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Biomedical subjects

M Lieberman

Publications and source records attributed to M Lieberman.

At least 181 records · Page 10Linked to original sources
PubMed1977

Genetic control of radiation leukemia virus-induced tumorigenesis II. Influence of Srlv-1, a locus not linked to H-2.

A single locus, tentatively denoted Srlv-1 (susceptibility to radiation leukemia virus [RadLV]-1), confers dominant susceptibility to RadLV-induced leukemogenesis. Srlv-1 is not linked to H-2, and appears to be distinct from Fv-1 and Fv-2. Preliminary data suggest that Srlv-1 affected virus proliferation. A striking feature of this system is that Srlv-1 overrides the protection afforded by the H2D-associated dominant resistance to RadLV-induced neoplasia.

Animals↗
PubMed1977

Growth orientation of heart cells on nylon monofilament. Determination of the volume-to-surface area ratio and intracellular potassium concentration.

A new method is described for orienting the growth of embryonic chick heart cells as thin annuli about nylon monofilament. Analytical measurements of cell water, intracellular potassium, cell volume, and cell surface area incorporate several new techniques and provide the quantitative basis for characterizing the respective cell types in the preparation. The measurements support the hypothesis that tissue culture methodology does not alter the morphological and physiological properties of cardiac muscle cells. The preparations are ideally suited for radiotracer studies since tissue mass can be increased while retaining a relatively short diffusional distance.

Animals↗
PubMed1977

Compartmental analysis of potassium efflux from growth-oriented heart cells.

Radioisotopic flux studies were initiated with a new preparation of growth-oriented heart cells to determine the contribution of heterogeneous cell types and the limitations of extracellular diffusion in quantitating the passive movement of potassium ions. The efflux of potassium-42 from contractile preparations, which contain two populations of cells, cardiac muscle and fibroblastlike, could be resolved into two components similar to that described for naturally occurring preparations of cardiac muscle. Compartmental analysis of the efflux data, using analog and digital computational methods, resolved the tracer kinetics into a slow compartment (k=0.015 min-1) associated with fibroblastlike cells and a fast compartment (k=0.067 min-1) associated with the cardiac muscle cells. The rate constants derived from compartmental analysis were independent of tracer equilibration and preparation dry weight. Analytical measurements of the preparations provided a quantitative basis for determing the transmembrane potassium fluxes from the tracer kinetics. Cardiac muscle cells stimulated at a rate of 150 min-1 in the presence of 5.4 mM external potassium were found to have a potassium efflux of 15.7 pmoles cm-2sec-1 whereas the value obtained for the fibroblastlike cells was 1.88 pmoles cm-2sec-1. Diffusional limitations of 42K efflux were analyzed for several important variables which can affect isotopic reflux, namely, transmembrane flux, cell volume-to-surface area and cell packing fraction.

Animals↗
PubMed1977

Cutaneous herpes simplex virus infection of guinea pigs as a model for antiviral chemotherapy.

The kinetics of Herpesvirus hominis (Type 1) replication and lesion development in guinea pig skin were determined. The data indicate that lesion scores did not always reflect virus content. Virus replication was detected prior to appearance of lesions and maximum virus content preceded maximum lesion score. Lesions resolved slowly while virus content declined rapidly to an undetectable level. The utility of the guinea pig skin-herpesvirus model for the evaluation of ara-A and kethoxal was studied. Ara-A treatment at three dose levels suppressed lesion development and at the two highest dose levels lesion development was delayed. Lesion virus content, when determined during the period of maximum virus replication, was not affected by treatment. Kethoxal markedly suppressed lesion development and virus growth. Aspects of this experimental model typify cutaneous herpes simplex disease of man. Studies designed to further assess its utility for evaluating antiviral drugs seem warranted.

Aldehydes↗
PubMed1977

The cylindrical cell with a time-variant membrane resistance. Measuring passive parameters.

The passive electrical properties of a cable can be measured by injecting a step of current at a point and fitting the resulting potentials at several positions along the cable with analytic solutions of the cable equation. An error analysis is presented for this method (which is based on constant membrane resistance) when the membrane resistance is not constant, but increases linearly with time. The increase of rm produces a "creep" in the membrane potential at long times, as observed in cardiac, skeletal, and smooth muscle. The partial differential equation describing the time-varying cable was solved numberically for a step of current and these "data" were fit by standard constant-resistance methods. Comparing the resulting parameter values with the known true values, we suggest that a correction of the standard methods is not satisfactory for resistance changes of the kind observed; instead, the cable equation must be solved again for the particular form of rm(t). The practical implementation of a method by Adrian and Peachey for measuring the membrane capacitance and an approximate method for estimating the rate-of-change of membrane resistance are discussed in appendices.

Animals↗
PubMed1977

Inhibitory effect of a rhizobitoxine analog on bud growth after release from dormancy.

Application of the ethoxy analog of rhizobitoxine (l-2-amino-4-[2'-aminoethoxy]-trans-3-butenoic acid), an inhibitor of ethylene biosynthesis, inhibited growth of apple, crabapple, and apricot buds released from dormancy by chilling or by treatment with benzyladenine. When tea crabapple (Malus hupehensis [Pamp.] Rehd.) buds were sprayed once with 8.8 x 10(-3)m benzyladenine, ethylene production by the buds increased significantly 24 to 48 hours after benzyladenine treatment. Application of the rhizobitoxine analog to the buds at the time of benzyladenine treatment reduced ethylene evolution to the level of the controls for up to 2 weeks after treatment. Increase in bud weight was inhibited also but to a lesser extent. These data suggest that growth of buds is accompanied by ethylene production and that the inhibition of ethylene biosynthesis also inhibits bud growth. Since additional metabolic effects result from the action of the rhizobitoxine analog, no firm conclusions on its role can be drawn at this time.

Journal Article↗
PubMed1977

Influence of Plant Hormones on Ethylene Production in Apple, Tomato, and Avocado Slices during Maturation and Senescence.

Ethylene production by tissue slices from preclimacteric, climacteric, and postclimacteric apples was significantly reduced by isopentenyl adenosine (IPA), and by mixtures of IPA and indoleacetic acid, and of IPA, indoleacetic acid, and gibberellic acid after 4 hours of incubation. Ethylene production by apple (Pyrus malus L.) slices in abscisic acid was increased in preclimacteric tissues, decreased in climacteric peak tissues, and little affected in postclimacteric tissues. Indoleacetic acid suppressed ethylene production in tissues from preclimacteric apples but stimulated ethylene production in late climacteric rise, climacteric, and postclimacteric tissue slices. Gibberellic acid had less influence in suppressing ethylene production in preclimacteric peak tissue, and little influenced the production in late climacteric rise, climacteric peak, and postclimacteric tissues. IPA also suppressed ethylene production in pre- and postclimacteric tissue of tomatoes (Lycopersicon esculentum) and avocados (Persea gratissima). If ethylene production in tissue slices of ripening fruits is an index of aging, then IPA would appear to retard aging in ripening fruit, just as other cytokinins appear to retard aging in senescent leaf tissue.

Journal Article↗
PubMed1977

Methionine-induced Ethylene Production by Penicillium digitatum.

Shake cultures, in contrast to static cultures of Penicillium digitatum grown in liquid medium, were induced by methionine to produce ethylene. The induction was concentration-dependent, and 7 mM was optimum for the methionine effect. In the presence of methionine, glucose (7 mM) enhanced ethylene production but did not itself induce ethylene production. The induction process lasted several hours, required the presence of viable mycelium, exhibited a lag period for ethylene production, and was effectively inhibited by cycloheximide and actinomycin D. Thus, the methionine-induced ethylene production appeared to involve induction of an enzyme system(s). Methionine not only induced ethylene production but was also utilized as a substrate since labeled ethylene was produced from [(14)C]methionine.Following induction by the fungus, filtrates of induced shake cultures also evolved ethylene in increasing amounts by both enzymic and monenzymic reactions. Tracer experiments indicated that the ethylene released by the filtrate was derived from a fungal metabolite of methionine and not directly from methionine.

Journal Article↗
PubMed1977

Localization of the Ethylene-synthesizing System in Apple Tissue.

Apple (Malus sp.) slices gradually lost the ability to synthesize ethylene when incubated with a mixture of enzymes that digest cell walls. The released protoplasts did not produce ethylene. The release of protoplasts was faster from climacteric fruit slices than from preclimacteric tissue. In protoplast suspension culture, as new cell wall was deposited (as judged by the intensity of fluorescence of regenerating protoplasts stained with Calcofluor White and the incorporation of labeled myo-inositol into their ethanol-insoluble residue), ethylene synthesis was gradually regained. Restored ethylene synthesis reached a maximum after 80 hours in protoplasts from preclimacteric fruit and in 120 hours in those from climacteric tissue. Addition of methionine (1 mm) to the culture medium was essential for appreciable synthesis of ethylene; and this synthesis was inhibited by the aminoethoxy analogue of rhizobitoxine and by propyl gallate, inhibitors of ethylene synthesis in higher plants. We suggest that the ethylene-synthesizing enzyme system is highly structured in the apple cell and is localized in a cell wall-cell membrane complex.

Journal Article↗
PubMed1976

The role of lymphoid and haematopoietic target cells in viral lymphomagenesis of C57BL/Ka mice. I. Susceptibility to viral replication.

The influence of several parameters on the capacity of C57BL/Ka mouse haematopoietic cells to support replication of the radiation leukemia virus (RadLV) has been examined. Although replication of the virus is strongly thymotropic, the bone marrow and spleen are also susceptible when infection is initiated at birth rather than in adult life. Irradiation transiently restores the susceptibility of adults almost to the neonatal level. Neonatal thymectomy does not diminish the capacity of marrow cells to support virus replication, indicating that the migration of infected thymus cells back to the marrow is not responsible for the observed effect. Bone marrow cells in which viral antigens are no longer detectable yield infectious virus after intrathymic inoculation, suggesting the existence of a cryptic state of virus infection.

Animals↗
PubMed1976

Biological and serological characterization of radiation leukemia virus.

Radiation leukemia virus, isolated from radiation-induced lymphomas in C57BL/Ka mice and propagated in that strain, is thymotropic and leukemogenic in vivo but replicates poorly, if at all, in mouse and mink fibroblast cultures in vitro. Comparative studies indicate that this naturally occurring virus is distinct from the previously recognized classes of endogenous murine ecotropic and xenotropic C-type viruses which are capable of replication on fibroblasts (fibrotropic) but are neither thymotropic nor leukemogenic. These studies also demonstrate that a differentiation-specific restriction system governing the replication of the murine ecotropic C-type viruses operates in addition to the previously defined Fv-1 and SRV gene restriction systems.

Animals↗
PubMed1976

Test construction.

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Anesthesiology↗