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Biomedical subjects

G Poste

Publications and source records attributed to G Poste.

At least 145 records · Page 8Linked to original sources
PubMed1976

Measurement of the lateral mobility of cell surface components in single, living cells by fluorescence recovery after photobleaching.

The use of fluorescence recovery after photobleaching (FRAP) techniques to monitor the lateral mobility of plant lectin-receptor complexes on the surface of single, living mammalian cells is described in detail. FRAP measurements indicate that over 75% of the wheat germ agglutinin receptor (WGA-receptor) complexes on the surface of human embryo fibroblasts are mobile. These WGS-receptor complexes diffuse laterally (as opposed to flow) on the cell surface with a diffusion coefficient in the range of 2 X 10(-11) to 2 X 10(-10) cm2/sec. Both the percentage of mobile WGA-receptor complexes and the mean diffusion coefficient of these complexes are higher than that obtained from earlier FRAP measurements of the mobility of concanavalin A-receptor (Con A-receptor) complexes in a variety of cell types. The possible reasons for the differing mobilities of WGA and Con A receptors are discussed.

Cell Line↗
PubMed1976

Lipid vesicles as carriers for introducing materials into cultured cells: influence of vesicle lipid composition on mechanism(s) of vesicle incorporation into cells.

The mechanisms involved in the uptake of uni- and multi-lamellar lipid vesicles by BALB/c mouse 3T3 cells have been investigated. Vesicles are incorporated into cells both by endocytosis and by a nonendocytotic mechanism which we propose involves fusion of vesicles with the plasma membrane. The nonendocytotic pathway predominates in the uptake of negatively charged vesicles composed of phospholipids that are "fluid" (phosphatidylserine/phosphatidylcholine) at 37 degrees. Neutral fluid vesicles (phosphatidylcholine) and negatively charged vesicles prepared from "solid" phospholipids (phosphatidylserine/distearylphosphatidylcholine/dipalmitoylphosphatidylcholine) are instead incorporated largely by endocytosis. Uptake of the latter classes of vesicle is reduced (80-90% inhibition) by inhibitors of cellular energy metabolism and by cytochalasin B.

Azides↗
PubMed1976

Effects of local anesthetics on cell morphology and membrane-associated cytoskeletal organization in BALB/3T3 cells.

Tertiary amine local anesthetics (dibucaine, tetracaine, procaine) reversibly affect the morphology of untransformed BALB/3T3 cells and the organization of membrane-associated cytoskeletal elements. In the presence of these drugs cells contract and become rounded in shape with the appearance of numerous surface "blebs." Electron microscope examination of anesthetic-treated cells revealed significant reductions in plasma membrane-associated microtubules and microfilaments and/or their plasma membrane attachment. The relationship of the findings on local anesthetic-induced changes in cellular cytoskeletal systems is discussed in relation to previous proposals on plasma membrane organization and control of cell surface receptor topography and mobility.

Cell Line↗
PubMed1976

Use of lipid vesicles as carriers to introduce actinomycin D into resistant tumor cells.

Unilamellar lipid vesicles have been used as a carrier vehicle to enhance the uptake of actinomycin D into an actinomycin D-resistant Chinese hamster tumor cell line (DC-3F/ADX). The DC-3F/ADX cell line is resistant to actinomycin D as a result of its decreased capacity to transport actinomycin D across the plasma membrane and is able to grow in the presence of concentrations of actinomycin D that are cytotoxic for the sensitive parent cell line (DC-3F). Incubation of resistant DC-3F/ADX cells with actinomycin D-containing vesicles produced a 5-fold increase in intracellular drug concentration over that achieved by exposure to identical concentrations of the drug added to the culture medium. Vesicle-mediated uptake of actinomycin D into resistant cells produced inhibition of cellular RNA synthesis and cell growth at actinomycin D concentrations that had no inhibitory effect when added as free drug in the culture medium. Dose-response measurements established that direct introduction of actinomycin D into resistant cells by means of lipid vesicles resulted in a 200-fold reduction in the concentration of actinomycin D required to inhibit cellular RNA synthesis and a 120-fold reduction in the dose of actinomycin D required to produce a 50% inhibition of cell growth. These results lend strong support to the hypothesis that cellular resistant to actinomycin D is due to a lower capacity to take up actinomycin D as a result of a reduction in the permeability of the cellular plasma membrane to this drug. The potential value of lipid vesicles for introducing other classes of drugs into cultured cells and their possible use in chemotherapy are also discussed.

Animals↗
PubMed1975

Some electrical properties of the peripheries of murine 3T3 cells with respect to viral transformation and reversion.

Mouse 3T3, Simian virus 40 transformed 3T3 cells (SV3T3) and two SV3T3 lines showing reversion of their transformed phenotype (Rev 3 and Rev 5) have been studied with respect to electrophoretic mobilities and colloidal iron hydroxide (CIH) binding density visible by electron microscopy, before and after incubation with neuraminidase or ribonuclease. The results show that, in general, the marked changes in both sets of surface parameters associated with transformation are largely reversed in the Rev 5 revertant, and only partially reversed in the Rev 3 line. It was also observed that, in common with Ehrlich ascites tumor (EAT) cells examined previously, the densities of CIH-particles bound over the microvilli of all the cell types was 1.5 to 2.7 times higher than those bound to the spaces between them. In contrast to the EAT cells, the higher density of CIH particles bound over the microvilli was not due to neuraminidase-sensitive binding sites.

Animals↗
PubMed1975

Effects of local anesthetics on membrane properties. I. Changes in the fluidity of phospholipid bilayers.

The effect of the local anesthetic dibucaine on the solid to liquid-crystalline phase transition in phospholipid vesicles was studied by calorimetry and fluorescence polarization. The partition coefficient (greater than 3000) of dibucaine in the membranes of vesicles prepared from acidic phospholipids was more than 20 times higher than in neutral phospholipid membranes under the same conditions. Calorimetric measurements on vesicles prepared form acidic phospholipids (bovine brain phosphatidylserine; dipalmitoylphosphatidylglycerol) showed that dibucaine (1 with 10(-4) M) produced a significant reduction in the gel-liquid crystalline transition temperature (Tc). This fluidizing effect of dibucaine on acidic phospholipid membranes was even more marked in the presence of Ca2+. In contrast, dibucaine at the same concentration did not alter the Tc of neutral phospholipids (dipalmitoylphosphatidylcholine). Significant increase in the fluidity of neutral phospholipid membranes occurred only at higher dibucaine concentrations (2 with 10(-3) M). Measurements of the fluorescence polarization and lifetime of the probe, 1,6-diphenylhexatriene, in acidic phospholipid vesicles revealed that dibucaine (1 with 10(-4) M) caused an increase in the probe rotation rate indicating an increase in the fluidity of the phospholipid membranes. A good correlation was obtained between fluorescence polarization data on dibucaine-induced changes in membrane fluidity and calorimetric measurements on vesicles of the same type.

Anesthetics, Local↗
PubMed1975

Effects of local anesthetics on membrane properties. II. Enhancement of the susceptibility of mammalian cells to agglutination by plant lectins.

Treatment of untransformed mouse and hamster cells with the tertiary amine local anesthetics dibucaine, tetracaine and procaine increases their susceptibility to agglutination by low doses of the plant lectin concanavalin A. Agglutination of anesthetic-treated untransformed cells by low doses of concanavalin A is accompanied by redistribution of concanavalin A receptors on the cell surface to form patches, similar to that occurring in spontaneous agglutination of virus-transformed cells by concanavalin A. Immunofluorescence and freeze-fracture electronmicroscopic observations indicate that local anesthetics per se do not induce this redistribution of concanavalin A receptors but modify the plasma membrane so that receptor redistribution is facilitated on binding of concanavalin A to the cell surface. Fluorescence polarization measurements on the rotational freedom of the membrane-associated probe, diphenylhexatriene, indicate that local anesthetics produce a small increase in the fluidity of membrane lipids. Spontaneous agglutination of transformed cells by low doses of concanavalin A is inhibited by colchicine and vinblastine but these alkaloids have no effect on concanavalin A agglutination of anesthetic-treated cells. Evidence is presented which suggests that local anesthetics may impair membrane peripheral proteins sensitive to colchicine (microtubules) and cytochalasin-B (microfilaments). Combined treatment of untransformed 3T3 cells with colchicine and cytochalasin B mimics the effect of local anesthetics in enhancing susceptibility to agglutination by low doses of concanavalin A. A hypothesis is presented on the respective roles of colchicine-sensitive and cytochalasin B-sensitive peripheral membrane proteins in controlling the topographical distribution of lectin receptors on the cell surface.

Agglutination↗
PubMed1975

Cochleate lipid cylinders: formation by fusion of unilamellar lipid vesicles.

Freeze-fracture electron microscopy was used to study the morphological changes occurring following the addition of Ca-2+ to sonicated preparations of phosphatidylserine in aqueous NaCl buffer. Before the addition of Ca-2+, preparations contained only small (200-500 A diameter) spheroidal vesicles. After the addition of Ca-2+ (10 mM) and incubation for 1 h at 37 degrees C preparations contained only large (2000-10 000 A) apparently multilamellar structures many of which were cylindrical in shape. The lamellae in these cylinders appear to be folded in a spiral configuration. Addition of EDTA to these preparations produced large, closed, spherical, unilamellar vesicles. We suggest the name cochleate lipid cylinders for the spiral structures and propose that they are formed by fusion of unilamellar vesicles into large sheets which fold spirally to form cylinders.

Calcium↗
PubMed1975

Interaction of concanavalin A with the surface of virus-infected cells.

Infection of untransformed cells with a wide-range of non-oncogenic enveloped viruses causes a significant increase in their susceptibility to agglutination by concanavalin A (Con A). The increased Con A agglutinability of these cells is not caused by an increase in the number of Con A sites on the cell surface but involves alteration in the surface properties of infected cells to allow redistribution of Con A receptors to form "patches" following binding of Con A to the cell surface. Similarities between Con A-mediated agglutination of normal cells infected with non-oncogenic viruses and the agglutination response to cells transformed by oncogenic viruses will be reviewed. Finally, the use of Con A as an experimental tool to modify the replication and cytopathogenicity of non-oncogenic viruses grown in mammalian cells will be presented.

Agglutination↗
PubMed1975

Local anesthetics affect transmembrane cytoskeletal control of mobility and distribution of cell surface receptors.

Tertiary amine local anesthetics facilitated concanavalin A-induced redistribution of lectin receptors on murine BALB/3T3 cells and enhanced the susceptibility of these cells to agglutination by concanavalin A. In contrast, these drugs at similar concentrations inhibited ligand-induced capping of immunoglobulin receptors on mouse lymphocytes. We propose that these differing effects of local anesthetics on membrane receptor mobility in fibroblasts and lymphocytes result from the action of anesthetics on membrane-associated microtubules and microfilaments involved in the transmembrane control of receptor mobility. We present electron microscopic evidence of structural alterations in microtubule and microfilament organization in anesthetic-treated cells, together with data on changes in the responsiveness of anesthetic-treated cells to drugs that act on microtubules and/or microfilaments. This evidence supports the proposal that anesthetics affect the organization of cytoskeletal components or their plasma membrane attachment points. The effects of local anesthetics on ligand-induced redistribution of membrane receptors in both 3T3 cells and lymphocytes can be duplicated by treating cells with colchicine (or Vinca alkaloids) together with cytochalasin B. We propose that the participation of membrane-associated microtubules and microfilaments in the transmembrane control of receptor mobility is such that microtubules and microfilaments play opposing roles in regulating the mobility and topography of cell surface receptors.

Anesthetics, Local↗
PubMed1975

Growth of mammalian cells on substrates coated with cellular microexudates. I. Effect on cell growth at low population densities.

Mammalian and avian cells cultured on glass or plastic substrates produce microexudates of cellular macromolecules which remain bound to the substrate when the cells are detached. The gross macromolecular composition of microexudates from a range of diploid, heteroploid, and virus-transformed cells was determined with cells labeled with radioisotopes. Significant differences in the amounts of cellular glycoproteins, proteins, and RNA present in microexudates were found between different cell types and between cells of the same type at different stages of growth. Inoculation of cells onto substrates "coated" with microexudates altered their growth behavior. Microexudates from exponentially growing subconfluent homotypic and heterotypic cell populations enhanced the growth of mouse and chick embryo cells seeded at very low densities, but similar microexudates had no effect on the proliferation of cells seeded at higher densities. The enhanced growth of low-density cell populations seeded on microexudates was compared with the growth enhancement produced by feeder cell layers and conditioned medium.

Animals↗