haydon and Taylor, 1963) phospholipids have interfacial... 

The Helfrich Hamiltonian, Eq. (1), does not include a surface tension contribution. Free membrane patches can relax and adjust their area such that they are stress-free. In many situations, however, membranes do experience mechanical stress. For example, an osmotic pressure difference between the inside and the outside of a lipid vesicle generates stress in the vesicle membrane. Stress also occurs in supported bilayer systems, or in model membranes patched to a frame. In contrast to other quantities discussed earlier (bending stiffness etc.), and also in contrast to the surface tension of demixed fluid phases, membrane stress is not a material parameter. Rather, it is akin to a (mechanical or thermodynamic) control parameter, which can be imposed through boundary conditions. 

Watson MC, Morriss-Andrews A, Welch PM, Brown FLH (2013) Thermal lluctuatimis in shape, thickness, and molecular orientation in lipid bilayers II finite surface tensions. J Chem... 

Jahnig F (1996) What is the surface tension of a lipid bilayer membrane Biophys J 71 1348-1349... 

On our experimental model that signified the formation of a cylindrical membrane tube. By increasing the pressure in the outside section it could be made to collapse with the formation of two planar bilayers. Thus the cycle is completed and can be repeated endlessly. The theory of the collapse of the membrane tube made it possible to develop a new method for measuring surface tension, which is particularly promising for dry membranes. The performance of the entire cycle of fusion with membranes formed from the lipids with a different molecular geometry (i.e. different spontaneous curvature of bilayers) make it possible to prove[37] the Justice of the stalk mechanism. 

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