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The transmembrane distribution of membrane constituents in the two leaflets of a cylindrical bilayer, which is in contact on both sides with an electrolyte solution, was studied by mathematical modeling. The model considers electrostatic interactions between the charged membrane molecules and the monovalent ions of the electrolyte solution, the bending elasticity of the membrane, as well as the anisotropy of the molecular intrinsic shape in the membrane. We showed that the strongly anisotropic uncharged membrane constituents are distributed asymmetrically between the two leaflets of the membrane. The asymmetric transmembrane distribution of charged weakly anisotropic membrane constituents is caused by the difference between the ionic strengths in the outer solutions and those in the inner solutions. For strongly anisotropic charged constituents in the membrane, we found that the asymmetric transmembrane distribution is driven by an interplay between the shape and the charge of the membrane constituents, as well as the difference between the ionic strengths in the outer solutions and those in the inner solutions. We also showed that the composition of the bilayer and the intrinsic curvatures of membrane components influence the stability of the tube.

Polyelectrolyte multilayer sensor capsules, 5 microm in diameter, which contained fluorescein-labeled poly(acrylic acid) (PAAAF) as pH-sensitive reporter molecules, were fabricated and employed to explore their endocytotic uptake into HEK 293T cells by flow cytometry. The percentage of capsules residing in the endolysosomal compartment was estimated from the fluorescence intensity decrease caused by acidification. Capsules attached to the extracellular surface of the plasma membrane were identified by trypan blue quenching. The number of capsules in the cytoplasm was rather small, being below the detection limit of the method. The advantages of polyelectrolyte multilayer capsules are that the fluorophore is protected from interaction with cellular compartments and that the multilayer can be equipped with additional functions.

Asymmetric and porous polysulfone (PSf) membranes were prepared by wet phase separation. Binary (PSf)/N,N-dimethylacetamide (DMA) solutions with polymer concentrations of 12.5–30 wt % were cast in thicknesses of 80–700 μm and immersed in a coagulation bath of pure water. The morphology of the formed membranes' cross sections consisted of a cellular structure and macrovoids; the cellular structure density was highest when the cast solution contained about 21 wt % PSf, regardless of the cast thickness. The membranes' pure water permeability decreased as the cast thickness increased. The instantaneous onset of the turbidity, regardless of the PSf content and cast thickness, its steep growth, and relatively high end value were the main characteristics of the turbidity phenomena taking place during the formation of the protomembranes. Again, the membrane-forming system with a PSf/DMA solution with about 21 wt % polymer, regardless of the cast thickness, had the highest turbidity end value. The shrinkage of the cast solutions into the corresponding protomembrane was also examined quantitatively. Inverse experiments showed that the direction of the gravitation field had no influence on the shrinkage of the membrane-forming ternary system or the membranes' morphology and its water permeability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1667–1674, 2005

The direct accumulation of polymer, the nucleation and growth of the polymer lean as well as the polymer rich phase and the spinodal phase separation are postulated as four elementary processes of the mechanisms of the polymeric membrane formation by wet-phase separation. With the study of five different polymer/solvent:water systems they are discriminated by the investigation of the turbidity and the shrinkage phenomena taking place during (proto)membrane formation, as well as by the measurement of the pure water permeability and by the inspection of the membranes’ cross-section morphology. The general scheme of membrane formation mechanisms is arranged by gathering the groups of different modes of mass transport and the group of nonsolvent/solvent/polymer forms of solidification as elementary processes; by forming combinations of the so postulated elementary processes in time and space particular mechanisms are established.

The time dependent uptake of 1-anilino-8-naphthalene sulphonate (ANS) by bovine erythrocytes was studied. Experimental results were compared with theoretical predictions in order to determine the inner erythrocyte membrane surface potential. The value of the inner membrane surface potential under physiological conditions was estimated as −35 mV. In addition, the number of ANS binding sites on the outer surface of the single bovine erythrocyte membrane was determined as 2.2 × 106.

The action of different agonists such as acetylcholine on the membrane of airway smooth muscle cells may induce cytosolic Ca(2+) oscillations which can be a part of the Ca(2+) signalling pathway, eventually leading to cell contraction. The aim of the present study is to present a mathematical model of the possible effect of the initial Ca(2+) distribution within the cell on the form and frequency of induced Ca(2+) oscillations. It takes into account intracellular Ca(2+) stores such as sarcoplasmic reticulum and cytosolic proteins as well as Ca(2+) exchange across the plasma membrane. We are able to demonstrate a closer agreement of model predictions with observed Ca(2+) traces for a significantly wider range of parameter values, as was previously reported. We show also that the total cellular Ca(2+) content is an important system parameter especially because of the content in sarcoplasmic reticulum. At a total Ca(2+) increase of about 20%, the oscillation frequency increases by 25%; also, damped oscillations become sustained. Cases are indicated in which such a situation could occur.

A mathematical model is presented to simulate transverse lipid movement in the human erythrocyte membrane from one membrane monolayer to the other. The model is based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady-state distribution. Different translocation mechanisms are considered in a combined way. These are the ATP-dependent carrier mediated translocation, the carrier mediated facilitated diffusion and carrier independent transbilayer diffusion. Using realistic values of model parameters the model allows calculation of the transbilayer motion and distribution of phospholipids of the human erythrocyte membrane for several biologically relevant conditions and different experimental conditions.

We report on novel observations on the appearance of macrovoids in the ternary cellulose acetate (CA)/acetone (ACE)/water membrane forming system. The membranes are prepared by the wet phase separation whereby the cast solution is composed of ACE and polymer, and the coagulation bath is pure water only. It is found that the macrovoid formation in a 12.5 wt.% cast solution strongly depends on the cast solution thickness: macrovoids appear at the thickness of 500 μm but not at 150 and 300 μm.

A mathematical model for the dynamics of transbilayer movements of lipids in the erythrocyte plasma membrane is presented. It takes into account an active carrier which mediates the ATP-dependent translocation of phosphatidylserine and phosphatidylethanolamine from the outer to the cytoplasmic leaflet of the membrane and passive fluxes of theses lipids as well as of phosphatidylcholine, sphingomyelin and cholesterol between both layers. It is assumed that the passive fluxes are driven by concentration gradients of the lipids and by mechanical forces which result from area limitation for lipid occupation in both leaflets. Compared with a previous mathematical treatment of lipid translocation processes in the erythrocyte membrane the present model is much closer to realistic conditions, e.g. concerning the number of lipid species involved. Furthermore, the use of linear flux-force relationships as known from irreversible thermodynamics allows a simpler treatment of the passive fluxes than before and provides a relevant framework to study the coupling between the various processes. The model allows to simulate the time dependent changes of lipid concentrations which take place after activation or inhibition of ATP-dependent translocation. Using realistic parameter values it explains in quantitative terms the stationary asymmetric distribution of lipids under in vivo conditions. Using principles of metabolic control analysis we are able to quantify the role of the various active and passive processes in determining the asymmetric distribution for each lipid species.

A model is presented to simulate transverse lipid movement in the human erythrocyte membrane. The model is based on a system of differential equations describing the time-dependence of phospholipid redistribution and the steady state distribution between the inner and outer membrane monolayer. It takes into account several mechanisms of translocation: (i) ATP-dependent transport via the aminophospholipid translocase; (ii) protein-mediated facilitated and (iii) carrier independent transbilayer diffusion. A reasonable modelling of the known lipid asymmetry could only be achieved by introducing mechanism (iii). We have called this pathway the compensatory flux, which is proportional to the gradient of phospholipids between both membrane leaflets. Using realistic model parameters, the model allows the calculation of the transbilayer motion and distribution of endogenous phospholipids of the human erythrocyte membrane for several biologically relevant conditions. Moreover, the model can also be applied to experiments usually performed to assess phospholipid redistribution in biological membranes. Thus, it is possible to simulate transbilayer motion of exogenously added phospholipid analogues in erythrocyte membranes. Those experiments have been carried out here in parallel using spin labeled lipid analogues. The general application of this model to other membrane systems is outlined.

A metabolic osmotic model of red blood cells is presented which takes into account the main reaction steps of glycolysis and the passive and active fluxes of ions across the cell membrane. Cellular energy metabolism and osmotic behaviour are linked by the ATP consumption for the active transport of cations as well as by the osmotic action of the glycolytic intermediate 2,3-diphosphoglycerate (2,3-DPG). The model is based on a system of differential equations describing the metabolic reactions and transport processes. Further, two algebraic conditions for the osmotic equilibrium and the electroneutrality of the cell are considered. Using realistic system parameters the model allows the calculation of a great number of dependent variables, among them the cell volume, the concentrations of metabolites and ions and the transmembrane potential. Only stationary states are considered. The parameter dependence of important model variables is characterized by control coefficients. The main results are: (a) The volume of erythrocytes is mainly determined by the permeabilities of the leak fluxes of cations, the content of hemoglobin and the activity of the hexokinase-phosphofructokinase system of glycolysis; (b) Changes of volume affect the glycolytic rate mainly by changing the concentration of ATP which is a regulator of glycolysis; (c) A change in the membrane area may affect the other cell properties only if it is connected with variations of the number of active and leak sites of the membrane.