[Membrane type artificial lung--the improved gas exchange capability of the artificial membrane].
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Animals↗
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[Evaluation of interaction between drugs and ordered phospholipid membrane by immobilized artificial membrane chromatography].
AIM: To investigate the interaction between drugs and ordered phospholipid membrane using immobilized artificial membrane chromatography (IAMC). METHODS: IAMC was used to determine the interaction drugs with phospholipid membrane, expressed as membrane affinity (lg kIAM). An n-octanol/buffer system was also employed as the reference hydrophobicity (lg Do/w,7.4). RESULTS: Within the range of used acetonitrile percentages (phi) 0-30% in mobile phase, retention index (lg kIAM) showed excellent correlation with phi. Intercepts of fitted straight lines between lg kIAM and phi were comparable but slopes were much different for the three organic modifiers (acetonitrile, ethanol and methanol). Effects by adding CH2 substituent on lipophilicity difference (delta lg kIAM and delta lg Do/w,7.4) were similar for p-hydroxyl benzoic methyl ester to butyl ester, whereas different for p-hydroxylbenzoic acid to methyl ester. CONCLUSION: IAMC system is a convenient, efficient and rapid tool for determining membrane interaction.
Membranes, Artificial↗
[History and importance of electrically excitable artificial membranes].
Solubility of narcotics in lipids has promoted the quest for non-aqueous and lipidic models of cell membranes. Artificial phosphatidic bilayers have been proposed. They display ionic conductance and excitability only if they are in contact with cyclic ion-carrier or specific substances, such as the protein fraction EIM. However many lipidic substances form non-bilayer membranes ion-conducting and excitable, without any specific additive. Only a small amount of free fatty acid is necessary. This is the condition for penetration through cation exchange. Coloured cations and cationic drugs undergo large exchange. Cu++, Hg++, emetine ++ cations have very high exchange coefficients which can be experimentally measured and which explain their respective antifungal, antibacterial and antiamoebian actions. The possible processes of membrane excitation are discussed. First the classical pores, specific of K+ and Na+ transfers and their "gating" mechanisms, because cell membranes are bi-ionic systems. Artificial membranes, are mono-ionic systems. But recent work shows that the axon membrane can be transformed into a monoionic system with Co++ as the only cations inside and outside the axon. Suggestions for the excitation processes are proposed. a) The assumption of a single energy barrier corresponding to minor conformational changes of structure. b) The membrane may be thixotropic. An outside cation penetrating the membrane would leave behind itself a wake of fluidity into which the next cations could penetrate if they follow each other closely. If they progress widely apart (under a small field), the ionic current would soon stop as the structure solidifies. c) The most promising suggestion is that anionic fixed charges in the membranes and cations form electrostatically bound ion-pairs. Dissociation of such pairs, that is conductance, augments markedly when dielectric constant increases. This process could be produced by water carried by incoming cations, that is by electro osmosis. This is exactly what occurs in Teorell's membrane oscillator in which a model membrane of fritted glass displays, under a weak current, oscillations of water flux and of potentials. The calculations pertaining to this model can be generalised if the electroosmotic water flux is assumed in increase the dielectric constant of the lipidic membrane. Thus the notion of an electroosmotic increase upon the dielectric constant of the membrane offers an alternative to the pore theory. Besides other phenomena show the role of low dielectric constants. The conductance of lipids containing coloured cations increase when subjected to illumination. The radiant energy absorbed then surpasses the association energy of ion pairs.
Animals↗
Serratia marcescens hemolysin (ShlA) binds artificial membranes and forms pores in a receptor-independent manner.
Both the inactive and active conformations of the hemolysin/cytolysin of Serratia marcescens (ShlA) binds membranes of erythrocytes, but only active ShlA is able to form pores. ShlA is unable to lyse prokaryotic membranes. To determine the receptors of the binding and pore-forming domains of active cytolysin on eukaryotic membranes, artificial large unilamellar vesicles (LUVs) of various membrane compositions were examined. In the current study, it is shown that significant pore formation and lysis was achieved with binary phosphatidylcholine/phosphatidylserine (PS) liposomes. No proteinaceous receptor was needed for either binding or pore formation by ShlA. Membrane integration and pore-forming activity were enhanced by addition of phosphatidylethanolamine. Phosphatidylserine is negatively charged at physiologic pH and is almost absent in prokaryotic membranes. Hence, membrane binding and insertion of ShlA are highly dependent on phosphatidylserine, which targets the toxic activity to eukaryotic cell membranes without any need of a proteinaceous receptor. This may explain why prokaryotic membranes were found to be resistant against ShlA in a previous study.
Bacterial Proteins↗
Laboratory feeding of Culicoides impunctatus (Diptera: Ceratopogonidae) through natural and artificial membranes.
An artificial membrane, blood-feeding technique was evaluated for Culicoides impunctatus Goetghebuer using wild-caught insects in Scotland. Chick skins and stretched Nescofilm were satisfactory as feeding membranes. The maximum mean feeding rate achieved was 61.7 +/- 4.0% through Nescofilm with < or = 50 female midges per cage. This rate decreased as a negative function of time and density. A 4 degrees C decrease in blood temperature resulted in a 30% reduction in feeding. ATP applied to the outer membrane surface at 0.01 M and 0.1 M concentrations increased the feeding rate at 30 min after collection from 19.3 +/- 3.3% to 37.2 +/- 4.2% (0.01 M) and 34.5 +/- 4.9% (0.1 M). The Nescofilm membrane method will aid in colonization and may be useful in virus transmission experiments.
Animals↗
[Characteristics of artificial membranes].
The artificial membranes used in haemodialysis and haemofiltration are either cellulosic or made of synthetic polymers, such as polyacrylonitrile, polysulfone, polycarbonate, polymethylmetacrylate and ethyvinylalcohol. During dialysis the water and solute transfer primarily depends on hydraulic permeability and sieving coefficients. At present, high-flux membranes have sieving coefficients for urea (Mol. wt 60) to inulin (Mol. wt 5,200) that are similar to those of the glomerular basal lamina, whereas their hydraulic permeability remains well below that of the renal filter. Bioincompatibility factors responsible for acute, anaphylactoid-like reactions and chronic inflammatory complications have been identified. The choice of the correct dialysis membrane must rest not only on performance criteria but also on biocompatibility and economic criteria.
Biocompatible Materials↗
Solid phase membrane mimetics: immobilized artificial membranes.
The studies discussed demonstrate the importance of developing rapid methods to purify membrane proteins and also quantitate binding events between cell membranes and biomolecules. Traditional equilibrium methods are experimentally very difficult because of long equilibration times, peptide aggregation, and the need to make several measurements to obtain a single binding constant. We are developing chromatographic methods to measure binding constants between membranes and biomolecules by using solid phase membrane mimetics. Solid phase binding assays are well established for reactions that typically occur in solution, whereas for reactions that require a membrane environment, no solid phase assay exists. Solid phase membrane mimetics have the potential of filling this gap.
Membrane Fusion↗
Evaluating interactions of amphoteric molecules with phospholipid membrane using immobilized artificial membrane chromatography.
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Chemical Phenomena↗
Mobile phase effects on membrane protein elution during immobilized artificial membrane chromatography.
The eluotropic strength of different mobile phases for eluting membrane proteins from immobilized artificial membrane (IAM) chromatography surfaces was studied. Two protein mixtures containing bovine pancreatic PLA2 were used in this study. Protein mixture I was PLA2 obtained from Sigma which contained approximately 5-10 major protein bands in electrophoretic gels. Protein mixture II was obtained from flesh bovine pancreatic tissue and contained > 100 proteins including the target protein, PLA2. After adsorbing Sigma PLA2 to IAM columns, the elution conditions common to conventional chromatographic methods were evaluated for their ability to selectively purify PLA2. Elution conditions tested were (i) detergent gradients, (ii) salt gradients used during ion-exchange chromatography, (iii) salt conditions used during hydrophobic interaction chromatography, (iv) acetonitrile gradients used during reversed-phase chromatography, and (v) a two-step gradient consisting of first a detergent gradient followed by an acetonitrile gradient. Based on silver-stained electrophoretic protein gels. PLA2 from protein mixture I was purified to electrophoretic homogeneity with 417-fold increase in specific activity in one step using elution condition (v), and PLA2 from protein mixture II was purified in one step (660-fold increase in specific activity) using elution condition (iv). Total protein recovery from IAM columns is 70-100%.
Animals↗
Immobilized-artificial-membrane chromatography: measurements of membrane partition coefficient and predicting drug membrane permeability.
Immobilized artificial membranes (IAMs) are chromatographic surfaces prepared by covalently immobilizing cell membrane phospholipids to solid surfaces at monolayer densities. IAM surfaces mimic fluid cell membranes. For 23 structurally unrelated compounds, solute capacity factors [log (k'IAM)] measured on IAM columns correlate very well with the solute equilibrium partition coefficients [log (Km)] measured in fluid liposome systems (r = 0.907). This indicates that solute partitioning between the IAM bonded phase and the aqueous mobile phase is similar to the solute partitioning between liposomes and the aqueous phase. IAMs also predicted oral drug absorption in mice and drug permeability through Caco-2 cells. IAM chromatography is experimentally simple and large volume screening of experimental compounds for drug absorption is possible. Solute retention on IAMs was found to be dominated by a partitioning mechanism. The structural requirements for HPLC bonded phases to predict solute-membrane partitioning are briefly discussed.
Adsorption↗
[Immobilized artificial membrane chromatography and its application in profiling the drug membrane transport].
Immobilized artificial membrane chromatography (IAMC) is a system of covalently bonding monolayer of phospholipid analogs onto the solid surface of silica particles, thus establishing the emulating process of drug-cellular membrane interactions in terms of chromatographic method, and is applied to profile the drug membrane permeability and biological activity. IAMC phases prepared from phosphocholine analogues closely mimic the surface of the biological cell membrane, and the capacity factor of drugs can be used to predict the interaction between drug molecules and cell membranes. IAMC, compared with n-octanol/water, liposome/water and ODS chromatography, can simulate other forces besides hydrophobic interaction. IAMC is getting more and more profound research because of its convenience and high efficiency. The primary screening by means of IAMC in the early stage of drug development would effectively lower failure in the preclinical and clinical development, since efficacy and safety are related in the larger part to membrane permeability. The interaction mechanism of drug-IAM and its profiling in membrane transport are reviewed.
Chromatography↗
The promise of the membrane artificial lung.
Membrane lungs are more physiologic than bubble or disc blood oxygenators. Membrane lungs are indispensable in long term perfusions. Recently, there has been a noticeable trend toward use of the membrane lung in open heart surgery. Improper use of the membrane lung lowers its optimum potential and may lead to disenchantment on the part of the user. It is important to recognize that for optimum performance of the membrane lung it is necessary to learn to correctly use the membrane lung.
Artificial Organs↗
ARTMEM--an interactive graphical program simulating membrane potential measurements across artificial membranes.
This paper describes ARTMEM, an interactive graphical simulation program, and its use for teaching students the concept of membrane potentials and the measurement of electrical potentials across an ion-selective membrane. The program, written in Borland C++, and specifically designed for IBM-PC-compatible equipment, can also run on fast Macintosh computers using SoftPC emulation software. It demonstrates how an ion-selective membrane separating two different salt solutions automatically generates a potential across the membrane, as well as how such electrical potentials can be measured simply and the underlying permeability ratio determined. The program was developed to replace a previous experiment with actual artificial resin membranes; virtually every feature of the experiment has been simulated (e.g., unstirred-layer effects, solution-mixing mixing contamination, liquid junction potential effects). In addition, a number of these features and the procedure for data fitting are more clearly demonstrated using the computer simulation. The efficacy of such a simulation is discussed in comparison with the real experiment and other types of simulations.
Computer Graphics↗
Membrane partition coefficients chromatographically measured using immobilized artificial membrane surfaces.
Immobilized artificial membranes (IAMs) are chromatographic surfaces prepared by covalently immobilizing cell membrane phospholipids. IAM surfaces mimic fluid cell membranes. Solute capacity factors (k'IAM) measured on IAM columns correlate very well with solute equilibrium partition coefficients (Km') measured in fluid liposome systems. For 23 structurally unrelated compounds, log-(k'IAM) correlates with log(Km') with a linear correlation coefficient r = 0.907. This indicates that solute partitioning between the IAM bonded phase and the aqueous mobile phase is similar to the solute partitioning between liposomes and the aqueous phase. Although both IAM chromatography and liposome partitioning can be used as in vitro methods to predict solute partitioning into cell membranes, IAM chromatography is experimentally convenient compared to liposome systems. To study the effect of lipid structure on drug binding to IAMs, IAMs were prepared from three different phosphatidylcholine ligands: (i) a diacylated phosphatidylcholine ligand, (ii) a single chain ether phosphatidylcholine ligand, and (iii) a single chain phosphatidylcholine ligand that lacks a glycerol backbone. Solute retention data were identical for all of these IAMs, and consequently, predictions of solute binding to fluid membranes were also identical. This indicates that the structure of the phosphatidylcholine ligand that is immobilized is not critical for the binding of solutes. Since the structure is not important, the binding of solutes to membranes is a bulk phase property, i.e., it is the interface created by the ligands that determines the solute binding properties, not the ligands themselves. Solute partitioning using octanol/water systems does not correlate with k'IAM unless a homologous series of hydrophobic solutes is being evaluated.
Binding Sites↗
Preparation of mixed ligand immobilized artificial membranes for predicting drug binding to membranes.
Mixed ligand immobilized artificial membranes (IAMs) are surfaces that contain at least two immobilized membrane phospholipids which are designated as either the primary phospholipid or the secondary phospholipid. The primary immobilized phospholipid refers to the immobilized phospholipid that has the highest surface density. For this work, the primary immobilized phospholipid was a single-chain ether phosphatidylcholine (PC) analog. Four mixed-ligand IAMs were prepared by use of immobilized PC as the primary immobilized phospholipid. The secondary immobilized phospholipid ligand was either phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, or phosphatidic acid. All of these secondary phospholipids are bonded at approximately 6-10 mol % relative to the molar amount of immobilized PC. Each secondary phospholipid contains functional groups in the polar head group region that require protecting groups during the immobilization process. The four-step synthetic strategy to prepare mixed-ligand IAMs involves (i) immobilization of the PC analog at high density to silica propylamine (SPA), (ii) immobilization of the second phospholipid (PL) analog at low density, (iii) end capping residual amines with a long-chain anhydride followed by end capping with a short-chain anhydride, and (iv) deprotection of the polar head group protecting groups. The surface density of the mixed PLs bonded to the silica support was approximately 130 mumol of PLs/g of SPA. High-performance liquid chromatography using these mixed lipid IAMs can be exploited to rapidly predict the membrane binding properties of drugs.
Adrenergic alpha-Agonists↗
Theoretical comparison of filtration by the renal glomerulus and artificial membranes.
Improvement in filtration performance of artificial membranes will be possible if their structure mimics the renal glomerulus. Blood filtration with glomerular capillary and artificial membranes was, therefore, modeled to clarify the effects of their structure on filtration rates. Filtration rates were obtained by dividing membrane modules axially into a number of sections and using a calculus of finite differences. The modules were assumed to be composed of straight hollow fibers arranged in parallel, with a membrane surface area of 1.5 m2. The mean transmembrane pressure (TMP) was assumed to be too low for a protein gel layer to form on the membrane surface. A decrease in the inner diameter of membrane hollow fibers led to an increase in filtration rate because of an increased film mass transfer coefficient. A decrease in hollow fiber length also produced an increase in filtration rate because of decreased axial TMP drop. The glomerular capillary has a higher filtration rate than artificial membranes because of the low TMP drop and the low osmotic pressure at the membrane surface. Decreasing both the inner diameter and the length of the hollow fibers is effective in increasing the filtration rate at constant TMP.
Blood Flow Velocity↗
Single step purification of rat liver aldolase using immobilized artificial membrane chromatography.
Aldolase B is a peripheral membrane protein. Immobilized artificial membrane (IAM) surfaces were used to purify rat liver aldolase B in a single chromatographic step. Selective elution required dipalmitoylphosphatidylcholine (DPPC) to be included in the mobile phase. Selective elution of aldolase from the IAM column when DPPC (0.2 mM) was added to the mobile phase indicates that DPPC was an affinity displacing ligand for this membrane associated protein. Since tissue preparation involved only homogenization and centrifugation, the single step purification of aldolase B using IAM chromatography is a very convenient method. The IAM stationary phase (1.5 g) has a loading capacity of at least 4.39 mg total protein from rat liver homogenates and typically approximately 17.7 microg of pure aldolase in a single step from approximately 60 mg wet weight rat liver cytosol can be obtained.
Amino Acid Sequence↗
Development and evaluation of an artificial membrane for determination of drug availability.
Various artificial membranes (e.g. PAMPA) and cellular-based membranes (e.g. Caco-2) are used for screening during early stages of drug discovery. However, these methods are not well suited for evaluation of pharmaceutical formulations and the effects of various excipients on drug availability. When drug molecules permeate biological membranes they encounter two types of permeation resistance, a membrane resistance in the lipophilic membrane and diffusion resistance in the unstirred water layers adjacent to both surfaces of the lipophilic membrane. We have developed an artificial membrane that is cheap and simple to prepare. The unstirred water layer consists of a hydrated semi-permeable cellophane membrane with a molecular weight cutoff (MWCO) of 12,000-14,000 Da and a lipophilic membrane of pure n-octanol in a nitrocellulose matrix. In the diffusion cell the hydrated cellophane membrane (thickness 210-230 microm) is on the donor side and the lipophilic octanol membrane (thickness about 120 microm) on the receptor side. Permeation of ionizable lipophilic drug molecules was diffusion-controlled when the drug was unionized but lipophilic membrane controlled when the drug was ionized. Drug permeation patterns from cyclodextrin containing formulations through the membrane were similar to those previously observed for biological membranes such as hairless mouse skin and the eye cornea.
Animals↗