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At least 73 records · Page 4Linked to original sources
PubMed2004

[Effect of bcl-2 over-expression on the membrane structure of NG108-15 nerve cells: effectiveness of membrane-structure analysis using FACS for the first screening of apoptosis-inducing drugs].

Bcl-2 is a Bcl-2 family protein that is known to be anti-apoptotic and is predominantly localized to the mitochondria. We previously showed that an analgesic, buprenorphine hydrochloride (Bph), induces apoptosis in the rodent-derived nerve cell line, NG108-15, through the mitochondrial apoptotic route. A Bcl-2-overexpressing strain of NG108-15 cells, Bcl-2 (P2), was established, and the effect of Bcl-2 expression on Bph-induced apoptosis was compared between the mock vector-transfected NG108-15 cells and the Bcl-2 (P2) cells. The Bcl-2 (P2) cells died after treatment with Bph, and we observed all the biological and morphological markers of apoptosis that we tested for. In flow cytometric analysis, a difference in the cell membrane phospholipid flip-flop pattern-a feature of apoptosis- was observed between the NG108-15 cells and the Bcl-2 (P2) cells. Here, we show by flow cytometric analysis that Bcl-2 over-expression may affect the membrane structure of Bcl-2 (P2) cells. An increased fluorescein isothiocyanate (FITC) signal of annexin V-FITC, which typically represents phospholipid flip-flop of the cellular membrane in early apoptosis, was barely detected in the Bcl-2 (P2) cells. Since our previous study reported the localization of over-expressed Bcl-2 protein to the cell membrane of Bcl-2 (P2) cells, together these observations suggest that the Bcl-2 protein may affect the integrity of the structure of the NG108-15 cell membrane.

Animals↗
PubMedDate not supplied

Intranuclear undulating membranous structures in cells of a human parosteal osteosarcoma.

Large numbers of paracrystalline undulating membranous structures (UMS) were observed in the nuclei of dense cells in a human parosteal osteosarcoma. The electron-dense walls of the structures were 15-20 nm thick, and circular profiles had an outer diameter of 60-70 nm and an inner diameter of 25-30 nm. The UMS-containing cell nuclei displayed a number of other characteristic features, including vermicellar bodies, large numbers of interchromatin granules, and prominent perichromatin granules. The possible significance of these features is discussed.

Adult↗
PubMed2001

L-carnitine modifies the humoral immune response in mice after in vitro or in vivo treatment.

Although the role of L-carnitine (L-Cn) as a cofactor in the oxidation of long-chain fatty acids has been well established, this agent has also been recognized to have an important role in the regulation of carbohydrate metabolism, and consequently, the maintenance of cell membrane structure and cell viability. L-Cn has been reported to reduce the apoptotic levels of CD4+ and CD8+ cells. It has also been demonstrated to interfere with cells of the monocytic lineage by regulating their ability to produce growth factors that ultimately affect both T and B lymphocytic subsets. Therefore, in this study, we examined whether this agent affects the antigenic response of immune cells and determined the relative numbers of immune cells in the murine spleen after in vitro and in vivo treatment. The results showed that L-Cn reduces the relative numbers of CD8+, CD4+ and Ly5+ cells. This observation was consistent in all systems studied including (a) in vitro inoculation of antigen (DNP-HSA) and L-Cn, (b) in vitro priming of spleen cells treated with L-Cn in vivo, and (c) in vivo immunization and L-Cn administration. In all cases, the reduction of T lymphocytes correlated with the decreased production of interleukin-2. L-Cn, however, did not affect the production of specific antibody, which indicates that the observed reduction of Ly5-positive cells is due to cell differentiation of B cells to plasma cells.

Animals↗
PubMedDate not supplied

[Spin label study of microviscosity and structural transitions in cell membrane lipids and proteins. I. Heat-induced structural changes in cell nuclei of mouse organs in normal conditions].

With the help of weakly bound spin probes the effect of temperature on structural transitions of protein and lipid components in the nuclei membranes of different organs of intact mice has been studied. Microviscosity of lipids in the membrane is found to differ sharply from proteins. Found by both probes breaks on Arrhenius curve of the correlation time dependence on reverse temperature within the temperature range of 25degreesC--27degreesC and 40degreesC-43degreesC seem to be connected with structural reconstructions of the whole membrane. The results obtained according to the behaviour of probes are identical for the nuclei of different organs.

Animals↗
PubMed2006

Donor corneas for transplantation: a scanning electron microscopic study of the epithelium.

PURPOSE: Donor corneas are processed in eye banks and used for transplantation as a standard routine. The maximum time limit post-mortem for harvesting donor tissue varies greatly between eye banks. This study aimed to examine the corneal epithelium for structural changes post-mortem. METHODS: A total of 51 corneas harvested between 14 and 163 hours post-mortem were examined using scanning electron and light microscopy. RESULTS: Cell loss occurred through desquamation of flat superficial cells during the first days. In corneas with a post-mortem time of more than 2-3 days, large superficial cell sheets and deeper cells detached, starting centrally. Deep peripheral cells remained. The loss of the superficial cells revealed the 3-dimensional structure of the epithelium and the membrane characteristics of deeper cells. CONCLUSION: The longer the time post-mortem, the greater the epithelial cell loss. However, a rim of peripheral cells remained, even after 7 days. The superficial cell layer showed signs of strong lateral attachment and broke up in a sheet-like fashion. The intercellular adhesion between deeper cells and adhesion between the basal cells and the basement membrane appeared to be weak post-mortem. The cell membrane structures of the remaining cells were surprisingly well retained. The clinical implication of the study is discussed.

Adult↗
PubMed1982

Studies on HeLa cells surface glycopeptides alterations in membrane structure during the cell cycle.

Limited exposure of intact HeLa cells to proteolytic enzymes results in the release of fragments of membrane glycoproteins in the form of glycopeptides. Enriched and partially purified fractions from these glycopeptides are potent inhibitors of protein synthesis in cell-free systems and in intact cells. A comparison of the in vivo and in vitro response revealed that a substantial proportion of protein synthesis in intact cells is resistant to inhibition. When HeLa cell surface glycopeptides (HSP) induced inhibition of protein synthesis was studied in synchronized cell cultures it was found that G1 phase cells are most sensitive to HSP. A cell cycle dependent alteration in the availability of HSP to protease release was also observed. Cells in S phase yield the greatest amount of HSP upon limited proteolysis. The data suggest that alterations in membrane structure at the termination of S phase result in a conversion of membrane glycoproteins from a protease sensitive to a protease resistant state.

Cell Membrane↗
PubMed1972

The fluid mosaic model of the structure of cell membranes.

A fluid mosaic model is presented for the gross organization and structure of the proteins and lipids of biological membranes. The model is consistent with the restrictions imposed by thermodynamics. In this model, the proteins that are integral to the membrane are a heterogeneous set of globular molecules, each arranged in an amphipathic structure, that is, with the ionic and highly polar groups protruding from the membrane into the aqueous phase, and the nonpolar groups largely buried in the hydrophobic interior of the membrane. These globular molecules are partially embedded in a matrix of phospholipid. The bulk of the phospholipid is organized as a discontinuous, fluid bilayer, although a small fraction of the lipid may interact specifically with the membrane proteins. The fluid mosaic structure is therefore formally analogous to a two-dimensional oriented solution of integral proteins (or lipoproteins) in the viscous phospholipid bilayer solvent. Recent experiments with a wide variety of techniqes and several different membrane systems are described, all of which abet consistent with, and add much detail to, the fluid mosaic model. It therefore seems appropriate to suggest possible mechanisms for various membrane functions and membrane-mediated phenomena in the light of the model. As examples, experimentally testable mechanisms are suggested for cell surface changes in malignant transformation, and for cooperative effects exhibited in the interactions of membranes with some specific ligands. Note added in proof: Since this article was written, we have obtained electron microscopic evidence (69) that the concanavalin A binding sites on the membranes of SV40 virus-transformed mouse fibroblasts (3T3 cells) are more clustered than the sites on the membranes of normal cells, as predicted by the hypothesis represented in Fig. 7B. T-here has also appeared a study by Taylor et al. (70) showing the remarkable effects produced on lymphocytes by the addition of antibodies directed to their surface immunoglobulin molecules. The antibodies induce a redistribution and pinocytosis of these surface immunoglobulins, so that within about 30 minutes at 37 degrees C the surface immunoglobulins are completely swept out of the membrane. These effects do not occur, however, if the bivalent antibodies are replaced by their univalent Fab fragments or if the antibody experiments are carried out at 0 degrees C instead of 37 degrees C. These and related results strongly indicate that the bivalent antibodies produce an aggregation of the surface immunoglobulin molecules in the plane of the membrane, which can occur only if the immunoglobulin molecules are free to diffuse in the membrane. This aggregation then appears to trigger off the pinocytosis of the membrane components by some unknown mechanism. Such membrane transformations may be of crucial importance in the induction of an antibody response to an antigen, as well as iv other processes of cell differentiation.

Agglutination↗
PubMed1976

Alterations in lipid acyl group composition and membrane structure in cells transformed by Rous sarcoma virus.

The acyl group composition of the phospholipids from normal chick embryo fibroblasts and from cells transformed by Rous sarcoma virus was determined by gas-liquid chromatography. Rous-transformed cells had less arachidonate (20:4) and more oleate (18:1) in membrane lipids than normal, growing cells. Normal density-inhibited cells had the lowest ratio of 18:1/20:4. Associated with the decreased content of 20:4 in the transformed cells was a decreased motional freedom of an incorporated spin-labeled fatty acid analogue. Arrhenius plots for uptake of 2-deoxyglucose revealed an increased apparent activation energy in the transformed cells, suggesting that the hexose transport carriers were sensitive to the changes in membrane composition and structure in fully transformed cells. However, the development of the changes in fatty acid composition occurred relatively slowly in the course of transformation, indicating that the observed compositional alterations are not likely to be a primary cause of the early changes in membrane function associated with malignant transformation.

Animals↗
PubMed2000

The mode of antimicrobial action of the essential oil of Melaleuca alternifolia (tea tree oil).

The essential oil of Melaleuca alternifolia (tea tree) exhibits broad-spectrum antimicrobial activity. Its mode of action against the Gram-negative bacterium Escherichia coli AG100, the Gram-positive bacterium Staphylococcus aureus NCTC 8325, and the yeast Candida albicans has been investigated using a range of methods. We report that exposing these organisms to minimum inhibitory and minimum bactericidal/fungicidal concentrations of tea tree oil inhibited respiration and increased the permeability of bacterial cytoplasmic and yeast plasma membranes as indicated by uptake of propidium iodide. In the case of E. coli and Staph. aureus, tea tree oil also caused potassium ion leakage. Differences in the susceptibility of the test organisms to tea tree oil were also observed and these are interpreted in terms of variations in the rate of monoterpene penetration through cell wall and cell membrane structures. The ability of tea tree oil to disrupt the permeability barrier of cell membrane structures and the accompanying loss of chemiosmotic control is the most likely source of its lethal action at minimum inhibitory levels.

Anti-Bacterial Agents↗
PubMed1997

A markedly disrupted skeletal network with abnormally distributed intramembrane particles in complete protein 4.1-deficient red blood cells (allele 4.1 Madrid): implications regarding a critical role of protein 4.1 in maintenance of the integrity of the red blood cell membrane.

Electron microscopic (EM) studies were performed to clarify the interactions of membrane proteins in the red blood cell membrane structure in situ of a homozygous patient with total deficiency of protein 4.1 who carried a point mutation of the downstream translation initiation codon (AUG --> AGG) of the protein 4.1 gene [the 4.1 (-) Madrid; Dalla Venezia et al, J Clin Invest 90:1713, 1992]. Immunologically, as expected, protein 4.1 was completely missing in the red blood cell membrane structure in situ. A markedly disrupted skeletal network was observed by EM using the quick-freeze deep-etching method and the surface replica method, although the number of spectrin molecules was only minimally reduced (395 +/- 63/microm2; normal, 504 +/- 36/microm2). The number of basic units in the skeletal network was strikingly reduced (131 +/- 21/microm2; normal, 548 +/- 39/microm2), with decreased small-sized units (17 +/- 4/microm2; normal, 384 +/- 52/microm2) and increased large-sized units (64% +/- 14%; normal, 5% +/- 1%). Concomitantly, immuno-EM disclosed striking clustering of spectrin molecules with aggregated ankyrin molecules in the red blood cell membrane structure in situ. Although no quantitative abnormalities in the number and size distribution of the intramembrane particles were observed, there was a disappearance of regular distribution, with many clusters of various sizes, probably reflecting the distorted skeletal network. Therefore, protein 4.1 suggests by EM to play a crucial role in maintenance of the normal integrity of the membrane structure in situ not only of the skeletal network but also of the integral proteins.

Anemia, Hemolytic↗
PubMed1992

The cryoprotective effect of antifreeze glycopeptides from antarctic fishes.

Apparently vitrified cells and tissues often fail to survive, probably from damage from growth of microscopically invisible ice crystals. Special biological antifreezes from some polar fishes have been shown to adsorb to specific faces of ice crystals and inhibit crystal growth. Vitrification in the presence of antifreezes therefore may help enhance postvitrification viability of cells and tissues. We report here that the addition of fish antifreeze glycopeptides (AFGPs) to vitrifying solutions increases post-thaw viability in cultured immature pig oocytes and two-cell stage embryos of mice and pigs after rapid cooling to cryogenic temperatures. The criterion for viability is maturation to metaphase for the oocytes and the ability to develop into the four-cell stage for the pig embryo and the blastocyst stage for the mouse embryo. Without AFGPs, or with addition of antifreeze peptides (AFPs), the particular vitrifying solution and cooling/warming/culturing regime used in this study produced zero viability. In the presence of the AFGPs (40 mg/ml), survival of pig oocytes and embryos was increased to about 25%, and that of mouse embryos to 82%. Dose-response studies for the mouse embryos showed that the protective effect of AFGPs shows saturation kinetics and levels off at 20 mg/ml. The AFGPs appeared to preserve cell membrane structural integrity; however, an intact cell membrane did not always lead to viability. The absence of protective effect by AFPs suggests that protection by the AFGPs is unrelated to their common antifreeze property, i.e., inhibition of ice crystal growth, but probably results from interaction with and stabilization of the cell membranes unique to the AFGPs.

Animals↗
PubMed2004

Ortho-substituted PCBs kill cells by altering membrane structure.

Our previous studies have demonstrated that ortho-substituted PCBs cause a rapid cell death in both thymocytes and cerebellar granule cell neurons, whereas coplanar congeners are without effect at comparable concentrations and exposure times. We have demonstrated that multiple membrane components are altered by these exposures, including the plasma membrane, mitochondria, and endoplasmic reticulum. The present experiments were designed to test the hypothesis that because of their stereochemistry, ortho-substituted congeners cause a greater disruption of membrane integrity than do coplanar congeners, and that this membrane disruption results in altered cellular function and to cell death. To test this hypothesis we have measured fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) in thymocytes, cerebellar granule cells, and lipid bilayer vesicles upon exposure to an ortho-substituted PCB congener (PCB 52) and a coplanar congener (PCB 77), and compared results obtained in these studies to those from flow cytometric studies of plasma membrane permeability to large molecules and elevations of intracellular calcium in living cells. The fluorescence polarization of the DPH probe, which inserts into the lipid bilayer, reflects changes in membrane fluidity. In all three preparations we found that whereas fluorescence polarization was unchanged upon exposure to PCB 77, it was reduced significantly by PCB 52, reflecting an increase in membrane fluidity. These observations are consistent with the hypothesis that ortho-substituted PCBs disrupt membrane structure, which alters the function of membrane proteins. In the two cell types we have studied, the disruption is sufficient to cause death of the cell within a brief time.

Animals↗
PubMed1981

The lipids of red cell membranes. Compositional, structural and functional aspects.

The structural matrix of the erythrocyte membrane is provided by a lipid bilayer containing more than one hundred different molecular species of lipid. The phospho- and glycolipids are distributed over the two halves of the bilayer in a highly asymmetric fashion; the outer monolayer consisting of all the glycolipids and the greater part of the two choline-containing phospholipids, whereas the amino-containing phospholipids dominate the inner monolayer. Functional implications of this arrangement are still poorly understood, but some of them may be found in blood coagulation and lipid-requiring membrane-bound enzymes. The bilayer exhibits a high degree of stability as is illustrated by 31P-NMR studies of membranes treated with phospholipases. However, selective modification of the molecular species of lecithin in the outer monolayer may lead to such destabilizations that the structural integrity of the membrane is lost and the cells haemolyse.

Adenosine Triphosphatases↗
PubMed1989

Imaging of cell membraneous and cytoskeletal structures with a scanning tunneling microscope.

The first observation of unstained cell membraneous structures by a scanning tunneling microscope is reported. An adhesive preparation method was used for imaging human medulloblastoma cells from the cell line TE 671 and oocytes from the clawed toad Xenopus laevis. The images show filaments, stacks of molecules and hilly structures. The possible identify of the filamentous structures is discussed, although the observed structures cannot yet be fully characterized. The work suggests possible future experiments on various biological structures in their natural environment.

Animals↗
PubMed2005

Contribution to comprehension of image formation in confocal microscopy of cornea with Rostock cornea module.

AIM: To investigate the influence of refractive index of aqueous humour on imaging of corneal endothelium in confocal microscopy. To clarify the phenomenon of dark endothelial and bright epithelial cell membranes in confocal images of corneas. METHODS: Use of a novel digital confocal laser scanning microscope, a combination of the Heidelberg retina tomograph (HRT II) and the Rostock cornea module. Exchange of aqueous humour solution from domestic pigs against glycerol/water solutions (refractive indices eta = 1.337-1.47). Transelectron microscopy of endothelial and epithelial cell morphology. RESULTS: Under the terms of variable refractive indices no differences were observed for general imaging of endothelium. Bright cells were bordered by dark cell membranes in all experiments. Electron microscopy of endothelium and epithelium revealed differences in intracellular and cell membrane structure of both cell types. CONCLUSION: Source of specific confocal optical behaviour of endothelium does not come from interface conditions to aqueous humour, but may result from intracellular variations and ultrastructure of cell membranes.

Animals↗
PubMed1992

Effect of graded hypoxia on brain cell membrane injury in newborn piglets.

Alterations in brain cell membrane structure and function during cerebral hypoxia were investigated by measuring Na+,K(+)-ATPase activity and levels of lipid peroxidation products in brain cell membranes obtained from newborn piglets following exposure to 60 min of hypoxic hypoxia in vivo. Cerebral hypoxia was documented as a decrease in the ratio of phosphocreatine to inorganic phosphate (PCr/Pi) using 31P-NMR spectroscopy. During hypoxia (FiO2 0.07-0.11), PCr/Pi decreased 28-47% compared to the corresponding baseline value without a decrease in cerebral ATP levels. No change in brain cell membrane Na+,K(+)-ATPase activity was observed for changes in PCr/Pi of less than 30%. When PCr/Pi was at least 30% lower than baseline, Na+,K(+)-ATPase activity decreased linearly as a function of the decrease in PCr/Pi (r = 0.95). Levels of lipid peroxidation products (conjugated dienes and fluorescent compounds) increased significantly as PCr/Pi decreased. These data suggest that below a critical threshold value of oxidative metabolism there are progressive changes in brain cell membrane structure and function during cerebral hypoxia, and demonstrate that membrane alterations occur prior to changes in cellular ATP levels.

Animals↗