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Biomedical subjects

M Lieberman

Publications and source records attributed to M Lieberman.

At least 163 records · Page 9Linked to original sources
PubMed1979

Production and action of ethylene in senescing leaf discs: effect of indoleacetic Acid, kinetin, silver ion, and carbon dioxide.

Supraoptimal concentrations of indoleacetic acid (IAA) stimulated ethylene production, which in turn appeared to oppose the senescence-retarding effect of IAA in tobacco leaf discs. Kinetin acted synergistically with IAA in stimulating ethylene production, but it inhibited senescence. Silver ion and CO(2), which are believed to block ethylene binding to its receptor sites, delayed senescence in terms of chlorophyll loss and stimulated ethylene production. Both effects of Ag(+) were considerably greater than those of CO(2). IAA, kinetin, CO(2), and Ag(+), combined, acted to increase ethylene production further. Although this combination increased ethylene production about 160-fold over that of the control, it inhibited senescence. Treatment with 25 mul/l of ethylene in the presence of IAA enhanced chlorophyll loss in leaf discs and inhibited by about 90% the conversion of l-[3,4-(14)C] methionine to (14)C(2)H(4) suggesting autoinhibition of ethylene production.The results suggest that ethylene biosynthesis in leaves is controlled by hormones, especially auxin, and possibly the rate of ethylene production depends, via a feedback control system, on the rates of ethylene binding at its receptor sites.

Journal Article↗
PubMed1979

Potassium permeability of embryonic avian heart cells in tissue culture.

The relationship between the external potassium concentration ([K]o) and membrane permeability has been reexamined using a tissue-cultured preparation of embryonic chick heart cells in which diffusional limitations are minimal. The unidirectional K efflux and electrochemical gradients were determined as a function of [K]o, and the results showed that potassium permeability was constant within the range of 1-20 mM [K]o. Membrane potentials were obtained in K-free solutions and correlated with 42K efflux and intracellular ion content measurements under the same conditions. In contrast to preparations of the intact embryonic chick heart, 42K efflux does not decrease in K-free media. Simulations of tracer measurements at reduced [K]o from naturally occurring cardiac muscle indicate that the experimentally observed decrease in 42K efflux could result from diffusional limitations. This observation, when coupled with the experimental results, suggests that the effect of low [K]o on membrane permeability in homeothermic preparations of cardac muscle should be reevaluated.

Animals↗
PubMed1979

In vivo infectivity of the fibrotropic C-type viral isolates from C57BL/Ka mice.

Of the three fibrotropic C-type viral isolates from C57BL/Ka mice, only the BL/Ka(B) virus is capable of infecting normal hematopoietic and lymphoid cell populations of C57BL/Ka mice in vivo, and none are tumorigenic. Inoculation of this virus alone into neonates resulted in transient replication in the bone marrow, spleen, and occasionally the thymus. Thymocytes could, however, be permanently infected in such animals if BL/Ka(B) were coinoculated with the xenotropic BL/Ka(X) virus. Neonatal injection of BL/Ka(B) prior to fractionated wholebody irradiation yielded an increase in the percentage of virus-productive radiogenic lymphomas and a decrease in incidence of such tumors. Injection of BL/Ka(B) into normal adult C57BL/Ka mice did not yield overt expression of virus replication in any of the tissues tested; latent infection could, however, be detected in the marrow and in the reticuloepithelium of the thymus. Whole-body X-irradiation of adults with 400 rads partially restored the neonatal susceptibility of bone marrow cells to infection by the isolate. BL/Ka(B) injection after fractionated whole-body irradiation of weanling C57BL/Ka mice increased the percentage of virus-positive lymphomas and revealed that a bone marrow cell subpopulation permissive for infection by the virus increases greatly in abundance soon after irradiation.

Animals↗
PubMed1978

T-cell lymphoma induction by radiation leukemia virus in athymic nude mice.

We report the development of extrathymic lymphoblastic lymphomas in RadLV-inoculated congenitally athymic nude mice. Thus, a leukemogenic virus which appears to require the presence of a thymus for its replication in normothymic mice can infect and transform target cells in the absence of this organ in the athymic host. The cells of one of these lymphomas have been established in vitro as a permanent cell line, BALB/Nu1. This cell line as well as a lymphoma induced in NIH/Swiss nude mice exhibit several T-cell markers, including terminal deoxynucleotidyl transferase activity, Thy-1.2, and Ly-2.2, but not Ly-1.2 nor TL. Ig determinants were not detected. The characteristics of the tumor cells support the view that cells with T-cell markers may normally exist in nude mice and undergo neoplastic transformation and clonal expansion after infection with a leukemogenic virus. The alternative possibility that virus-induced differentiation of prothymocytes may lead to the expression of Thy-1.2 and Ly-2.2 antigens is also considered. BALB/Nu1 cells release large numbers of type C viral particles. The virus, designated radiation leukemia virus (RadLV)/Nu1, has RTase activity and the protein profile characteristic of murine leukemia virus (MuLV). In radioimmunoassays, it cross-reacts completely with RadLV/VL3, a virus obtained from RadLV-induced C57BL/Ka thymic lymphoma cells in culture, and slightly with a xenotropic virus (BALB:virus-2) and with AKR MuLV. On inoculation into C57BL/Ka mice it has thymotropic and leukemogenic activity. In vitro it is B-tropic, poorly fibrotropic, and has limited xenotropic activity. Thus, RadLV/Nu1 appears to be biologically and serologically similar or identical to its parent virus, RadLV.

Animals↗
PubMed1978

Increased synthesis and expression of H-2 antigens on thymocytes as a result of radiation leukemia virus infection: a possible mechanism for H-2 linked control of virus-induced neoplasia.

Previous studies from this laboratory have mapped resistance and/or susceptibility to radiation-induced leukemia virus (RadLV)-induced neoplasia to the H-2D region. H-2 linked effects on virus replication can be detected subsequent to the initial virus infection, and clear-cut differences in numbers of virus infected thymus cells can be detected as early as 5 wk after RadLV inoculation. Rapid increases in cellular synthesis and cell surface expression of H-2 antigens are detectable immediately after virus inoculation. These changes have been studied by immunofluorescence, absorption, cell surface iodination followed by sodium dodecyl-sulfate-polyacrylamide gel electrophoresis, and two dimensional gel electrophoretic analysis of internally labeled lymphocyte proteins. Expression of H-2K molecules is significantly increased in cells of susceptible and resistant animals. However, significant increases in expression of H-2D antigens occurs only on thymus cells from resistant strains (H-2Dd). Transformed cells of resistant and susceptible H-2 haplotypes adapted to tissue culture lack detectable H-2 antigens as determined by serological absorption studies. It is argued that altered expression of H-2 antigens plays a very significant role in the mechanism of host defense to virus infection.

Animals↗
PubMed1978

Inhibition of Ethylene Production in Penicillium digitatum.

Production of ethylene by static cultures of Penicillium digitatum, which utilize glutamate and alpha-ketoglutarate as ethylene precursors, was inhibited by methionine, methionine sulfoxide, methionine sulfone, and methionine sulfoximine. Rhizobitoxine did not affect ethylene production but its ethoxy and methoxy analogues were effective inhibitors of ethylene production; its saturated methoxy analogue and kainic acid stimulated ethylene production. Tracer studies showed that the inhibitors blocked the conversion of [(3)H]glutamate into [(3)H]ethylene.In shake cultures of this fungus, which utilize methionine as the ethylene precursor, rhizobitoxine and its unsaturated analogues all inhibited, while the saturated methoxy analogue stimulated ethylene production. In both types of cultures inhibition was irreversible and was diminished by increasing concentrations of the ethylene precursor. The inhibitory activity or lack of it by rhizobitoxine and its analogues appears to be a function of their structural resemblance to glutamate and methionine as well as of their size and stereoconfiguration. These data suggest similarities between the ethylene-forming system in the fungus and in higher plants despite differences in precursors under some cultural conditions.

Journal Article↗
PubMed1978

Inhibition of ethylene production in fruit slices by a rhizobitoxine analog and free radical scavengers.

The rhizobitoxine analog, L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid (Ro), which effectively inhibits ethylene production in apple (Malus domestica Borkh.) and other tissues at concentrations at about 68 micromolar, inhibited ethylene production by about 50 to 70% in green tomato (Lycopersicon esculentum Mill.) fruit slices but only by about 15% in pink and ripe tomato tissue slices. Ethylene production in climacteric-rise and postclimacteric avocado slices was likewise relatively insensitive to 68 micromolar Ro. At 340 micromolar Ro, inhibition of ethylene production increased up to 50% in pink tomato slices, whereas 680 micromolar Ro was required to inhibit ethylene production by 30% in avocado slices. Incorporation of (14)C from [(14)C]methionine into ethylene in green and pink tomato tissues was inhibited by Ro to about the same extent as inhibition of total ethylene production. Results thus far are inconclusive as to the mechanism of Ro resistance in tomato and avocado tissues. At 1 millimolar, free radical scavengers such as benzoate, propyl gallate, nordihydroguaiaretic acid, and to a lesser extent, eugenol, inhibited ethylene production in both Ro-sensitive (green tomato and apple) tissues and Ro-resistant (pink tomato and avocado) tissues. Therefore, free radical steps are suggested in the ethylene-forming systems.

Journal Article↗
PubMed1978

Specificity of cell surface virus receptors on radiation leukemia virus and radiation-induced thymic lymphomas.

We have developed a system for analysis of murine leukemic virus (MuLV) receptors on the surface of thymic lymphoma cells utilizing the fluorescence-activated cell sorter. The binding of fluoresceinated or rhodaminated MuLV to target cells showed saturation kinetics and was blocked by homologous MuLV, and bound MuLV had a polypeptide profile identical to that of input MuLV. Thymic lymphomas bound specifically the MuLV which induced them, whereas only 0.5 to 2% of normal thymocytes showed equivalent MuLV binding. Simultaneous binding of excess fluoresceinated RadLV and rhodaminated MCF-247 AKR virus to radiation leukemia virus-induced or spontaneous AKR thymic lymphomas demonstrated that even in the presence of both viruses the cells bound preferentially the inducing MuLV. Examination of the C57BL/Ka endogenous viruses showed that radiation leukemia virus-induced thymic lymphomas bind only thymotropic-leukemogenic radiation leukemia virus and not eco- or xenofibrotropic MuLV's. Thus, virus binding in this system involves only leukemogenic isolates of these retroviruses and implies a central role of this receptor-ligand interaction in the processes of leukemic transformation.

Cell Line↗
PubMed1978

The role of orthodontics as an adjunct to periodontal therapy.

In the formulation of a treatment plan for patients with advanced periodontal disease, the benefits that orhtodontics can supply must be considered. By improving the position of malposed teeth, a better environment is created for the health of the gingivae and attachment apparatus, as well as the possibility to improve osseous defects as the result of orthodontically stimulated osteogenic activity. The ultimate goal of treatment must be, in addition to control of inflammation, plaque and trauma, the creation of optimal morphologic and functional conditions which will allow these objectives to be attained. This will provide the prosthodontist and periodontist with a better chance to prolong the life of the dention.

Adult↗
PubMed1978

Macrophage-mediated in vitro sensitization of lymphocytes. II. The detection of neo-antigens on transformed lymphocytes and passages of normal fibroblasts.

Unprimed lymphocytes were sensitized in vitro by incubating them with syngeneic macrophages that had been fed with viral or cellular antigens. The sensitized lymphocytes were tested for their cytotoxic activity against virus-infected and noninfected fibroblasts. The antigenic preparations used for priming the macrophages were either tumor cell-free extracts or supernatants from virus productive cells. Cell-free extracts from the productive RadLV-induced lymphoma cells or the nonproductive radiation-induced lymphoma cells were immunogenic when presented to lymphocytes by macrophages. In contrast, cell-free extracts from normal thymocytes were much less immunogenic, suggesting that the presence of viral associated antigens (VAA) can selectively be detected on lymphoma cells by this assay. Fibroblastic cell lines but not primary fibroblasts were also susceptible to the cytotoxic lymphocytes induced by RadLV-fed macrophages. Primary fibroblasts became susceptible to the sensitized lymphocytes either after infection with the corresponding virus, or if not infected, after several passages in vitro, suggesting that neo-antigens cross-reacting with viral antigens appear during sub-culturing of fibroblasts in vitro. This system makes it possible to detect VAA either as immunogens when presented to lymphocytes by macrophages, or as targets for cytotoxic lymphocytes.

Animals↗