PubMed Health⌕ Search

Biomedical subjects

I Ophir

Publications and source records attributed to I Ophir.

17 recordsLinked to original sources
PubMed1999

Induced differentiation in HT29, a human colon adenocarcinoma cell line.

The human colon adenocarcinoma cell line HT29 displays an undifferentiated phenotype under standard growth conditions. When these cells were cultured for 21 days and then treated with forskolin, most of the cells formed brush borders on their apical surfaces. Brush border formation was inhibited by cytochalasin D but not by colchicine. Colchicine, nocodazole and taxol were found to induce differentiation and apoptosis in HT29 cells. Differentiation was characterized by flattening of the cells, formation of brush borders on apical surfaces and tight junctions between adjacent cells. Apoptosis was characterized by detachment of round cells from the cell layer, condensation of nuclear DNA and annexin V binding to cell surfaces. Treatment with colchicine or forskolin induced the association of E-cadherin to the cytoskeleton fraction of subconfluent HT29 cells. This effect was less prominent in post confluent cells. Our data indicate that microtubule-interfering agents may serve as an important tool in the study of differentiation and apoptosis in intestinal carcinoma.

Antineoplastic Agents↗
PubMed1995

Apical polarity in human colon carcinoma cell lines.

The non-polar human adenocarcinoma cells (HT29) when grown as monolayers or aggregates, have no tight junctions and no brush border. When these cells are treated with forskolin (15-100 microM) or cholera toxin (1 nM) intercellular lumina appear between the cells and about 30% of the cells facing the medium or the lumina are fully covered with a brush border. Aggregates embedded in collagen type I and treated with forskolin form a brush border only on cells facing the intercellular lumina. Monolayers of the polar human colon adenocarcinoma cell line Caco-2 express spontaneously tight junctions and a brush border in all the cells. When grown in aggregates the inner cells lose their polarity and only the cells facing the medium are polar. This polarity was not found when the aggregates were embedded in collagen gels. Aggregates embedded in collagen and treated with forskolin form bubble-like structures with a single layer of polar cells facing a central lumen. The data indicate that cell polarity is probably controlled by both internal factors such as cAMP and external factors such as cell-cell and cell-substratum molecules.

Cell Communication↗
PubMed1990

Effect of temperature on the assembly of tight junctions and on the mobility of lipids in membranes of HT29 cells.

In the human colon adenocarcinoma cell line HT29, tight junctions can be induced by treatment with appropriate proteases or salt solutions. The temperature dependence of induced tight junction formation is characterized by a marked sigmoidal behavior. The different methods of induction used in this study were characterized by threshold temperatures ranging from 15 to 32 degrees C. Fluorescence photobleaching recovery measurements of the lateral diffusion of a fluorescent phospholipid probe in the cellular plasma membrane gave no evidence for a phase transition or for alteration in the organization of membrane lipids in lateral domains in the temperature range between 0 and 37 degrees C. Moreover, dynamic parameters of the probe in the plasma membrane did not change substantially on mild treatment with trypsin. Thus, the temperature dependence of tight junction formation is not dictated by the bulk properties of the cytoplasmic membrane lipids. The observed temperature dependence suggests that the assembly of tight junctions is a cooperative process, which may involve conformational rearrangement in a protein precursor subsequent to its proteolytic activation.

Freeze Fracturing↗
PubMed1989

Effect of protein synthesis inhibitors on formation and degradation of tight junctions in HT 29 adenocarcinoma cells.

The human colon adenocarcinoma cell line HT 29 grows in DMEM virtually without tight junctions (TJ). Fascia occludens type TJ can be induced in these cells by treatment with a variety of proteases or with hypertonic ammonium sulfate solution. The induced formation of TJ is not affected by pretreatment of the cells with cycloheximide or puromycin. The induced TJ are almost completely degraded within 2 h at 37 degrees C both in the absence and presence of the inhibitors studied. With ammonium sulfate as the initial inducing agent, it was possible to induce a second round of TJ formation as early as 2 h after the initial treatment, i.e., immediately after the degradation of the TJ formed in the first round. The same result was obtained in cells treated with cycloheximide. Similar results were also obtained when TJ were initially induced by a very mild trypsin treatment. However, if the initial induction involved a more rigorous proteolytic treatment, the cells needed a recovery period of several h before TJ could be induced again. Under these conditions, recovery from the protease treatment was impaired by the addition of protein synthesis inhibitors at any time prior to complete recovery. It follows that proteolytic treatment of cells not only induces TJ formation but also destroys cell surface proteins which must be available for the formation of TJ strands. It seems possible that these proteins mediate cell adhesion events which may be a prerequisite for, but not a part of the actual TJ formation.

Adenocarcinoma↗
PubMed1988

The effect of sodium hyaluronate on the corneal epithelium. An ultrastructural study.

The effect of sodium hyaluronate (NaHa) 1% and 0.1% was studied on 14-day chick embryo corneal epithelium by scanning electron microscopy. It was found that NaHa 1% or 0.1% had no toxic effects on the chick corneal epithelium and the normal architecture of the cells and the morphology of the microvilli was well preserved. A combination of NaHa 0.1% and benzalkonium chloride (BAK) 0.01% reduced the toxic effect of BAK on the surface corneal epithelium. NaHa 0.1% provided a better protection of the corneal epithelium against dryness than hydroxyethylcellulose (HEC) 0.1% or phosphate buffer saline (PBS).

Animals↗
PubMed1985

Formation of lentoids from retina gliocytes: ultrastructural study.

In primary monolayer cultures of dispersed neural retina cells from 13-day chick embryo, gliocytes (Müller glia cells) multiply and rapidly change into a lentoidal (lens-like) phenotype. They express lens proteins, including MP26 (a lens plasma-membrane antigen) and ultra-structurally appear to resemble lens cells. A significant aspect of this modification is that the glia-derived lentoidal cells no longer display contact-affinity for neurons but become preferentially adhesive to each other; in aggregates, they assemble into compact lentoids. A likely explanation for this change in cell affinities is that the modified gliocytes express little or no R-cognin, a retinal cell-surface antigen implicated in mutual recognition and adhesion of retina cells. Although lentoidal cells express MP26, a gap-junction component in the lens, no gap junctions could be found in the lentoids.

Animals↗
PubMed1984

Cell disorganization and malformation in neural retina caused by antibodies to R-cognin: ultrastructural study.

Retina tissue from 6-day chick embryos was organ-cultured for 3 days in the presence of antibodies to R-cognin, a surface antigen of retina cells. The antibodies which are known to bind to this antigen caused a striking malformation: interruption of the outer limiting membrane and extensive cell disorganization resulting in exteriorization of many cells and forming of chaotic masses on the surface of the tissue. Controls did not show these effects. These results further confirm that R-cognin is involved in the mechanism of histotypic contacts and recognition of retina cells, and that it plays an essential role in cell organization and histogenesis in the retina.

Animals↗
PubMed1983

Localization of retina cognin in embryonic neural retina tissue by immuno-scanning electron microscopy.

The retina cognin (a retina-specific cell-surface glycosylated protein that mediates self-recognition and morphogenetic contact associations of embryonic retina cells) was visualized by immunolabeling and scanning electron microscopy on the surface of cells within retina tissue of 9- and 16-day chick embryos. The photoreceptor processes which are free of contact with cells in the neural retina, were found to be devoid of surface cognin from early on in their development. These results extend previous studies on cognin localization and regeneration on separated retina cells in vitro and conclusively correlate its presence and surface topology with its postulated role.

Animals↗
PubMed1980

ATP-stimulated Ca2+ transport into cholinergic Torpedo synaptic vesicles.

Activation of the Ca2+/Mg2+ ATPase associated with highly purified Torpedo synaptic vesicles results in 45Ca2+ uptake. The accumulated 45Ca2+ is released by hypoosmotic buffer and by the Ca2+ ionophore A23187. Density-gradient centrifugation and permeation chromatography reveal that vesicular acetylcholine and the membrane-bound 45Ca2+ co-migrate, thus implying that 45Ca2+ is transported into cholinergic vesicles. ATP-dependent 45Ca2+ uptake follows saturation kinetics, with KmCa2+ = 50 microM, and Vmax = 3 +/- 0.3 nmol Ca2+/mg protein/min. Treatment of the vesicles with mersalyl, dicyclohexylcarbodiimide, and quercetin leads to inactivation of the Ca2+/Mg2+ ATPase and to comparable inhibition of 45Ca2+ transport. Ruthenium red and ouabain have no effect on either of these activities. Nigericin in the presence of external K+ is a potent inhibitor of 45Ca2+ translocation, whereas gramicidin activates transport. The proton translocator carbonylcyanide p-trifluoromethoxy-phenylhydrazone (FCCP) and FCCP + the ionophore valinomycin partially inhibit 45Ca2+ transport. By contrast, the above ionophores do not affect Ca2+/Mg2+ ATPase activity. Tentative mechanisms for ATP-dependent Ca2+ transport into cholinergic synaptic vesicles and the physiological significance of this process are discussed.

Acetylcholine↗
PubMed1980

Purification and characterization of synaptic vesicles from the electric organ of Torpedo ocellata.

Highly purified synaptic vesicles have been isolated from the electric organ of Torpedo ocellata by a rapid procedure which enables the concurrent isolation of synaptic vesicles and of intact presynaptic nerve endings (synaptosomes). The purification procedure consists of homogenization of fresh electric tissue in iso-osmotic glycine in the presence of EGTA, differential and density gradient centrifugation, and gel permeation on a glass beads column of 2500 a pore size. The purity of the vesicles was evaluated both biochemically and morphologically. The vesicles contain acetylcholine (ACh) and ATP in a ratio of 3:1 and at specific concentrations of 2,100nmol ACh/mg protein and 1,010nmol ACh/mg phospholipid. They are associated with Ca+2/Mg+2 ATPase activity and are devoid of the ouabain sensitive Na+/K+ ATPase. The relatively high yields as well as the short preparation time (about 9h for the vesicles and 4h for the synaptosomes) enables the employment of large samples of the isolated material on the day of preparation.

Acetylcholine↗
PubMed1980

On the regulation of acetylcholine release: a study utilizing Torpedo synaptosomes and synaptic vesicles.

1. Addition of ATP to isolated highly purified Torpedo synaptic vesicles results in 45Ca2+ uptake. 2. Ca2+ dependent ACh release from Torpedo synaptosomes is accompanied by the phosphorylation of a specific protein with an apparent subunit molecular weight of about 100,000 (band alpha). 3. Activation of the presynaptic muscarinic receptors by an agonist inhibits Ca2+-dependent ACh release from Torpedo synaptosomes. This process seems to be mediated through an interference with the phosphorylation of the band alpha protein, and not by blocking the voltage-dependent presynaptic Ca2+ channel.

Acetylcholine↗
PubMed1973

Separation and Ultrastructure of Proplastids from Dark-grown Euglena Cells.

A procedure for the separation of proplastids free of mitochondria from dark-grown Euglena cells has been developed. A fraction enriched in proplastids was used for freeze-etching study of proplastid structure. The prolamellar body in freeze-etched replicas appeared sponge-like, with thylakoids, often vesicular, emerging from it. The prolamellar body and the thylakoids were covered by particles of about 100A in diameter. No larger particles, typical of light-grown chloroplasts, were observed.

Journal Article↗