Lipid matrices

A state of fluidity and thus of translational mobitity in a membrane may be confined to certain regions of membranes under certain conditions. For example, protein-protein interactions may take place within the plane of the membrane, such that the integral proteins form a rigid matrix—in contrast to the more usual situation, where the hpid acts as the matrix. Such regions of rigid protein matrix can exist side by side in the same membrane with the usual lipid matrix. Gap junctions and tight junctions are clear examples of such side-by-side coexistence of different matrices. 

The Desmopressin diffusion coefficient in the cubic phase at 40 C (D=0.24 x 10-10 m2s-l) is about a factor 9 smaller than in 2H20-solution at 25 C (D=2.25 x 10-10 m s" ), a difference which is larger than what is expected from pure obstruction effects a reduction factor of three is expected from the inclusion of a solute in the water channels of the cubic phase (13). Thus, the results indicate an interaction between the peptide and the lipid matrix and/or membrane surface, especially since the peptide and lipid diffusion coefficients are very similar in the cubic phase (Table... 

The binding of carotenoids within the lipid membranes has two important aspects the incorporation rate into the lipid phase and the carotenoid-lipid miscibility or rather pigment solubility in the lipid matrix. The actual incorporation rates of carotenoids into model lipid membranes depend on several factors, such as, the kind of lipid used to form the membranes, the identity of the carotenoid to be incorporated, initial carotenoid concentration, temperature of the experiment, and to a lesser extent, the technique applied to form model lipid membranes (planar lipid bilayers, liposomes obtained by vortexing, sonication, or extrusion, etc.). For example, the presence of 5 mol% of carotenoid with respect to DPPC, during the formation of multilamellar liposomes, resulted in incorporation of only 72% of the pigment, in the case of zeaxanthin, and 52% in the case of (1-carotene (Socaciu et al., 2000). A decrease in the fluidity of the liposome membranes, by addition of other... 

Skin toxicity is determined by the penetration and transport of the compound being tested through the lipid matrix in the outer skin layers (the stratum corneum)... 

Up to now in this chapter, we have concentrated on the measurement via electric field sensitive dyes of the transmembrane electrical potential, which by itself should produce a linear drop in the electrical potential across a membrane. However, at least through the lipid matrix of a cell membrane, the electrical potential, /, at any point does not change linearly across the membrane. Instead, it follows a complex profile (see Fig. 6). This is due to contributions other than the transmembrane electrical potential to /. The other contributions come from the surface potential and the dipole potential. Both of these can also be quantified via electric field sensitive dyes. 

The solvent evaporation technique is based on the use of organic solvents as dissolving agents for the lipid matrix (i.e., phospholipids or triglycerides and monoglycerides) and the subsequent evaporation of the solvent within an aqueous medium until a CLS dispersion is obtained. 

Concerning the SLN produced by hot homogenization as described by Olbrich et al. [19], as lipidic matrix Compritol ATO 888 or paraffin were used, as tenside a mixture of Tween 80 and Span 85 was used, and as charge carrier either EQ1 [N,N-di-(()-s(eaoryI e(liyI)-.V,A -di methylammonium chloride] or cetylpyridinium chloride were used. The resulting particles were characterized by size between 101 and 105 nm and showed zeta potentials around 40 mV at pH 7.4. 

Muller, R.H., Ruhl, D., Runge, S., Schulze-Forster, K., and Mehnert, W., Cytotoxicity of solid lipid nanoparticles as a function of the lipid matrix and the surfactant, Pharmaceutical Research, 1997, 14, 458-462. 

A representative gas chromatogram with ECD of the analysis of various polar chlorinated pesticides isolated from cod liver oil [179] is shown in Fig. 13. Determination of the polar chlorinated pesticides in cod liver oil required clean up of the lipid matrix with a dimethylformamide/water/hexane liquid-liquid partitioning procedure followed by isolation using a normal-phase LC procedures, and final analysis by GC-ECD [179]. 

Various PCB congeners and lower polarity pesticide fractions analyzed from cod liver oil is shown in Fig. 15 [179]. Measurement of the PCB congeners and pesticides in the cod liver oil required clean-up of the lipid matrix with a di-methylformamide/water/hexane liquid-liquid partitioning procedure followed by isolation of the PCBs and pesticides using a normal-phase LC procedures. The normal-phase LC procedures separate the analytes into two fractions, one containing the PCBs and the lower polarity chlorinated pesticides (HCB, 2,4 -DDE, and 4,4 -DDE) (Fig. 15) and the second containing the more polar chlorinated pesticides. The separation of PCBs and pesticides reduces the possible coelution of many of the pesticides with PCB congeners of interest. These two fractions were then analyzed by GC-ECD. 

R. Lange-Lieckfeldt and G. Lee. Use of a model lipid matrix to demonstrate the dependence of the stratum corneum s barrier properties on its internal geometry. J. Control. Release 20 183-194 (1992). 

Lipid nanodispersions (SLN and NLC) are complex, thermodynamically unstable systems. The colloidal size of the particles alters physical features (e.g., increasing solubihty and the tendency to form supercooled melts). The complex structured lipid matrix may include hquid phases and various lipid modifications that differ in the capacity to incorporate drugs. Lipid molecules of variant modifications may differ in their mobility. Moreover, the high amount of emulsifier used may result in liposome or micelle formation in addition to the nanoparticles. 

Westesen, K. and Bunjes, H., Do nanoparticles prepared from lipids solid at room temperature always possess a solid lipid matrix Int. J. Pharm., 115, 129-31, 1995. 

When preparing lipid nano- and microparticles from solid, crystalline raw materials, it is usually expected that the lipid matrix of the particles is or will become solid after the dispersion step. It has, however, turned out that some matrix materials do not crystallize easily in the colloidally dispersed state after processing in the heat ) 2005 by CRC Press LLC... 

Both the inhaled and the intravenous anesthetics can depress spontaneous and evoked activity of neurons in many regions of the brain. Older concepts of the mechanism of anesthesia evoked nonspecific interactions of these agents with the lipid matrix of the nerve membrane (the so-called Meyer-Overton principle)—interactions that were thought to lead to secondary changes in ion flux. More recently, evidence has accumulated suggesting that the modification of ion currents by anesthetics results from more direct interactions with specific nerve membrane components. The ionic mechanisms involved for different anesthetics may vary, but at clinically relevant concentrations they appear to involve interactions with members of the ligand-gated ion channel family. 

The involvement of lipid membrane constituents in the interaction of ATP with the protein moiety of the calcium transport system emerges if one compares the reaction of ATP with membrane preparations whose lipid matrix has been removed or modified... 

The calcium-independent ATPase of the lipid modified preparations is not only different from the calcium-dependent ATPase but also from the calcium-independent ATPase of native preparations — the basic ATPase — which has a lower nucleotide specificity126. The experiments in which the lipid matrix of the sarcoplasmic membranes has been replaced by lipid compounds not present in native membranes reveal a high degree of functional flexibility of the enzyme. On the other hand, a few residual lipids in the protein are sufficient to prevent these changes in the structure of the enzyme and to preserve its calcium sensitivity. 

Fig. 2, The lipid-globular protein mosaic model with a lipid matrix (fluid mosaic model1) schematic three dimensional and cross-sectional view. The solid bodies with stippled surfaces represent the globular integral proteins, which are randomly distributed in the plane of the membrane...

Biological membranes are always pictured as being very selective barriers separating different biochemical reaction compartments. This high performance transport specificity solely depends on the presence of membrane proteins embedded in the lipid matrix. On the other hand, most membrane proteins cease to function in the absence of lipids. In order to introduce biological transport abilities into artificial membrane systems protein-lipid interactions are of vital interest. The question is how the activity of membrane proteins is affected if they are placed into a polymeric environment. 

Lipid Theories. Although there are many varieties of the lipid theory all postulate that inhalational anesthetics exert their primary effects by dissolving in the lipid portions of nerves, thereby altering the conductivity. The primary site of action is postulated to be the lipid matrix of... 

Membranes contain proteins that merely bind to their surface (peripheral proteins) and those that are embedded in the lipid matrix (integral proteins). Integral membrane proteins contain transmembrane a-helices. 

Receptor Action In Analytical Membranes. This work has Identified the Importance of some of the relevant parameters associated with organized lipid matrix ion conduction. Receptors embedded In these matrices should function to perturb one or more of the three compartmenta 1 zones of the BLM. A number of features significant to electrochemical receptor operation follow ... 

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