Journal articles on the topic 'Bilayer shape changes'
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1
Evans, E., and A. Yeung. "Hidden dynamics in rapid changes of bilayer shape." Chemistry and Physics of Lipids 73, no. 1-2 (September 1994): 39–56. http://dx.doi.org/10.1016/0009-3084(94)90173-2.
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Häckl, W., M. Bärmann, and E. Sackmann. "Shape Changes of Self-Assembled Actin Bilayer Composite Membranes." Physical Review Letters 80, no. 8 (February 23, 1998): 1786–89. http://dx.doi.org/10.1103/physrevlett.80.1786.
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Fyles, T. M., D. Loock, and X. Zhou. "Ion channels based on bis-macrocyclic bolaamphiphiles: effects of hydrophobic substitutions." Canadian Journal of Chemistry 76, no. 7 (July 1, 1998): 1015–26. http://dx.doi.org/10.1139/v98-097.
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Four new bis-macrocyclic bolaamphiphiles were prepared to explore the effects of hydrophobic substitutions on ion transport. In bilayer vesicles the new compounds were remarkably similar to more hydrophilic derivatives prepared previously. Planar bilayer conductance experiments showed the new compounds induced an unique current-time signal consisting of a rapid rise time, followed by a slower decay time. Signal shape was cation dependent and was related to a modest selectivity between cations. Cation-anion selectivity was very high, approaching an ideal cation selectivity. One compound also showed voltage dependence of the signal shape and duration. Qualitative changes in signal shape, duration, and voltage dependence were provoked by variation in the electrolyte pH and by masking the head-group electrostatic interactions with low levels of barium ions. A model for the signal shape is proposed, involving a rapid current rise due to aggregate restructuring, followed by slower decay due to development of the local Donnan potential that results from the high cation-anion selectivity.Key words: ion channel, synthesis, bilayer membrane, bilayer clamp, mechanism.
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Hueck, I. S., H. G. Hollweg, G. W. Schmid-Schönbein, and G. M. Artmann. "Chlorpromazine modulates the morphological macro- and microstructure of endothelial cells." American Journal of Physiology-Cell Physiology 278, no. 5 (May 1, 2000): C873—C878. http://dx.doi.org/10.1152/ajpcell.2000.278.5.c873.
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Chlorpromazine (CP), an amphipathic, antipsychotic agent, causes concave membrane bending in red blood cells with formation of stomatocytic shapes by modulation of the phospholipid bilayer. This study was designed to investigate the effects of CP on the shape of bovine aortic endothelial cells (BAEC) and their membranes in confluent monolayers with phase-contrast and transmission electron microscopy. Exposure of BAECs to nanomolar levels of CP leads to membrane curvature changes. With increasing CP concentrations, the membrane assumed a shape with enhanced numbers of intracellular caveolae and projection of pseudopodia at all junctions. At higher CP concentrations (up to 150 μM), the endothelial cells assumed almost spherical shapes. The evidence suggests that CP may affect lipid bilayer bending of BAECs in analogy with previous observations on erythrocytes, supporting the formation of caveolae and pseudopodia in BAECs due to the induction of concave membrane bending, as well as an effect on endothelial cell membrane adhesion at higher CP concentrations with loss of cellular attachment at junctions.
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Redman, CM, T. Huima, E. Robbins, S. Lee, and WL Marsh. "Effect of phosphatidylserine on the shape of McLeod red cell acanthocytes." Blood 74, no. 5 (October 1, 1989): 1826–35. http://dx.doi.org/10.1182/blood.v74.5.1826.1826.
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Abstract The rare McLeod blood group phenotype is characterized by weak Kell antigens, lack of the common Kx antigen, and acanthocytic morphology. Previous studies that did not detect membrane or cytoskeletal protein abnormalities suggested a lipid disturbance. In normal red cells, dimyristoyl phosphatidylserine (DMPS) is transported across the membrane by an enzymatic process and accumulates in the inner leaflet of the membrane bilayer causing discocyte to stomatocyte shape changes. Scanning electron microscopy of McLeod red cells shows a mixture comprised of 15% discocytes, 51% with irregular surfaces, and 34% acanthocytes. On incubation with various concentrations of DMPS at 37 degrees C for periods up to two hours, McLeod red cells transported DMPS across the membrane and caused irregularly shaped and acanthocytic McLeod red cells to attain normal discocyte shape and later to become stomatocytes. Chlorpromazine, which at 0 degrees C preferentially partitions into the inner monolayer of the membrane, had a similar effect on the shape of McLeod red cells. This suggests that in McLeod cells acanthocytosis is due to a lack of lipid in the inner leaflet of the membrane bilayer but that the imbalance is not caused by defective transport of phosphatidylserine across the membrane.
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Redman, CM, T. Huima, E. Robbins, S. Lee, and WL Marsh. "Effect of phosphatidylserine on the shape of McLeod red cell acanthocytes." Blood 74, no. 5 (October 1, 1989): 1826–35. http://dx.doi.org/10.1182/blood.v74.5.1826.bloodjournal7451826.
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The rare McLeod blood group phenotype is characterized by weak Kell antigens, lack of the common Kx antigen, and acanthocytic morphology. Previous studies that did not detect membrane or cytoskeletal protein abnormalities suggested a lipid disturbance. In normal red cells, dimyristoyl phosphatidylserine (DMPS) is transported across the membrane by an enzymatic process and accumulates in the inner leaflet of the membrane bilayer causing discocyte to stomatocyte shape changes. Scanning electron microscopy of McLeod red cells shows a mixture comprised of 15% discocytes, 51% with irregular surfaces, and 34% acanthocytes. On incubation with various concentrations of DMPS at 37 degrees C for periods up to two hours, McLeod red cells transported DMPS across the membrane and caused irregularly shaped and acanthocytic McLeod red cells to attain normal discocyte shape and later to become stomatocytes. Chlorpromazine, which at 0 degrees C preferentially partitions into the inner monolayer of the membrane, had a similar effect on the shape of McLeod red cells. This suggests that in McLeod cells acanthocytosis is due to a lack of lipid in the inner leaflet of the membrane bilayer but that the imbalance is not caused by defective transport of phosphatidylserine across the membrane.
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Krapež Tomec, Daša, Aleš Straže, Andreas Haider, and Mirko Kariž. "Hygromorphic Response Dynamics of 3D-Printed Wood-PLA Composite Bilayer Actuators." Polymers 13, no. 19 (September 22, 2021): 3209. http://dx.doi.org/10.3390/polym13193209.
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The use of wood particles in wood-plastic composites (WPC) is well known and similar use could occur in materials for fused deposition modeling (FDM) 3D printing. Wood particles could be one of the possible solutions in the search for natural-based materials to minimize the use of synthetic-origin materials in additive manufacturing. Wood particles for 3D printing filaments can be made from wood waste and could serve as a cheap filler or as a value-added reinforcing component, depending on their properties and incorporation. The disadvantages of wood (dimensional changes due to water adsorption and desorption) could be used as functions when dimensional change is desirable, such as in shape-changing 4D printing materials. In this research, FDM printing materials made of polylactic acid (PLA), with different amounts of wood particles, were used to design moisture-induced shape-changing bilayer actuators, which could serve as a principle for active façade or ventilation valves. The initial research shows that the wood content in the WPC causes dimensional changes and thus shape changes of the designed actuators under changing climates. The shape change depends on the ratio of the materials in the two-layered actuator and the wood content in the wood-PLA composite used, and thus on sorption. The rate of the shape change behaves in the same way: the higher the wood content, the greater the change observed. The dynamics of the hygromorphism of bimaterial composites is greater with a small amount of added hygromechanically active material.
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Pazukha, I. M., D. O. Shuliarenko, S. R. Dolgov-Gordiichuk, and L. V. Odnodvorets. "Magnetoresistive Properties of Multilayer Film Systems Based on Permalloy and Silver." Physics and Chemistry of Solid State 22, no. 1 (March 27, 2021): 175–79. http://dx.doi.org/10.15330/pcss.22.1.175-179.
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In this paper, the experimental investigation focuses on the magnetoresistive properties of nanosized film systems. Their structure changes from layered to granular due to transition from bilayer FM/NM (FM is a ferromagnetic material, NM is a nonmagnetic material) to [FM/NM]n multilayer film at a constant total thickness of samples. As ferromagnetic and nonmagnetic materials were chosen permalloy Ni80Fe20 (Py) and Ag, respectively. It was demonstrated that the shape of the field dependences of magnetoresistance depends on the number of bilayer Py/Ag. For as-deposited [Py/Ag]n/S at n = 8, 16, the transition from the antiferromagnetic ordering of magnetic moments to ferromagnetic one occurs under an external magnetic field. As a result, the resistivity of the samples reduced, and the giant magnetoresistive effect was realized. The increase of the number of bilayers repeats from 2 to 16 at the unchanged total thickness of the system leads to the growth of the magnetoresistance from 0.1 % to 0.35 %. During annealing up to 600 K, the magnetoresistive effect is reduced, but it does not disappear completely
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Backman, L. "Shape control in the human red cell." Journal of Cell Science 80, no. 1 (February 1, 1986): 281–98. http://dx.doi.org/10.1242/jcs.80.1.281.
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When the human red cell consumes its ATP, the cell loses its discoid character in favour of a spiculated and eventually a spherical form. This discocyte-echinocyte transformation parallels both degradation of phosphatidylinositol 4,5-bisphosphate and phosphatidic acid but not dephosphorylation of cytoskeletal proteins. Dephosphorylation of both spectrin and band 3 lags behind metabolic crenation. Exogenous vanadate accelerates both shape changes and lipid dephosphorylation in a parallel manner during metabolic depletion. In contrast to its effect on lipids, vanadate reduces the rate of protein dephosphorylation. These observations strongly support a shape control mechanism in the red cell, based on phosphoinositide metabolism and compatible with a bilayer-couple model.
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Barns, Sarah, Emilie Sauret, Suvash Saha, Robert Flower, and Yuan Tong Gu. "Two-Layer Red Blood Cell Membrane Model Using the Discrete Element Method." Applied Mechanics and Materials 846 (July 2016): 270–75. http://dx.doi.org/10.4028/www.scientific.net/amm.846.270.
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The red blood cell (RBC) membrane consists of a lipid bilayer and spectrin-based cytoskeleton, which enclose haemoglobin-rich fluid. Numerical models of RBCs typically integrate the two membrane components into a single layer, preventing investigation of bilayer-cytoskeleton interaction. To address this constraint, a new RBC model which considers the bilayer and cytoskeleton separately is developed using the discrete element method (DEM). This is completed in 2D as a proof-of-concept, with an extension to 3D planned in the future. Resting RBC morphology predicted by the two-layer model is compared to an equivalent and well-established composite (one-layer) model with excellent agreement for critical cell dimensions. A parametric study is performed where area reduction ratio and spring constants are varied. It is found that predicted resting geometry is relatively insensitive to changes in spring stiffness, but a shape variation is observed for reduction ratio changes as expected.
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Tharad, Sudarat, Öykü Üzülmez, Boonhiang Promdonkoy, and José Toca-Herrera. "Cholesterol Increases Lipid Binding Rate and Changes Binding Behavior of Bacillus thuringiensis Cytolytic Protein." International Journal of Molecular Sciences 19, no. 12 (November 30, 2018): 3819. http://dx.doi.org/10.3390/ijms19123819.
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Cytolytic protein (Cyt) is a member of insecticidal proteins produced by Bacillus thuringiensis. Cyt protein has activity against insect cells and mammalian cells, which differ in lipid and cholesterol composition. This study presents the lipid binding behavior of Cyt2Aa2 protein on model membranes containing different levels of cholesterol content by combining Quartz Crystal Microbalance with Dissipation (QCM-D) and Atomic Force Microscopy (AFM). QCM-D results revealed that cholesterol enhances the binding rate of Cyt2Aa2 protein onto lipid bilayers. In addition, the thicker lipid bilayer was observed for the highest cholesterol content. These results were confirmed by AFM. The analysis of protein surface coverage as a function of time showed a slower process for 5:0 and 5:0.2 (POPC:Chol) ratios than for 5:1 and 5:2 (POPC:Chol) ratios. Significantly, the Cyt2Aa2-lipid binding behavior and the protein–lipid layer were different for the 5:3 (POPC:Chol) ratio. Furthermore, AFM images revealed a transformation of Cyt2Aa2/lipid layer structure from strip pattern to ring shape structures (which showed a strong repulsion with AFM tip). In summary, cholesterol increases the binding rate and alters the lipid binding behavior of Cyt2Aa2 protein, although it is not required for Cyt2Aa2 protein binding onto lipid bilayers.
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Polychronidou, Maria, Andrea Hellwig, and Jörg Grosshans. "Farnesylated Nuclear Proteins Kugelkern and Lamin Dm0 Affect Nuclear Morphology by Directly Interacting with the Nuclear Membrane." Molecular Biology of the Cell 21, no. 19 (October 2010): 3409–20. http://dx.doi.org/10.1091/mbc.e10-03-0230.
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Nuclear shape changes are observed during a variety of developmental processes, pathological conditions, and ageing. The mechanisms underlying nuclear shape changes in the above-mentioned situations have mostly remained unclear. To address the molecular mechanism behind nuclear shape changes, we analyzed how the farnesylated nuclear envelope proteins Kugelkern and lamin Dm0 affect the structure of the nuclear membrane. We found that Kugelkern and lamin Dm0 affect nuclear shape without requiring filament formation or the presence of a classical nuclear lamina. We also could show that the two proteins do not depend on a group of selected inner nuclear membrane proteins for their localization to the nuclear envelope. Surprisingly, we found that farnesylated Kugelkern and lamin Dm0 protein constructs change the morphology of protein-free liposomes. Based on these findings, we propose that farnesylated proteins of the nuclear membrane induce nuclear shape changes by being asymmetrically inserted into the phospholipid bilayer via their farnesylated C-terminal part.
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Boley, J. William, Wim M. van Rees, Charles Lissandrello, Mark N. Horenstein, Ryan L. Truby, Arda Kotikian, Jennifer A. Lewis, and L. Mahadevan. "Shape-shifting structured lattices via multimaterial 4D printing." Proceedings of the National Academy of Sciences 116, no. 42 (October 2, 2019): 20856–62. http://dx.doi.org/10.1073/pnas.1908806116.
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Shape-morphing structured materials have the ability to transform a range of applications. However, their design and fabrication remain challenging due to the difficulty of controlling the underlying metric tensor in space and time. Here, we exploit a combination of multiple materials, geometry, and 4-dimensional (4D) printing to create structured heterogeneous lattices that overcome this problem. Our printable inks are composed of elastomeric matrices with tunable cross-link density and anisotropic filler that enable precise control of their elastic modulus (E) and coefficient of thermal expansion (α). The inks are printed in the form of lattices with curved bilayer ribs whose geometry is individually programmed to achieve local control over the metric tensor. For independent control of extrinsic curvature, we created multiplexed bilayer ribs composed of 4 materials, which enables us to encode a wide range of 3-dimensional (3D) shape changes in response to temperature. As exemplars, we designed and printed planar lattices that morph into frequency-shifting antennae and a human face, demonstrating functionality and geometric complexity, respectively. Our inverse geometric design and multimaterial 4D printing method can be readily extended to other stimuli-responsive materials and different 2-dimensional (2D) and 3D cell designs to create scalable, reversible, shape-shifting structures with unprecedented complexity.
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Petrova, Valentina A., Daniil D. Chernyakov, Daria N. Poshina, Iosif V. Gofman, Dmitry P. Romanov, Alexander I. Mishanin, Alexey S. Golovkin, and Yury A. Skorik. "Electrospun Bilayer Chitosan/Hyaluronan Material and Its Compatibility with Mesenchymal Stem Cells." Materials 12, no. 12 (June 24, 2019): 2016. http://dx.doi.org/10.3390/ma12122016.
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A bilayer nonwoven material for tissue regeneration was prepared from chitosan (CS) and hyaluronic acid (HA) by needleless electrospinning wherein 10–15 wt% (with respect to polysaccharide) polyethylene oxide was added as spinning starter. A fiber morphology study confirmed the material’s uniform defect-free structure. The roughness of the bilayer material was in the range of 1.5–3 μm, which is favorable for cell growth. Electrospinning resulted in the higher orientation of the polymer structure compared with that of corresponding films, and this finding may be related to the orientation of the polymer chains during the spinning process. These structural changes increased the intermolecular interactions. Thus, despite a high swelling degree of 1.4–2.8 g/g, the bilayer matrix maintained its shape due to the large quantity of polyelectrolyte contacts between the chains of oppositely charged polymers. The porosity of the bilayer CS–HA nonwoven material was twice lower, while the Young’s modulus and break stress were twice higher than that of a CS monolayer scaffold. Therefore, during the electrospinning of the second layer, HA may have penetrated into the pores of the CS layer, thereby increasing the polyelectrolyte contacts between the two polymers. The bilayer CS–HA scaffold exhibited good compatibility with mesenchymal stem cells. This characteristic makes the developed material promising for tissue engineering applications.
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Christiansson, A., F. A. Kuypers, B. Roelofsen, J. A. Op den Kamp, and L. L. van Deenen. "Lipid molecular shape affects erythrocyte morphology: a study involving replacement of native phosphatidylcholine with different species followed by treatment of cells with sphingomyelinase C or phospholipase A2." Journal of Cell Biology 101, no. 4 (October 1, 1985): 1455–62. http://dx.doi.org/10.1083/jcb.101.4.1455.
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In a previous report it was shown that the replacement of native erythrocyte phosphatidylcholine (PC) with different PC species which have defined acyl chain compositions can lead to morphological changes (Kuypers, F.A., W. Berendsen, B. Roelofsen, J. A. F. Op den Kamp, and L.L.M. van Deenen, 1984, J. Cell Biol., 99:2260-2267). It was proposed that differences in molecular shape between the introduced PC species and normal erythrocyte PC caused the membrane to bend outwards or inwards, depending on the shape of the PC exchanged. To support this proposal, two requirements would have to be fulfilled: the exchange reaction would take place only with the outer lipid monolayer of the erythrocyte, and the extent of lipid transbilayer movement would be restricted. If this theory is correct, any treatment causing unilateral changes in lipid molecular shape should lead to predictable morphological changes. Since this hypothesis is a refinement of the coupled bilayer hypothesis, but so far lacks experimental support, we have sought other means to change lipid molecular shape unilaterally. Shape changes of human erythrocytes were induced by the replacement of native PC by various PC species using a phosphatidylcholine-specific transfer protein: by hydrolysis of phospholipids in intact cells using sphingomyelinase C or phospholipase A2, and by the combination of both procedures. The morphological changes were predictable; additive when both treatments were applied, and explicable on the basis of the geometry of the lipid molecules involved. The results strongly support the notion that lipid molecular shape affects erythrocyte morphology.
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Pamplona, D. C., and C. R. Calladine. "The Mechanics of Axially Symmetric Liposomes." Journal of Biomechanical Engineering 115, no. 2 (May 1, 1993): 149–59. http://dx.doi.org/10.1115/1.2894115.
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Hotani has filmed morphological transformations in unilamellar liposomes, starting from a spherical shape, when the interior volume decreases steadily. Hotani’s liposomes showed no evidence of general thermal fluctuations. We use a finite-deformation theory of axisymmetric, quasi-static thin shells to analyze theoretically bifurcations and changes of shape in liposomes under decreasing volume. The main structural action in a lipid bilayer is generally agreed to be its elastic resistance to bending, and it is usual to regard surface deformation as being like that of a two-dimensional liquid. We find, however, that some in-plane shear elasticity is also needed in order to produce the observed post-bifurcation behavior. Such an elasticity would be difficult to measure directly.
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Matthews, Luke, Vishnu Baba Sundaresan, Victor Giurgiutiu, and Donald J. Leo. "Bioenergetics and mechanical actuation analysis with membrane transport experiments for use in biomimetic nastic structures." Journal of Materials Research 21, no. 8 (August 1, 2006): 2058–67. http://dx.doi.org/10.1557/jmr.2006.0250.
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Nastic structures are synthetic constructs capable of controllable deformation and shape change similar to plant motility, designed to imitate the biological process of nastic movement found in plants. This paper considers the mechanics and bioenergetics of a prototype nastic structure system consisting of an array of cylindrical microhydraulic actuators embedded in a polymeric plate. Non-uniform expansion/contraction of the actuators in the array may yield an overall shape change resulting in structural morphing. Actuator expansion/contraction is achieved through pressure changes produced by active transport across a bilayer membrane. The active transport process relies on ion-channel proteins that pump sucrose and water molecules across a plasma membrane against the pressure gradient. The energy required by this process is supplied by the hydrolysis of adenosine triphosphate. After reviewing the biochemistry and bioenergetics of the active transport process, the paper presents an analysis of the microhydraulic actuator mechanics predicting the resulting displacement and output energy. Experimental demonstration of fluid transport through a protein transporter follows this discussion. The bilayer membrane is formed from 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L-Serine] (Sodium Salt), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine lipids to support the AtSUT4 H+-sucrose cotransporter.
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Molotkovsky, Galimzyanov, Batishchev, and Akimov. "The Effect of Transmembrane Protein Shape on Surrounding Lipid Domain Formation by Wetting." Biomolecules 9, no. 11 (November 12, 2019): 729. http://dx.doi.org/10.3390/biom9110729.
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Signal transduction through cellular membranes requires the highly specific and coordinated work of specialized proteins. Proper functioning of these proteins is provided by an interplay between them and the lipid environment. Liquid-ordered lipid domains are believed to be important players here, however, it is still unclear whether conditions for a phase separation required for lipid domain formation exist in cellular membranes. Moreover, membrane leaflets are compositionally asymmetric, that could be an obstacle for the formation of symmetric domains spanning the lipid bilayer. We theoretically show that the presence of protein in the membrane leads to the formation of a stable liquid-ordered lipid phase around it by the mechanism of protein wetting by lipids, even in the absence of conditions necessary for the global phase separation in the membrane. Moreover, we show that protein shape plays a crucial role in this process, and protein conformational rearrangement can lead to changes in the size and characteristics of surrounding lipid domains.
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Haris, Muhammad, Najma Baseer, Yasar Mehmood Yousafzai, Sobia Haris, Usman Naeem, Rabail Rabail, Farah Deeba, and Muhammad Jehangir Khan. "Cytoskeletal changes in Erythrocytes during storage in banked blood." Rehman Journal of Health Sciences 2, no. 2 (February 9, 2021): 64–71. http://dx.doi.org/10.52442/rjhs.v2i2.74.
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Introduction: Erythrocytes have flexible, non-nucleated bi-concave shape with lipid bilayer cytoskeleton. Any alterations of erythrocyte shape make it susceptible to hemolysis. Blood for transfusion purpose is routinely stored in Citrate Phosphate Dextrose Adenine (CPDA-1) containing blood bags. During storage, blood undergoes an array of different morphological changes termed as “storage lesions” which makes it more fragile. This study was aimed to determine the structural and functional modifications in erythrocytes in CPDA-1 blood stored in local blood bank of KPK. Material & Methods: Blood from twenty healthy volunteer donors was taken and kept in CPDA-1 containing blood bags at Institute of Basic Medical Sciences (IBMS), Khyber Medical University (KMU). Hb-levels and Erythrocyte, Reticulocyte counts, Mechanical Fragility Index (MFI) and immunofluorescence staining for ankiyrin1 protein were performed on fresh blood samples. Samples for reticulocyte count was taken for 5 consecutive days while for the remaining parameters, blood was taken at 5 days interval till day 20th. The light and fluorescence micrographs were obtained accordingly and osmotic fragility tests were performed. Results: A significant mean reduction in erythrocyte counts and Hb-level was observed from day 0 to 20 (p=0.001), while MFI increased from day 0 to day 20 (12.88%±7.58 p=0.001). Reticulocyte count also decreased from day 0 up to day 5 (p=0.001). A weak association was observed between changes in MFI and erythrocyte morphology from day 0 to 20 (r=0.349), while the intensity and pattern of ankyrin1 protein expression appeared to change from day 10. Conclusion: Blood stored for a week has same properties as fresh blood, however, important structural alterations start to appear after the first week of storage and worsen with time. Therefore, to gain better transfusion results, blood stored for up to one week can safely be transfused.
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Simon, Kailene S., Naomi L. Pollock, and Sarah C. Lee. "Membrane protein nanoparticles: the shape of things to come." Biochemical Society Transactions 46, no. 6 (November 21, 2018): 1495–504. http://dx.doi.org/10.1042/bst20180139.
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The use of styrene–maleic acid (SMA) for the purification of a wide range of membrane proteins (MPs) from both prokaryotic and eukaryotic sources has begun to make an impact in the field of MP biology. This method is growing in popularity as a means to purify and thoroughly investigate the structure and function of MPs and biological membranes. The amphiphilic SMA copolymer can effectively extract MPs directly from a native lipid bilayer to form discs ∼10 nm in diameter. The resulting lipid particles, or styrene–maleic acid lipid particles (SMALPs), contain SMA, protein and membrane lipid. MPs purified in SMALPs are able to retain their native structure and, in many cases, functional activity, and growing evidence suggests that MPs purified using SMA have enhanced thermal stability compared with detergent-purified proteins. The SMALP method is versatile and is compatible with a wide range of cell types across taxonomic domains. It can readily be adapted to replace detergent in many protein purification methods, often with only minor changes made to the existing protocol. Moreover, biophysical analysis and structural determination may now be a possibility for many large, unstable MPs. Here, we review recent advances in the area of SMALP purification and how it is affecting the field of MP biology, critically assess recent progress made with this method, address some of the associated technical challenges which may remain unresolved and discuss opportunities for exploiting SMALPs to expand our understanding of structural and functional properties of MPs.
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Ruggeri, Francesco, Curtis Marcott, Simone Dinarelli, Giovanni Longo, Marco Girasole, Giovanni Dietler, and Tuomas Knowles. "Identification of Oxidative Stress in Red Blood Cells with Nanoscale Chemical Resolution by Infrared Nanospectroscopy." International Journal of Molecular Sciences 19, no. 9 (August 30, 2018): 2582. http://dx.doi.org/10.3390/ijms19092582.
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During their lifespan, Red blood cells (RBC), due to their inability to self-replicate, undergo an ageing degradation phenomenon. This pathway, both in vitro and in vivo, consists of a series of chemical and morphological modifications, which include deviation from the biconcave cellular shape, oxidative stress, membrane peroxidation, lipid content decrease and uncoupling of the membrane-skeleton from the lipid bilayer. Here, we use the capabilities of atomic force microscopy based infrared nanospectroscopy (AFM-IR) to study and correlate, with nanoscale resolution, the morphological and chemical modifications that occur during the natural degradation of RBCs at the subcellular level. By using the tip of an AFM to detect the photothermal expansion of RBCs, it is possible to obtain nearly two orders of magnitude higher spatial resolution IR spectra, and absorbance images than can be obtained on diffraction-limited commercial Fourier-transform Infrared (FT-IR) microscopes. Using this approach, we demonstrate that we can identify localized sites of oxidative stress and membrane peroxidation on individual RBC, before the occurrence of neat morphological changes in the cellular shape.
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Yang, Ying, Jun-Jie Song, Ming-Wei Wan, Liang-Hui Gao, and Wei-Hai Fang. "Morphologies of self-assembled gold nanorod-surfactant-lipid complexes at molecular level." Acta Physica Sinica 69, no. 24 (2020): 248701. http://dx.doi.org/10.7498/aps.69.20200979.
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Gold nanorods (GNRs) have aroused the extensive interest of many researchers in recent years due to their unique physicochemical properties. However, the toxic cetyltrimethylammonium bromide (CTAB) is often introduced into the process of synthesizing GNRs, which hinders the wide-range applications of GNRs in clinical practice. To reduce the toxicity, the CTAB molecules coated on the surface of GNRs should be replaced by nontoxic and biocompatible agents such as phospholipid. Thus the component and morphology of the mixed coating agents on the surface of GNRs affect the physicochemical properties of GNRs. To study the morphology and properties of the coated GNRs at a molecular level, we investigate the self-assembly of GNRs, CTAB, and dimyristoyl phosphatidylcholine (DMPC) by using solvent-free dissipative particle dynamics simulations. Our results show that the morphology of the assembled complex mainly depends on the CTAB/DMPC molar ratio, while neither of the interaction strength between GNRs and the coating agents nor the diameter of GNRs has significant effect on the morphology. At a certain combination of GNRs-coating agent interaction strength with GNRs diameter, the mixture of CTAB and DMPC on the surface of GNRs undergoes a gradual change in morphology as the CTAB/DMPC molar ratio increases, including the forming of intact bilayer membrane, cracked bilayer membrane, long patches of micelles, and short wormlike micelles winding GNRs in spiral shape. The morphology of intact bilayer membrane verifies the experimental guess, while the other three morphologies are brand-new discoveries. We also find that when the GNR’s diameter becomes smaller, or the CTAB/DMPC molar ratio is larger, or the interaction strength is greater, the agents cap the ends of GNRs, meanwhile the membrane thickness becomes thinner. The multiple morphologies of the assembled complexes can be qualitatively explained by the shape energy of a membrane adsorbed on a solid surface. When the surface tension of the membrane (which is proportional to the spontaneous curvature of the membrane) exceeds a critical value (which is equal to the adhesion energy density of the membrane), the membrane dissociates from the solid surface and its shape changes. The change trend is related to the spontaneous curvature of the free membrane. As a result of the synergy and competition among the inherent curvatures of GNRs, the spontaneous curvature of CTAB/DMPC membrane or micelle, as well as the adhesion energy, various interesting morphologies are produced. Our simulations and analyses directly characterize the morphological structures of CTAB and lipid coated GNRs, which allow us to in depth understand the self-assembling behaviors of GNRs at a molecular level. This is also conductive to achieving the controlled assemblies of GNRs.
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Pamplona, D. "Transformation of Liposomes: Mechanical Behavior and Stability." Applied Mechanics Reviews 46, no. 11S (November 1, 1993): S289—S294. http://dx.doi.org/10.1115/1.3122647.
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Liposomes are small artificial vesicles of lipid bilayer, wich enclose and are surrounded by water. Morphological transformations in liposomes, starting from a spherical shape, due to changes in the osmotic pressure, have been described in the literature. The first transformation is into a circular biconcave form, afterwards the biconcave side view is maintained, while the front view reveals transformations into elliptical or regular polygonal forms, usually triangular, square or pentagonal. Finite elasticity and the theory of thin shells were used to analyse the behavior of the liposomes under decreasing volume. The biological membrane was considered as a two dimensional fluid layer, exhibiting solid properties to some extent, e.g., elasticity. The stability of the liposmes was studied by using the method of elastic perturbation to obtain the critical pressure for the biconcave transformation and the long liposome tubes. The transformations to elliptical and regular polygonal forms were studied using the linear stability equations of elasticity.
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FLÖRKE, Ralf-Rudiger, Kerstin SCHNAITH, Waltraud PASSLACK, Marc WICHERT, Lothar KUEHN, Marlies FABRY, Matthias FEDERWISCH, and Hans REINAUER. "Hormone-triggered conformational changes within the insulin-receptor ectodomain: requirement for transmembrane anchors." Biochemical Journal 360, no. 1 (November 8, 2001): 189–98. http://dx.doi.org/10.1042/bj3600189.
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Interaction between two αβ half-receptors within the (αβ)2 holoreceptor complex is required for insulin binding with high affinity and for insulin-triggered changes of size and shape. To understand the underlying structure–function relationship, two truncated receptor constructs have been characterized. Reduction in the Stokes radius and increase in the sedimentation coefficient, which are characteristic for wild-type receptors, were entirely lacking for the recombinant human insulin receptor (HIR) ectodomain (HIR-ED). Stokes radii of about 5.8nm and sedimentation coefficients of 10.2S were found for both insulin-bound and free HIR-EDs. However, attaching the membrane anchors to the ectodomain, as with the recombinant membrane-anchored ectodomain (HIR-MAED) construct, was sufficient to restore not only high-affinity hormone binding but also the marked insulin-inducible alterations in hydrodynamic properties. The Stokes radii of HIR-MAED complexes, as assessed by non-denaturing PAGE, decreased upon insulin binding from 9.5nm to 7.9nm. In parallel, the sedimentation coefficient was increased from 9.0S to 9.8S. CD and fluorescence spectroscopy of HIR-MAED revealed only minor insulin-induced changes in the secondary structure. Similarity with wild-type receptors has also been demonstrated by the differential insertion of insulin-bound and free HIR-MAED complexes into artificial bilayer membranes of Triton X-114. The results are consistent with a model of receptor function that ensures a global insulin-triggered reorientation of subdomains within the ectodomain moieties while the secondary structure is essentially retained. For the rearrangement of such subdomains, the transmembrane anchors confer essential structural constraints on the receptor ectodomain.
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Lanza, Frarnçois, Alain Beretz, Martial Kubina, and Jean-Pierre Cazenave. "Increased Aggregation and Secretion Responses of Human Platelets when Loaded with the Calcium Fluorescent Probes Quin2 and Fura-2." Thrombosis and Haemostasis 58, no. 02 (1987): 737–43. http://dx.doi.org/10.1055/s-0038-1645981.
Full textAbstract:
SummaryIncorporation into human platelets of the calcium fluorescent indicators quin2 or fura-2 at low concentrations used to measure intracellular free calcium leads to the potentiation of the effects of agonists on platelets. This was shown by increased aggregatory and secretory responses of quin2 or fura-2 loaded platelets after stimulation with ADP, PAP and with low concentrations of thrombin, collagen, the endoperoxide analog U-46619 and the calcium ionophore A 23187. Quin2 and fura-2 mediated platelet sensitisation could be due to altered arachidonic acid metabolism since it was inhibited by prior treatment with the cydooxygenase inhibitor acetylsalicylate. In contrast, platelets loaded with higher concentrations of calcium chelators exhibited diminished aggregation responses to all aggregating agents. This latter effect was accompanied by increased fluidity of the platelet plasma membrane bilayer and by the exposure of a new pool of membranes to the outer surface of platelets, as monitored with trimethylammonium- diphenylhexatriene (TMA-DPH) in platelets loaded with the non-fluorescent calcium probe analog MAPT. In contrast, low concentrations of quin2 did not potentiate shape change of platelets activated with ADP. Thus, shape change and aggregation can be influenced separately by intracellular Ca2+ chelators. We conclude that platelet responses are altered by the incorporation of intracellular calcium chelators at concentrations used to monitor intracellular calcium changes.
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Denisov, Ilia G., Yelena V. Grinkova, Mark A. McLean, Tyler Camp, and Stephen G. Sligar. "Midazolam as a Probe for Heterotropic Drug-Drug Interactions Mediated by CYP3A4." Biomolecules 12, no. 6 (June 20, 2022): 853. http://dx.doi.org/10.3390/biom12060853.
Full textAbstract:
Human cytochrome P450 CYP3A4 is involved in the processing of more than 35% of current pharmaceuticals and therefore is responsible for multiple drug-drug interactions (DDI). In order to develop a method for the detection and prediction of the possible involvement of new drug candidates in CYP3A4-mediated DDI, we evaluated the application of midazolam (MDZ) as a probe substrate. MDZ is hydroxylated by CYP3A4 in two positions: 1-hydroxy MDZ formed at lower substrate concentrations, and up to 35% of 4-hydroxy MDZ at high concentrations. The ratio of the formation rates of these two products (the site of metabolism ratio, SOM) was used as a measure of allosteric heterotropic interactions caused by effector molecules using CYP3A4 incorporated in lipid nanodiscs. The extent of the changes in the SOM in the presence of effectors is determined by chemical structure and is concentration-dependent. MD simulations of CYP3A4 in the lipid bilayer suggest that experimental results can be explained by the movement of the F-F’ loop and concomitant changes in the shape and volume of the substrate-binding pocket. As a result of PGS binding at the allosteric site, several residues directly contacting MDZ move away from the substrate molecule, enabling the repositioning of the latter for minor product formation.
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Bell, Damian C., Huan Yao, Renee C. Saenger, John H. Riley, and Steven A. Siegelbaum. "Changes in Local S4 Environment Provide a Voltage-sensing Mechanism for Mammalian Hyperpolarization–activated HCN Channels." Journal of General Physiology 123, no. 1 (December 15, 2003): 5–20. http://dx.doi.org/10.1085/jgp.200308918.
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The positively charged S4 transmembrane segment of voltage-gated channels is thought to function as the voltage sensor by moving charge through the membrane electric field in response to depolarization. Here we studied S4 movements in the mammalian HCN pacemaker channels. Unlike most voltage-gated channel family members that are activated by depolarization, HCN channels are activated by hyperpolarization. We determined the reactivity of the charged sulfhydryl-modifying reagent, MTSET, with substituted cysteine (Cys) residues along the HCN1 S4 segment. Using an HCN1 channel engineered to be MTS resistant except for the chosen S4 Cys substitution, we determined the reactivity of 12 S4 residues to external or internal MTSET application in either the closed or open state of the channel. Cys substitutions in the NH2-terminal half of S4 only reacted with external MTSET; the rates of reactivity were rapid, regardless of whether the channel was open or closed. In contrast, Cys substitutions in the COOH-terminal half of S4 selectively reacted with internal MTSET when the channel was open. In the open state, the boundary between externally and internally accessible residues was remarkably narrow (∼3 residues). This suggests that S4 lies in a water-filled gating canal with a very narrow barrier between the external and internal solutions, similar to depolarization-gated channels. However, the pattern of reactivity is incompatible with either classical gating models, which postulate a large translational or rotational movement of S4 within a gating canal, or with a recent model in which S4 forms a peripheral voltage-sensing paddle (with S3b) that moves within the lipid bilayer (the KvAP model). Rather, we suggest that voltage sensing is due to a rearrangement in transmembrane segments surrounding S4, leading to a collapse of an internal gating canal upon channel closure that alters the shape of the membrane field around a relatively static S4 segment.
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ROTTER, Björn, Yolande KROVIARSKI, Gaël NICOLAS, Didier DHERMY, and Marie-Christine LECOMTE. "alphaII-Spectrin is an in vitro target for caspase-2, and its cleavage is regulated by calmodulin binding." Biochemical Journal 378, no. 1 (February 15, 2004): 161–68. http://dx.doi.org/10.1042/bj20030955.
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The spectrin–actin scaffold underlying the lipid bilayer is considered to participate in cell-shape stabilization and in the organization of specialized membrane subdomains. These structures are dynamic and likely to undergo frequent remodelling during changes in cell shape. Proteolysis of spectrin, which occurs during apoptosis, leads to destabilization of the scaffold. It is also one of the major processes involved in membrane remodelling. Spectrins, the main components of the membrane skeleton, are the targets for two important protease systems: m- and µ-calpains (Ca2+-activated proteases) and caspase-3 (activated during apoptosis). In this paper, we show that caspase-2 also targets spectrin in vitro, and we characterize Ca2+/calmodulin-dependent regulation of spectrin cleavage by caspases. Yeast two-hybrid screening reveals that the large isoform (1/L) of procaspase-2 specifically binds to αII-spectrin, while the short isoform does not. Like caspase-3, caspase-2 cleaves αII-spectrin in vitro at residue Asp-1185. This study emphasizes a role of executioner caspase for caspase-2. We also demonstrated that the executioner caspase-7 but not caspase-6 cleaves spectrin at residue Asp-1185 in vitro. This spectrin cleavage by caspases 2, 3 and 7 is inhibited by the Ca2+-dependent binding of calmodulin to spectrin. In contrast, calmodulin binding enhances spectrin cleavage by calpain at residue Tyr-1176. These results indicate that αII-spectrin cleavage is highly influenced by Ca2+ homoeostasis and calmodulin, which therefore represent potential regulators of the stability and the plasticity of the spectrin-based skeleton.
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Lundbaek, J. A., and O. S. Andersen. "Lysophospholipids modulate channel function by altering the mechanical properties of lipid bilayers." Journal of General Physiology 104, no. 4 (October 1, 1994): 645–73. http://dx.doi.org/10.1085/jgp.104.4.645.
Full textAbstract:
Lipid metabolites, free fatty acids and lysophospholipids, modify the function of membrane proteins including ion channels. Such alterations can occur through signal transduction pathways, but may also result from "direct" effects of the metabolite on the protein. To investigate possible mechanisms for such direct effects, we examined the alterations of gramicidin channel function by lysophospholipids (LPLs): lysophosphatidylcholine (LPC), lysophosphatidylethanolamine (LPE), lysophosphatidylserine (LPS), and lysophosphatidylinositol (LPI). The experiments were done on planar bilayers formed by diphytanoylphosphatidylcholine in n-decane a system where receptor-mediated effects can be excluded. At aqueous concentrations below the critical micelle concentration (CMC), LPLs can increase the dimerization constant for membrane-bound gramicidin up to 500-fold (at 2 microM). The relative potency increases as a function of the size of the polar head group, but does not seem to vary as a function of head group charge. The increased dimerization constant results primarily from an increase in the rate constant for channel formation, which can increase more than 100-fold (in the presence of LPC and LPI), whereas the channel dissociation rate constant decreases only about fivefold. The LPL effect cannot be ascribed to an increased membrane fluidity, which would give rise to an increased channel dissociation rate constant. The ability of LPC to decrease the channel dissociation rate constant varies as a function of channel length (which is always less than the membrane's equilibrium thickness): as the channel length is decreased, the potency of LPC is increased. LPC has no effect on membrane thickness or the surface tension of monolayers at the air/electrolyte interface. The bilayer-forming glycerolmonooleate does not decrease the channel dissociation rate constant. These results show that LPLs alter gramicidin channel function by altering the membrane deformation energy, and that the changes in deformation energy can be related to the molecular "shape" of the membrane-modifying compounds. Similar alterations in the mechanical properties of biological membranes may form a general mechanism by which one can alter membrane protein function.
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Şafak, Mürşide, Mürsel Alper, and Hakan Kockar. "Growth and Characterisation of Electrodeposited Co/Cu Superlattices." Journal of Nanoscience and Nanotechnology 8, no. 2 (February 1, 2008): 854–60. http://dx.doi.org/10.1166/jnn.2008.b242.
Full textAbstract:
Ferromagnetic/non-ferromagnetic Co/Cu superlattices were grown on polycrystalline Titanium (Ti) from a single electrolyte by electrodeposition. Microstructure and magnetoresistance (MR) of the superlattices were investigated as a function of the electrolyte pH as well as the layer thicknesses. Structural characterisation by X-ray diffraction (XRD) showed that the superlattices have face-centred cubic (fcc) structure with a strong (111) texture at the studied pH levels, but the texture degree is affected by the electrolyte pH. The scanning electron microscope (SEM) studies revealed that the superlattices grown at low pH (2.0) have smoother surfaces compared to those grown at high pH (3.0). The superlattices exhibited either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) depending on the Cu layer thickness. The shape of MR curves changes depending on the combination of Co and Cu layer thicknesses. The superlattices with Co layers less than 3 nm and Cu layers less than 2 nm have broad and non-saturating curves, indicating the predominance of a superparamagnetic contribution, possibly due to the discontinuous nature of the ferromagnetic (Co) layer. For superlattices with the same bilayer and total thicknesses, the GMR magnitude decreased as the electrolyte pHincreased. Besides possible structural differences such as the texture degree and the surface roughness, this may arises from the variation in the Cu content of the ferromagnetic layers caused by the electrolyte pH.
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Suwalsky, M., P. Hernández, F. Villena, F. Aguilar, and C. P. Sotomayor. "Interaction of the Anticancer Drug Tamoxifen with the Human Erythrocyte Membrane and Molecular Models." Zeitschrift für Naturforschung C 53, no. 3-4 (April 1, 1998): 182–90. http://dx.doi.org/10.1515/znc-1998-3-407.
Full textAbstract:
Abstract Tamoxifen, Anticancer Drug, Erythrocyte Membrane, Phospholipid Bilayer Tamoxifen is a non steroidal antiestrogen drug extensively used in the prevention and treatment of hormone-dependent breast cancer. To evaluate its perturbing effect upon cell membranes it was made to interact with human erythrocytes and molecular models. These consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and of dimyristoylphospha-tidylethanolamine (DMPE), representative of phospholipids classes located in the outer and inner leaflets of the erythrocyte membrane, respectively. Experiments by fluorescence spectroscopy showed that tamoxifen interacted with DMPC vesicles fluidizing both its polar head and acyl chain regions. These results were confirmed by X-ray diffraction which indi cated that tamoxifen perturbed the same regions of the lipid. However, it did not cause any significant structural perturbation to DMPE bilayers. The examination by electron micro scopy of human erythrocytes incubated with tamoxifen revealed that they changed their normal discoid shape to stomatocytes. According to the bilayer couple hypothesis, this result means that the drug is inserted in the inner leaflet of the erythrocyte membrane. Given the fact that tamoxifen did not interact with DMPE, it is concluded that it interacted with a protein located in the cytoplasmic moiety of the erythrocyte membrane.
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Balizer, Edward, Jeffry Fedderly, Gilbert Lee, Susan Bartyczak, and Willis Mock. "Investigation of microstructural changes in impacted polyurea coatings using small angle X-ray scattering (SAXS)." Powder Diffraction 26, no. 2 (June 2011): 149–54. http://dx.doi.org/10.1154/1.3590738.
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Three polyureas with decreasing soft segment molecular weights of 1000, 650, and a 250/1000 blend were molded onto circular steel plates and then impacted with a high speed (275 m/s) conical-shaped steel cylinder. The polyurea layer of the post mortem bilayers was characterized on a molecular level by small angle synchrotron X-ray scattering (SAXS) at the Advanced Photon Source at the Argonne National Laboratory. Analysis revealed that the hard domains of the polyureas with lower molecular weight soft segments reformed and oriented over a greater area of the coating, thus increasing the polymer strain hardening and resulting in visibly less out of plane bilayer deformation. This agrees with the hypothesis that polymer strain hardening is a mechanism that retards necking failure of the metal plate.
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Shirsand, S. B., G. V. Wadageri, S. A. Raju, and Gopikrishna Kolli. "Formulation and In Vivo Evaluation of Mucoadhesive Buccal Tablets of Carvedilol." International Journal of Pharmaceutical Sciences and Nanotechnology 6, no. 3 (November 30, 2013): 2164–71. http://dx.doi.org/10.37285/ijpsn.2013.6.3.8.
Full textAbstract:
In present study we studied the feasibility of preparing mucoadhesive buccal delivery systems containing carvedilol to improve drug residence time on buccal mucosa and drug dissolution rate, to circumvent the first-pass metabolism and quick drug entry into the systemic circulation. Bilayer buccal tablets of carvedilol prepared using controlled release and mucoadhesive polymers (hydroxypropyl methylcellulose 15 cps, 50 cps, K4M and Carbopol 934p) along with impermeable backing layer (ethyl cellulose). 15 formulations were developed with varying concentrations of polymers. The designed tablets were evaluated for tablet size, shape, in vitro drug release, stability studies, bioavailability studies and drug-excipients interaction (FTIR). Among the 15 formulations, F151 containing hydroxypropyl methylcellulose 15 cps (48% w/w of matrix layer), Carbopol 934p (2% w/w of matrix layer) and mannitol (channeling agent, 34.5% w/w of matrix layer) was found to be promising. Dissolution tests revealed that 84.73% of carvedilol was dissolved from the formulation F151 in 8 h along with satisfactory bio adhesion strength (5.71 g). Bioavailability studies of the promising formulation were compared with that of the oral solution. The percentage relative bioavailability of the buccal tablets was found to be 121.27%. Stability studies, on the promising formulation indicated that there are no significant changes in drug content and in vitro dissolution characteristics (p<0.05). FTIR studies show no evidence of interaction between drug and excipients. It was concluded that mucoadhesive buccal tablets of carvedilol with controlled unidirectional drug release along with satisfactory bioadhesion strength and with sufficient residence time can be successfully developed by direct compression method.
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Shimizu, Hiroshi, Xiaoming Zhang, Jinsong Zhang, Alexey Leontovich, Kaiyin Fei, Li Yan, and Michael P. Sarras. "Epithelial morphogenesis in hydra requires de novo expression of extracellular matrix components and matrix metalloproteinases." Development 129, no. 6 (March 15, 2002): 1521–32. http://dx.doi.org/10.1242/dev.129.6.1521.
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As a member of the phylum Cnidaria, the body wall of hydra is organized as an epithelium bilayer (ectoderm and endoderm) with an intervening extracellular matrix (ECM). Previous studies have established the general molecular structure of hydra ECM and indicate that it is organized as two subepithelial zones that contain basement membrane components such as laminin and a central fibrous zone that contains interstitial matrix components such as a unique type I fibrillar collagen. Because of its simple structure and high regenerative capacity, hydra has been used as a developmental model to study cell-ECM interaction during epithelial morphogenesis. The current study extends previous studies by focusing on the relationship of ECM biogenesis to epithelial morphogenesis in hydra, as monitored during head regeneration or after simple incision of the epithelium. Histological studies indicated that decapitation or incision of the body column resulted in an immediate retraction of the ECM at the wound site followed by a re-fusion of the bilayer within 1 hour. After changes in the morphology of epithelial cells at the regenerating pole, initiation of de novo biogenesis of an ECM began within hours while full reformation of the mature matrix required approximately 2 days. These processes were monitored using probes to three matrix or matrix-associated components: basement membrane-associated hydra laminin β1 chain (HLM-β1), interstitial matrix-associated hydra fibrillar collagen (Hcol-I) and hydra matrix metalloproteinase (HMMP). While upregulation of mRNA for both HLM-β1 and Hcol-I occurred by 3 hours, expression of the former was restricted to the endoderm and expression of the latter was restricted to the ectoderm. Upregulation of HMMP mRNA was also associated with the endoderm and its expression paralleled that for HLM-β1. As monitored by immunofluorescence, HLM-β1 protein first appeared in each of the two subepithelial zones (basal lamina) at about 7 hours, while Hcol-I protein was first observed in the central fibrous zone (interstitial matrix) between 15 and 24 hours. The same temporal and spatial expression pattern for these matrix and matrix-associated components was observed during incision of the body column, thus indicating that these processes are a common feature of the epithelium in hydra. The correlation of loss of the ECM, cell shape changes and subsequent de novo biogenesis of matrix and matrix-associated components were all functionally coupled by antisense experiments in which translation of HLM-β1 and HMMP was blocked and head regeneration was reversibly inhibited. In addition, inhibition of translation of HLM-β1 caused an inhibition in the appearance of Hcol-I into the ECM, thus suggesting that binding of HLM-β1 to the basal plasma membrane of ectodermal cells signaled the subsequent discharge of Hcol-I from this cell layer into the newly forming matrix. Given the early divergence of hydra, these studies point to the fundamental importance of cell-ECM interactions during epithelial morphogenesis.
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Lipowsky, Reinhard. "Remodeling of membrane compartments: some consequences of membrane fluidity." Biological Chemistry 395, no. 3 (March 1, 2014): 253–74. http://dx.doi.org/10.1515/hsz-2013-0244.
Full textAbstract:
Abstract Biological membranes consist of fluid bilayers with many lipid and protein components. This fluidity implies a high flexibility that allows the membranes to attain a large variety of different shapes. One important shape parameter is the spontaneous curvature, which describes the asymmetry between the two leaflets of a bilayer and can be changed by adsorption of ‘particles’ such as ions or proteins from the aqueous phases. Membrane fluidity also implies that the membranes can change their local composition via lateral diffusion and form intramembrane compartments. Two mechanisms for the formation of such compartments can be distinguished: membrane segmentation arising from structured environments and domain formation as a result of phase separation within the membranes. The interplay between these two mechanisms provides a simple and generic explanation for the difficulty to observe phase domains in vivo. Intramembrane domains can form new membrane compartments via budding and tubulation processes. Which of these two processes actually occurs depends on the fluid-elastic properties of the domains, on the adsorption kinetics, and on external constraints arising, e.g., from the osmotic conditions. Vesicles are predicted to unbind from adhesive surfaces via tubulation when the spontaneous curvature of their membranes exceeds a certain threshold value.
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Barakat, Joseph M., and Eric S. G. Shaqfeh. "Stokes flow of vesicles in a circular tube." Journal of Fluid Mechanics 851 (July 30, 2018): 606–35. http://dx.doi.org/10.1017/jfm.2018.533.
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The inertialess motion of lipid-bilayer vesicles flowing through a circular tube is investigated via direct numerical simulation and lubrication theory. A fully three-dimensional boundary integral equation method, previously used to study unbounded and wall-bounded Stokes flows around freely suspended vesicles, is extended to study the hindered mobility of vesicles through conduits of arbitrary cross-section. This study focuses on the motion of a periodic train of vesicles positioned concentrically inside a circular tube, with particular attention given to the effects of tube confinement, vesicle deformation and membrane bending elasticity. When the tube diameter is comparable to the transverse dimension of the vesicle, axisymmetric lubrication theory provides an approximate solution to the full Stokes-flow problem. By combining the present numerical results with a previously reported asymptotic theory (Barakat & Shaqfeh, J. Fluid Mech., vol. 835, 2018, pp. 721–761), useful correlations are developed for the vesicle velocity $U$ and extra pressure drop $\unicode[STIX]{x0394}p^{+}$. When bending elasticity is relatively weak, these correlations are solely functions of the geometry of the system (independent of the imposed flow rate). The prediction of Barakat & Shaqfeh (2018) supplies the correct limiting behaviour of $U$ and $\unicode[STIX]{x0394}p^{+}$ near maximal confinement, whereas the present study extends this result to all regimes of confinement. Vesicle–vesicle interactions, shape transitions induced by symmetry breaking, and unsteadiness introduce quantitative changes to $U$ and $\unicode[STIX]{x0394}p^{+}$. By contrast, membrane bending elasticity can qualitatively affect the hydrodynamics at sufficiently low flow rates. The dependence of $U$ and $\unicode[STIX]{x0394}p^{+}$ on the membrane bending stiffness (relative to a characteristic viscous stress scale) is found to be rather complex. In particular, the competition between viscous forces and bending forces can hinder or enhance the vesicle’s mobility, depending on the geometry and flow conditions.
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Iwamoto, Masayuki, and Shigetoshi Oiki. "Constitutive boost of a K+ channel via inherent bilayer tension and a unique tension-dependent modality." Proceedings of the National Academy of Sciences 115, no. 51 (December 3, 2018): 13117–22. http://dx.doi.org/10.1073/pnas.1812282115.
Full textAbstract:
Molecular mechanisms underlying channel-membrane interplay have been extensively studied. Cholesterol, as a major component of the cell membrane, participates either in specific binding to channels or via modification of membrane physical features. Here, we examined the action of various sterols (cholesterol, epicholesterol, etc.) on a prototypical potassium channel (KcsA). Single-channel current recordings of the KcsA channel were performed in a water-in-oil droplet bilayer (contact bubble bilayer) with a mixed phospholipid composition (azolectin). Upon membrane perfusion of sterols, the activated gate at acidic pH closed immediately, irrespective of the sterol species. During perfusion, we found that the contacting bubbles changed their shapes, indicating alterations in membrane physical features. Absolute bilayer tension was measured according to the principle of surface chemistry, and inherent bilayer tension was ∼5 mN/m. All tested sterols decreased the tension, and the nonspecific sterol action to the channel was likely mediated by the bilayer tension. Purely mechanical manipulation that reduced bilayer tension also closed the gate, whereas the resting channel at neutral pH never activated upon increased tension. Thus, rather than conventional stretch activation, the channel, once ready to activate by acidic pH, changes the open probability through the action of bilayer tension. This constitutes a channel regulating modality by two successive stimuli. In the contact bubble bilayer, inherent bilayer tension was high, and the channel remained boosted. In the cell membrane, resting tension is low, and it is anticipated that the ready-to-activate channel remains closed until bilayer tension reaches a few millinewton/meter during physiological and pathological cellular activities.
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Grönquist, Philippe, Prijanthy Panchadcharam, Dylan Wood, Achim Menges, Markus Rüggeberg, and Falk K. Wittel. "Computational analysis of hygromorphic self-shaping wood gridshell structures." Royal Society Open Science 7, no. 7 (July 2020): 192210. http://dx.doi.org/10.1098/rsos.192210.
Full textAbstract:
Bi-layered composites capable of self-shaping are of increasing relevance to science and engineering. They can be made out of anisotropic materials that are responsive to changes in a state variable, e.g. wood, which swells and shrinks by changes in moisture. When extensive bending is desired, such bilayers are usually designed as cross-ply structures. However, the nature of cross-ply laminates tends to prevent changes of the Gaussian curvature so that a plate-like geometry of the composite will be partly restricted from shaping. Therefore, an effective approach for maximizing bending is to keep the composite in a narrow strip configuration so that Gaussian curvature can remain constant during shaping. This represents a fundamental limitation for many applications where self-shaped double-curved structures could be beneficial, e.g. in timber architecture. In this study, we propose to achieve double-curvature by gridshell configurations of narrow self-shaping wood bilayer strips. Using numerical mechanical simulations, we investigate a parametric phase-space of shaping. Our results show that double curvature can be achieved and that the change in Gaussian curvature is dependent on the system’s geometry. Furthermore, we discuss a novel architectural application potential in the form of self-erecting timber gridshells.
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Liu, Wei, Shijun Zhang, Fancui Meng, and Lida Tang. "Molecular simulation of ibuprofen passing across POPC membrane." Journal of Theoretical and Computational Chemistry 13, no. 04 (June 2014): 1450033. http://dx.doi.org/10.1142/s0219633614500333.
Full textAbstract:
Permeability assessment is an important procedure in the drug development process, and drug partitioning in membrane bilayer is related to permeability. To investigate the pH dependence on drug partitioning, the process of different ionization state of ibuprofen passing across POPC bilayer was studied using molecular dynamics simulation. The results show that both atomic charge scheme and ionization state of the drug affect the value and shape of energy profile when passing across the POPC bilayer. The neutral ibuprofen (ibuprofen under acidic condition) has a much lower energy barrier as compared with the anionic ibuprofen (ibuprofen under basic condition). Meantime, hydrogen bond analysis also certifies that it is easy for neutral ibuprofen to pass from bulk water to bilayer center. Our calculation suggests that the ionization state of ibuprofen may be changed between neutral and anionic state when passing across membrane: it may be ionized outside the membrane and neutralized inside the membrane.
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Quach, Duy-Truong. "MAGNETIC PROPERTIES AND DOMAIN STRUCTURE OF CoFeB/Pd MULTILAYERS WITH PERPENDICULAR MAGNETIC ANISOTROPY." Vietnam Journal of Science and Technology 57, no. 6 (November 20, 2019): 685. http://dx.doi.org/10.15625/2525-2518/57/6/13885.
Full textAbstract:
The magnetic properties and domain structure of (CoFeB/Pd)n (n = 2 – 10) multilayers with perpendicular magnetic anisotropy have been investigated systematically. The study has been carried out by using vibration sample magnetometer (VSM) and magneto-optical Kerr effect (MOKE) microscope. The results show clear changes of magnetic hysteresis and domain structure when increasing the number of bilayer (n) from 2 to 10. With increasing the number of bilayer, the multilayers’ hysteresis loops change from square-shaped to slanted, while domain structures change from circular-like to maze.
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Suwalsky, M., M. A. Espinoza, I. Sánchez, and F. Villena. "X-Ray Studies on Phospholipid Bilayers. XI. Interactions with Chloramphenicol." Zeitschrift für Naturforschung C 46, no. 7-8 (August 1, 1991): 647–55. http://dx.doi.org/10.1515/znc-1991-7-823.
Full textAbstract:
Abstract Chloramphenicol is a widely used antibiotic with low levels of toxicity. However, scanning electron microscopy revealed morphological changes in human erythrocytes when they interacted in vitro with therapeutical concentrations of chloram phenicol. To explain this shape change, a study concerned with the possible interactions of this antibiotic with bilayers built-up of phospholipids located in either side of the red cell membrane was performed by X-ray diffraction. Results indicated that chloramphenicol was unable to perturb in any significant extent the structure of the phospholipids under study. The only noticeable effects were phase transitions produced to dim yristoylphosphatidylethanolamine bilayers.
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Varga, Zoltán, András Wacha, and Attila Bóta. "Osmotic shrinkage of sterically stabilized liposomes as revealed by time-resolved small-angle X-ray scattering." Journal of Applied Crystallography 47, no. 1 (January 8, 2014): 35–40. http://dx.doi.org/10.1107/s1600576713030513.
Full textAbstract:
Time-resolved synchrotron small-angle X-ray scattering (SAXS) was used to study the structural changes during the osmotic shrinkage of a pharmacologically relevant liposomal drug delivery system. Sterically stabilized liposomes (SSLs) with a diameter of 100 nm and composed of hydrogenated soy phosphocholine, cholesterol and distearoyl-phosphoethanolamine-PEG 2000 prepared in a salt-free buffer were mixed with a buffered 0.3 MNaCl solution using a stopped flow apparatus. The changes in the liposome size and the bilayer structure were followed by using SAXS with a time resolution of 20 ms. A linear decrease in liposome size is observed during the first ∼4 s of the osmotic shrinkage, which reveals a water permeability value of 0.215 (15) µm s−1. The change in the size of the liposomes upon the osmotic shrinkage is also confirmed by dynamic light scattering. After this initial step, broad correlation peaks appear on the SAXS curves in theqrange of the bilayer form factor, which indicates the formation of bi- or oligolamellar structures. Freeze-fracture combined with transmission electron microscopy revealed that lens-shaped liposomes are formed during the shrinkage, which account for the appearance of the quasi-Bragg peaks superimposed on the bilayer form factor. On the basis of these observations, it is proposed that the osmotic shrinkage of SSLs is a two-step process: in the initial step, the liposome shrinks in size, while the area/lipid adapts to the decreased surface area, which is then followed by the deformation of the spherical liposomes into lens-shaped vesicles.
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Omeis, Fatima, Zahia Boubegtiten-Fezoua, Ana Filipa Santos Seica, Romain Bernard, Muhammad Haseeb Iqbal, Nicolas Javahiraly, Robrecht M. A. Vergauwe, et al. "Plasmonic Resonant Nanoantennas Induce Changes in the Shape and the Intensity of Infrared Spectra of Phospholipids." Molecules 27, no. 1 (December 23, 2021): 62. http://dx.doi.org/10.3390/molecules27010062.
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Surface enhanced infrared absorption spectroscopic studies (SEIRAS) as a technique to study biological molecules in extremely low concentrations is greatly evolving. In order to use the technique for identification of the structure and interactions of such biological molecules, it is necessary to identify the effects of the plasmonic electric-field enhancement on the spectral signature. In this study the spectral properties of 1,2-Dipalmitoyl-sn-glycero-3 phosphothioethanol (DPPTE) phospholipid immobilized on gold nanoantennas, specifically designed to enhance the vibrational fingerprints of lipid molecules were studied. An AFM study demonstrates an organization of the DPPTE phospholipid in bilayers on the nanoantenna structure. The spectral data were compared to SEIRAS active gold surfaces based on nanoparticles, plain gold and plain substrate (Si) for different temperatures. The shape of the infrared signals, the peak positions and their relative intensities were found to be sensitive to the type of surface and the presence of an enhancement. The strongest shifts in position and intensity were seen for the nanoantennas, and a smaller effect was seen for the DPPTE immobilized on gold nanoparticles. This information is crucial for interpretation of data obtained for biological molecules measured on such structures, for future application in nanodevices for biologically or medically relevant samples.
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Acosta, J. González, Miryam R. Joya, and J. Barba-Ortega. "Neutral donor in a bilayer spherical semiconductor quantum dot." International Journal of Modern Physics B 29, no. 31 (December 2015): 1550228. http://dx.doi.org/10.1142/s0217979215502288.
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The binding energy of bilayer spherical quantum dots (BSQDs) with randomly distributed neutral donor [Formula: see text] is computationally simulated. We analyze the ground state energy by using different potentials of confinement that include changes in its height, transition region and width, considering theoretical development in which the variational procedure takes a trial function as a product of the ground state wavefunction of the uncoupled electron in the heterostructure, with a correlation function that depends only on electron–ion separation. We find that the curves of the binding energy with repulsive layer have additional peaks, whose position and height depend on the configuration of the confinement is chosen at the center of the dot. Additionally, our results include novel curves for the density of [Formula: see text] impurity states for different potentials’ shapes.
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Suwalsky, M., F. Villena, M. Bagnara, and C. P. Sotomayorc. "Interaction of the Antiarrhythmic Drug Procainamide with Phospholipid Bilayers." Zeitschrift für Naturforschung C 50, no. 3-4 (April 1, 1995): 248–56. http://dx.doi.org/10.1515/znc-1995-3-414.
Full textAbstract:
Several hypotheses link the molecular mechanism of action of the antiarrhythmic drugs (AAD) that belong to class I to non-specific interactions with phospholipids sited in the neighborhood of sodium channels in the membrane of the myocardium. Procainamide (PROC ), one of the least lipophilic drugs of this group, was induced to interact with bilayers of dimyristoylphosphatidylcholine (DMPC) and dimirystoylphosphatidylethanolamine (DMPE), liposomes of DMPC and human erythrocytes. The perturbing effects of PROC upon these systems were respectively determined by X-ray diffraction, fluorescence spectroscopy and scanning electron microscopy. It was found that PROC exerted very little effect upon DMPC and DMPE even at such a high concentration as 10 mᴍ . However, at therapeutical plasma concentrations, PROC induced shape changes in vitro to red cells.
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Suwalsky, Mario, Pedro Hernández, Fernando Villena, Felipe Aguilar, and Carlos P. Sotomayor. "The Anticancer Drug Adriamycin Interacts with the Human Erythrocyte Membrane." Zeitschrift für Naturforschung C 54, no. 3-4 (April 1, 1999): 271–77. http://dx.doi.org/10.1515/znc-1999-3-419.
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Abstract Adriamycin, Anticancer Drug, Erythrocyte Membrane, Phospholipid Bilayer Adriamycin is an aminoglycosidic anthracycline antibiotic widely used in the treatment of cancer. Increasing reports point to the involvement of cell membranes in its mechanism of action. The interaction of adriamycin with human erythrocytes was investigated in order to determine the membrane binding sites and the resultant structural perturbation. Electron microscopy revealed that red cells incubated with the therapeutical concentration of the drug in human plasma changed their discoid shape to both stomatocytes and echinocytes. According to the bilayer couple hypothesis, this means that adriamycin was incorporated into either the inner or outer leaflets of the erythrocyte membrane. To explain this unusual result, the drug was incubated with molecular models. One of them consisted of dimyristoylphosphati-dylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) multilayers, representative of phospholipid classes located in the outer and inner leaflets of the erythrocyte membrane, respectively. X-ray diffraction showed that adriamycin interaction perturbed the polar head and acyl chain regions of both lipids. Fluorescence spectroscopy on another model, consisting of DMPC large unilamellar vesicles (LUV), confirmed the X-ray results in that adriamycin fluidized its hydrophobic moiety. It is concluded that adriamycin incorporates into both erythrocyte leaflets affecting its membrane structure.
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Eskelinen, Sinikka. "The kinetics of drug–membrane interactions in human erythrocytes." Canadian Journal of Physiology and Pharmacology 65, no. 12 (December 1, 1987): 2373–78. http://dx.doi.org/10.1139/y87-376.
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The time course of the shape transformations and vesicle release in human erythrocytes caused by lysophosphatidylcholine and chlorpromazine was monitored using a light microscope – video recording technique. The time required for the erythrocytes to reach a stage I echinocytic shape decreased from 4.0 to 2.0 s, when the concentration of the lysophosphatidylcholine solution injected was increased from 1 to 25 μM. The time required to reach stage II decreased from 8.3 to 3.5 s and that required for vesicle release and the formation of stage IV spherocytes decreased from 78.0 to 11.6 s. Correspondingly, the time needed for the formation of stage I stomatocytes decreased from 2.3 to 1.0 s and that for stage II stomatocytes from 3.1 to 2.0 s, when the ambient chlorpromazine concentration was increased from 50 to 200 μM. The kinetics of the shape transformations of the erythrocytes were dependent on the ambient drug concentration. The rate of shape transformations could be predicted from a formula derived for the kinetics of the incorporation of the detergent into the cell membrane, providing that the affinity coefficient and mass transfer coefficient for drugs changed as a function of the free drug concentration. The results give a time scale for the drug–membrane interactions, i.e., the formation of stages I and II for drug–lipid bilayer interactions and the release of vesicles for drug–cytoskeleton interactions.
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Torres-Sánchez, Alejandro, Daniel Millán, and Marino Arroyo. "Modelling fluid deformable surfaces with an emphasis on biological interfaces." Journal of Fluid Mechanics 872 (June 10, 2019): 218–71. http://dx.doi.org/10.1017/jfm.2019.341.
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Fluid deformable surfaces are ubiquitous in cell and tissue biology, including lipid bilayers, the actomyosin cortex or epithelial cell sheets. These interfaces exhibit a complex interplay between elasticity, low Reynolds number interfacial hydrodynamics, chemistry and geometry, and govern important biological processes such as cellular traffic, division, migration or tissue morphogenesis. To address the modelling challenges posed by this class of problems, in which interfacial phenomena tightly interact with the shape and dynamics of the surface, we develop a general continuum mechanics and computational framework for fluid deformable surfaces. The dual solid–fluid nature of fluid deformable surfaces challenges classical Lagrangian or Eulerian descriptions of deforming bodies. Here, we extend the notion of arbitrarily Lagrangian–Eulerian (ALE) formulations, well-established for bulk media, to deforming surfaces. To systematically develop models for fluid deformable surfaces, which consistently treat all couplings between fields and geometry, we follow a nonlinear Onsager formalism according to which the dynamics minimizes a Rayleighian functional where dissipation, power input and energy release rate compete. Finally, we propose new computational methods, which build on Onsager’s formalism and our ALE formulation, to deal with the resulting stiff system of higher-order partial differential equations. We apply our theoretical and computational methodology to classical models for lipid bilayers and the cell cortex. The methods developed here allow us to formulate/simulate these models in their full three-dimensional generality, accounting for finite curvatures and finite shape changes.
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Niu, Dong, Weitao Jiang, Dachao Li, Guoyong Ye, Feng Luo, and Hongzhong Liu. "Reconfigurable shape-morphing flexible surfaces realized by individually addressable photoactuator arrays." Smart Materials and Structures 30, no. 12 (November 12, 2021): 125032. http://dx.doi.org/10.1088/1361-665x/ac3404.
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Abstract Inspired by the impressive shape reconfigurability in natural systems, stimulus-responsive soft materials have been exploited to enable reconfigurable surface changes, relying on controllable deformations inner soft materials and spatiotemporally varying external stimuli. Among these, light stimulus, due to its high degree of spatial and temporal control manner, has been becoming a particularly powerful actuation means. Especially, photothermal shape transformations induced by bilayered structures, combining light absorption layer and an active layer of hydrogels, SMPs (Shape Memory Polymers), and nanocomposites, have provided a facile reconfigurable scheme. Here, we proposed reconfigurable shape-morphing flexible surfaces with individually addressable photoactuators arrays. By adjusting near-infrared radiation intensity and actuators thickness, the deformations of each actuator can be desirably tuned up to 350 μm. Additionally, actuator arrays can be individually photoactuated one by one due to the remote and straightforward control manner, which give rise to distinct surface morphology. Furthermore, multiple actuators are enabled to demonstrate coupled photomechanical actuation, causing broader area surface reconfigurations. Finally, we tried to explore shape-morphing flexible surfaces applications in a deformable mirror prototype with 19 actuator arrays. Based on photomechanical deformation simulation from COMSOL MultiPhysics, surface change capability was preliminarily researched. We envision that our proposed photoactuated deformable mirror will have a significant impact on the novel design in the future deformable mirrors and metasurfaces.
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Schiffmiller, Aviva, Damon Anderson, and Alan Finkelstein. "Ion selectivity of the anthrax toxin channel and its effect on protein translocation." Journal of General Physiology 146, no. 2 (July 13, 2015): 183–92. http://dx.doi.org/10.1085/jgp.201511388.
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Anthrax toxin consists of three ∼85-kD proteins: lethal factor (LF), edema factor (EF), and protective antigen (PA). PA63 (the 63-kD, C-terminal portion of PA) forms heptameric channels ((PA63)7) in planar phospholipid bilayer membranes that enable the translocation of LF and EF across the membrane. These mushroom-shaped channels consist of a globular cap domain and a 14-stranded β-barrel stem domain, with six anionic residues lining the interior of the stem to form rings of negative charges. (PA63)7 channels are highly cation selective, and, here, we investigate the effects on both cation selectivity and protein translocation of mutating each of these anionic residues to a serine. We find that although some of these mutations reduce cation selectivity, selectivity alone does not directly predict the rate of protein translocation; local changes in electrostatic forces must be considered as well.