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Biomedical subjects

L B Margolis

Publications and source records attributed to L B Margolis.

At least 55 records · Page 3Linked to original sources
PubMed1988

Induction of intercellular communications in epithelial cell cultures.

A popular criterion of cell-cell communication in tissue cultures is dye coupling: the ability of the injected fluorescent dye of low molecular weight to be transferred from one cell to another. We report about a new factor which induces cell-to-cell dye coupling in previously uncoupled epithelial sheets. Paradoxically it is the standard fluorescent microscopy itself (that is, blue light of 320- to 480-nm wavelength) which induces rapid morphological alterations of cell culture followed by the transfer of fluorescent dye from one cell to another. Thus monitoring cell-cell dye coupling by fluorescent microscopy may itself induce the dye coupling in previously uncoupled epithelial cells.

Animals↗
PubMed1988

Formation of cell outgrowths by external force: a model study.

Cell outgrowth formation by a force applied to the external membrane was investigated. This extrinsic force, which is generated in a special chamber by an alternating current (AC) electric field (EF) of high frequency, pulls the membrane outwards. The force arises due to the redistribution of ions beneath the cell surface and is applied to the thin (10-20 A) undermembrane layer. This force is sufficient to generate cell-specific membrane protrusions of various types. The morphology of these protrusions in mouse embryo and human fibroblasts, and in mouse L cells, resembles that of the outgrowths that these cells form under normal physiological conditions. Ehrlich ascites tumour cells (which normally grow in suspension) in an AC EF form only thin short processes. Erythrocytes when subjected to EF treatment are not capable of producing processes at all. An aligned system of microfilaments was found in the outgrowths produced by mouse embryo fibroblasts. However, cytochalasin B, sodium azide + 2-deoxy-D-glucose, carbonyl-m-chlorphenylhydrazon + 2-deoxy-D-glucose, colcemid and incubation at 4 degrees C were not able to prevent the generation of processes in an EF. It is proposed that the morphology of cell protrusions is determined by the structure of the domains in the plasma membrane, rather than by active cytoskeletal reorganization. The experimental system that we developed provides an opportunity for studying the mechanical linkages of cytoskeletal elements with the plasma membrane.

Animals↗
PubMed1987

Acidification of the interior of Ehrlich ascites tumor cells by nigericin inhibits DNA synthesis.

In Ehrlich ascites carcinoma cells, acidification of the cytoplasm down to pH 6.2-6.3 arrests DNA synthesis. Such acidification can be obtained by decreasing the pH outside the cell or, alternatively, by addition of a micromolar concentration of the K+/H+ antiporter nigericin. Thus, nigericin may be regarded as a new type of cytostatic, the effect of which is mediated by alteration of the intracellular pH.

Animals↗
PubMed1986

[Interaction of epithelial cells with the edges of fluid and solid lipid films].

Capping of Concanavalin A (Con A) on the surface of epithelial cells near the cell-cell contacts has been compared with that in the regions of cell contacts with the edges of lipid films. If the lipids are in "fluid" state, Con A is capped likely as on the free edges of epithelial sheets, while contacts with the edge of solid lipid film inhibit capping of Con A as do cell-cell contacts. The same is true for capping of liposomes adsorbed on the surface of epithelial cells. We suppose that solid rather than fluid domains in plasma membranes may play a significant role in establishing cell-cell contacts.

Animals↗
PubMed1985

[Competition of solid and fluid liposomes for binding and metabolism with lipids from the cell surface].

The competitive behavior of solid vs. fluid liposomes in liposome-cell adsorption and cell-to-liposome lipid transfer processes was investigated with L cells and FBT epithelial sheets. Binding and transfer experiments have demonstrated that: solid liposomes adhere to the cell surface as integral vesicles retaining the entrapped substance; fluid liposomes are partly disintegrated at the cell surface with concomitant entry of entrapped substances into the cytoplasm, while their lipids remain on the cell surface; fluid liposomes that escape lysis dissociate from the cell taking away cell lipid molecules. No lipid transfer occurs between the plasma membrane and solid liposomes. Cell-bound solid liposomes interfere with the transfer of cell lipids to fluid liposomes, while these in turn inhibit the binding of solid liposomes to the cell surface.

Animals↗
PubMed1984

Lipid-cell interactions. Liposome adsorption and cell-to-liposome lipid transfer are mediated by the same cell-surface sites.

The competitive behavior of solid vs. fluid liposomes in liposome-to-cell adsorption and cell-to-liposome lipid transfer processes was investigated with L cells and FBT epithelial sheets. Binding, transfer and 31P-NMR experiments have demonstrated that: (i) solid liposomes adhere to the cell surface as integral vesicles retaining the entrapped substances; (ii) fluid liposomes are partly disintegrated at the cell surface with concomitant entry of entrapped substances into the cytoplasm, while their lipids remain on the cell surface; (iii) fluid liposomes that escape lysis dissociate from the cell, taking away cell lipid molecules. The latter process underlies the mechanism of cell-to-fluid liposome lipid transfer. In contrast, no lipid transfer occurs between the plasma membrane and solid liposomes. Cell-bound solid liposomes interfere with the transfer of cell lipids to fluid liposomes, while these in turn inhibit the binding of solid liposomes to the cell surface. Moreover, cell-induced aggregation of both fluid and solid freshly added liposomes is also inhibited by preincubation of the cells with either solid or fluid liposomes. Thus, different types of interaction of both fluid and solid liposomes with the cell are mediated by the same (or closely related) sites on the cell surface.

Adsorption↗
PubMed1983

Magnetoliposomes: another principle of cell sorting.

Liposomes bearing anti-fibronectin antibodies and associated with ferromagnetic particles bound firmly to the surface of mouse embryo fibroblasts. Upon binding magnetoliposomes, the cells could be sorted in a magnetic field.

Animals↗
PubMed1983

Liposomes inhibit intercellular attachment.

Phosphatidylcholine liposomes bound to the surface of L cells inhibit cell attachment to L-cell monolayers or to lipid films. Aggregation of L cells or of mouse embryo fibroblasts is also diminished upon treatment with liposomes. However, they neither inhibit cell attachment to glass or cellulose acetate substrata, nor diminish conA-mediated cell aggregation. It is supposed that liposome-binding sites on the cell surface described earlier are involved in cell-cell attachment.

Animals↗
PubMed1983

[Distribution of solid liposomes on the surface of an epithelial cell layer].

A study was made of the adhesion of liposomes, composed of dipalmitoyl- or di-stearoylphosphatidycholine, on the surface of epithelial cells in culture. Sodium fluorescein was entrapped in liposomes for their visualization by fluorescence microscopy. It is found that sonicated unilamellar liposomes adhere predominantly along the sheet margins. Multilamellar liposomes and lipid-coated carmine particles adhere over the whole cellular surface. However, their adhesion along sheet margins was stronger, as evidenced by a brief trypsin treatment. A prolonged trypsin treatment removed all types of liposomes from the cell surface. After the cells were partly detached from each other, small liposomes readily adhered to the newly accessible cell margins. The existence of special lipid membrane-binding proteins on the cell surface is suggested.

Adsorption↗
PubMed1983

The distribution of solid liposomes of different size on the surface of epithelial cells.

Interaction of large multilamellar and small sonicated liposomes with epithelial sheets in culture has been studied. Liposomes were comprised of dipalmitoyl- or distearoylphosphatidylcholine and were solid at 37 degrees. Sodium fluorescein was entrapped in liposomes and their localization on the cell surface was studied by fluorescence microscopy. The distribution of liposomes depends on their size. Large liposomes adhere uniformly all over the surface of the sheet, which proved to be nonadhesive either for other cells or for inert particles. Small liposomes adhere mostly along the margins of the sheet. When the cells are partly detached from each other by mild EDTA (ethylene diamine tetraacetic acid) treatment, the newly accessible cell margins become capable of binding small liposomes. The binding of both types of liposomes is trypsin-sensitive; however large liposomes, bound along the edges of the cellular sheet, are removed slower than those adhering to the inner parts of the sheet. Competition experiments show that large and small liposomes bind to the same sites on the surface of the sheet. Liposome-acceptor proteins are suggested to exist on the surface of epithelial cells. We suppose that these proteins are concentrated along the cell margins and are involved in cell-cell contacts.

Animals↗
PubMed1982

Lipid-cell interactions. A novel mechanism of transfer of liposome-entrapped substances into cells.

A new approach has been developed for studying the transfer of liposome-entrapped substances into cells. The cells are incubated with liposomes containing two markers that in the free (non-entrapped) state enter the cells at different rates. Comparison of the ratio of cell-associated markers applied either in free or in liposome-entrapped form permits the evaluation of different pathways of cellular uptake of the intraliposomal substances. When epithelial cell sheets were incubated with egg phosphatidylcholine liposomes containing two different sugars they became cell-associated at a ratio different from their initial ratio inside the liposomes. Since the cell-associated ratio was shifted towards the value observed when the cells were incubated with a mixture of the two sugars in the free state, it is suggested that the liposomes become permeable during incubation and that the liberated substances enter the cells in the free form. On the other hand, cell-liposome interaction was demonstrated by NMR measurement and gel-filtration experiments to result in transformation of small unilamellar liposomes into larger multilayered aggregates. This transformation depends on the contact of the liposomes with the cell sheet. It is supposed that interliposomal aggregation is the underlying mechanism of cell-induced leakage of liposomes.

Biological Transport↗
PubMed1980

Platelet adhesion to fluid and solid phospholipid membranes.

We have studied platelet adhesion to phospholipid model membranes in vitro. Our results showed that films made of egg lecithin, dioleoyllecithin or phosphatidylethanolamine from two different sources (egg yolk and E. coli) are unadhesive for platelets. Platelets adhered to films made of distearoyllecithin, dipalmitoyllecithin and N--stearoylsphingomyelin. According to electron spin resonance measurements, the former lipids were present during incubation with platelet-rich plasma above the phase transition temperature, whereas the latter were present below this temperature. Cross-linking of phosphatidylethanolamine films with glutaraldehyde or egg lecithin, as well as dioleoyllecithin with OsO4, abolishes the phase transition of the lipids in these films, transforming them to the solid state. After such treatment the films become adhesive for platelets. Thus fluid liquid crystalline phospholipid membranes are unadhesive for platelets; solid crystalline (gel) films are adhesive for these cells. We suggest that the fluidity of the plasma membrane has an essential role in making the endothelium unadhesive for platelets in vivo.

Animals↗