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Biomedical subjects

M Lieberman

Publications and source records attributed to M Lieberman.

At least 127 records · Page 7Linked to original sources
PubMed1983

Three-dimensional configuration of the mitochondria in cultured heart cells.

The mitochondria of chick heart cells grown in monolayer culture occupy a relatively large percentage (30%) of the cell cytoplasmic volume, as determined by thin section morphometry, and vary in their ultrastructural configuration in response to different functional states of the cell. The present study was undertaken to determine the three-dimensional structure of the mitochondria in cardiac cells, since reconstruction experiments have demonstrated the existence of a mitochondrial network in cardiac and other tissues, e.g. diaphragm, soleus and vastus muscle, kidney and urinary bladder, in vivo. Confluent monolayers of synchronously beating embryonic chick heart cells were fixed, stained with a mitochondria-specific heavy metal complex (Pb-Cu citrate), and processed for either transmission electron microscopy (TEM) or scanning electron microscopy (SEM) and backscatter electron imaging (BSI). Both secondary and backscatter images revealed the presence of many thin, extremely elongate structures which in stereo views appeared as branching, anastomosing networks. TEM demonstrated localization of the electron dense stain to either nuclear or mitochondrial membranes, structures which were easily distinguished with SEM or BSI alone. These morphological results indicate that many mitochondria of the cultured heart muscle cell are interconnected and suggest that this morphological network may represent a parallel functional unit which maintains the energy state of the cell.

Animals↗
PubMed1982

Biosynthesis of ethylene from methionine in aminoethoxyvinylglycine-resistant avocado tissue.

This study was conducted to determine if aminoethoxyvinylglycine (AVG) insensitivity in avocado (Persea americana Mill., Lula, Haas, and Bacon) tissue was due to an alternate pathway of ethylene biosynthesis from methionine. AVG, at 0.1 millimolar, had little or no inhibitory effect on either total ethylene production or [(14)C] ethylene production from [(14)C]methionine in avocado tissue at various stages of ripening. However, aminoxyacetic acid (AOA), which inhibits 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (the AVG-sensitive enzyme of ethylene biosynthesis), inhibited ethylene production in avocado tissue. Total ethylene production was stimulated, and [(14)C]ethylene production from [(14)C]methionine was lowered by treating avocado tissue with 1 millimolar ACC. An inhibitor of methionine adenosyltransferase (EC 2.5.1.6), l-2-amino-4-hexynoic acid (AHA), at 1.5 millimolar, effectively inhibited [(14)C]ethylene production from [(14)C]methionine in avocado tissue but had no effect on total ethylene production during a 2-hour incubation. Rates of [(14)C]AVG uptake by avocado and apple (Malus domestica Borkh., Golden Delicious) tissues were similar, and [(14)C]AVG was the only radioactive compound in alcohol-soluble fractions of the tissues. Hence, AVG-insensitivity in avocado tissue does not appear to be due to lack of uptake or to metabolism of AVG by avocado tissue. ACC synthase activity in extracts of avocado tissue was strongly inhibited (about 60%) by 10 micromolar AVG. Insensitivity of ethylene production in avocado tissue to AVG may be due to inaccessibility of ACC synthase to AVG. AVG-resistance in the avocado system is, therefore, different from that of early climacteric apple tissue, in which AVG-insensitivity of total ethylene production appears to be due to a high level of endogenous ACC relative to its rate of conversion to ethylene. However, the sensitivity of the avocado system to AOA and AHA, dilution of labeled ethylene production by ACC, and stimulation of total ethylene production by ACC provide evidence for the methionine --> SAM --> ACC --> ethylene pathway in avocado and do not suggest the operation of an alternate pathway.

Journal Article↗
PubMed1982

Influence of calcium and magnesium on ethylene production by apple tissue slices.

The decline in ethylene production in apple (Pyrus malus L. cv. Golden Delicious) tissue slices during 24 hours incubation in 600 millimolar sorbitol and 10 millimolar 2-(N-morpholino)ethanesulfonic acid buffer (pH 6.0) is recognized as a senescent phenomenon. The inclusion of very high concentrations (100 millimolar) of Ca(2+), Mg(2+), or Ca(2+) plus Mg(2+) severely inhibited ethylene production during the first 6 hours of incubation. However, after 6 hours and up to 24 hours the ethylene-forming system was stablized. These high concentrations of Ca(2+), Mg(2+), or Ca(2+) plus Mg(2+) virtually eliminated lipid peroxidation and protein leakage from these slices. Also conversion of 1-aminocyclopropane-1-carboxylic-1-acid to ethylene and the influence of indoleacetic acid on ethylene production was stabilized after 24 hours of incubation by these high concentrations of Ca(2+), Mg(2+), and Ca(2+) plus Mg(2+). Addition of divalent ionophores severely inhibited ethylene production, but this inhibition was prevented by Ca(2+) in concentrations greater than the ionophore. These data suggest that the loss of ethylene production by aging tissue slices results from degradation of membranes. They support previous work that indicates that the ethylene-forming system, perhaps the segment of the pathway from 1-aminocyclo-propane-1-carboxylic-1-acid to ethylene, resides in the plasma membrane.

Journal Article↗
PubMed1982

Recycling of 5'-methylthioadenosine-ribose carbon atoms into methionine in tomato tissue in relation to ethylene production.

The ribose moiety of 5'-methylthioadenosine (MTA) is metabolized to form the four-carbon unit (2-aminobutyrate) of methionine in tomato tissue (Lycopersicon esculentum Mill., cv. Pik Red). When [U-(14)C-adenosine] MTA was administered to tomato tissue slices, label was recovered in 5-methylthioribose (MTR), methionine, 1-aminocyclopropane-1-carboxylic acid (ACC), C(2)H(4) and other unidentified compounds. However, when [U-(14)C-ribose]MTR was administered, radioactivities were recovered in methionine, ACC and C(2)H(4), but not MTA. This suggests that C(2)H(4) formed in tomato pericarp tissue may be derived from the ribose portion of MTA via MTR, methionine and ACC. The conversion of MTR to methionine is not inhibited by aminoethoxyvinylglycine (AVG), but is O(2) dependent. These data present a new salvage pathway for methionine biosynthesis which may be important in relation to polyamine and ethylene biosynthesis in tomato tissue.

Journal Article↗
PubMed1982

Inhibition by polyamines of macromolecular synthesis and its implication for ethylene production and senescence processes.

Applied diamines and polyamines inhibited the incorporation of radioactively labeled leucine and uridine into trichloroacetic acid-insoluble material in apple (Malus domestica Borkh, cv Golden Delicious) fruit tissue. The inhibitory effect was in general more pronounced with the higher molecular weight amines. Putrescine at 5 millimolar inhibited leucine incorporation by 37% and uridine by 44%. Spermidine and spermine at the same concentration inhibited uridine incorporation by 60%. The polyamines at concentrations between 0.1 and 1.0 millimolar inhibited leucine incorporation by 55 to 90%. The inhibitory effect of 0.1 to 10 millimolar polyamines on dark- and wound-induced senescence or ethylene production, is discussed in the light of interference with macromolecular synthesis.

Journal Article↗
PubMed1982

Sodium tracer kinetics and transmembrane flux in tissue-cultured chick heart cells.

Considerable difficulty has been encountered in defining the physiological significance of sodium tracer kinetic measurements in cardiac muscle. In this study, 24Na+ efflux experiments were performed by directly monitoring tissue radioactivity during the superfusion of growth-oriented embryonic chick heart cells in tissue cultured. The cellular 24Na+ efflux from contractile preparations exhibited at least two exponential components whereas noncontractile, fibroblastlike preparations had a single efflux component similar in rate to the slower component of the contractile preparations. We concluded that the slow component represents efflux from nonmuscle cells, whereas the faster component reflects the muscle cell compartment. The mean Na+ efflux rate constants for contractile preparations (beating 150 min-1) were 3.1 and 0.35 min-1. Intracellular Na+ concentrations, as determined by isotope uptake and by flame photometry, were 18 and 16 mM for contractile and nonmuscle preparations, respectively. The steady-state, transmembrane fluxes are 98 and 5 pmol . cm-2 . s-1 for muscle and nonmuscle cells, respectively. The Na+ efflux kinetics in 10(-4) M ouabain were reduced by approximately 16% from the control value. These findings indicate that the greater part of the steady-state Na+ efflux in cultured heart cells is due to mechanisms other than the Na+-K+ pump.

Animals↗
PubMed1982

Delivery of the second twin.

A retrospective chart review of all twin deliveries between April 1, 1977, and March 20, 1980, at the Boston City Hospital and the Brigham and Women's Hospital revealed corrected neonatal mortality rates of 0 for 74 twins in nonvertex presentation delivered by cesarean section and 0 for 76 second-born twins extracted vaginally. Breech extraction of 76 second-born twins weighing more than 1499 g at birth was not associated with a statistically significant increase in the incidence of 5-minute Apgar scores of 7 or less when compared to 74 similarly asymptomatic twins in nonvertex presentation delivered by cesarean section. Vaginal delivery may be considered when the second twin, weighing more than 1500 to 2000 g, is in breech presentation.

Apgar Score↗
PubMed1981

Linear electrical properties of passive and active currents in spherical heart cell clusters.

Impedance studies were performed on small spherical clusters of embryonic chick heart cells grown in tissue culture. Each syncytial cluster was impaled with two microelectrodes; one injected low amplitude stochastic current and the other recorded the resulting perturbation of intracellular potential. The current and potential records were digitized, decomposed into their sinusoidal components, and the frequency domain impedance of the cluster was determined. The impedance data were compared with a theory for current flow in a spherical syncytium and values were derived for parameters describing the membranes and intercellular clefts of the tissue. The clusters were spontaneously active but usually became temporarily quiescent when impaled with two electrodes. The potential stabilized at a value close to -30 mV. At this depolarized potential, active slow currents, presumably present in the cardiac action potential, contributed noticeably to the linear impedance, producing a resonant peak in the magnitude of the impedance at a frequency of 1-3 Hz. The linearized impedance functions for these currents were characterized in the presence and absence of tetrodotoxin (TTX) and D-600. TTX had no noticeable effect on the impedance but D-600 essentially abolished the active currents. Although the ionic basis of these currents is not known, frequency domain analysis appears to be a viable technique for studying slow currents in heart muscle.

Animals↗
PubMed1981

Inhibition of the Conversion of 1-Aminocyclopropane-1-carboxylic Acid to Ethylene by Structural Analogs, Inhibitors of Electron Transfer, Uncouplers of Oxidative Phosphorylation, and Free Radical Scavengers.

Cyclopropane carboxylic acid (CCA) at 1 to 5 millimolar, unlike related cyclopropane ring analogs of 1-aminocyclopropane-1-carboxylic acid (ACC) which were virtually ineffective, inhibited C(2)H(4) production, and this inhibition was nullified by ACC. Inhibition by CCA is not competitive with ACC since there is a decline, rather than an increase, in native endogenous ACC in the presence of CCA. Similarly, short-chain organic acids from acetic to butyric acid and alpha-aminoisobutyric acid inhibited C(2)H(4) production at 1 to 5 millimolar and lowered endogenous ACC levels. These inhibitions, like that of CCA, were overcome with ACC. Inhibitors of electron transfer and oxidative phosphorylation effectively inhibited ACC conversion to C(2)H(4) in pea and apple tissues. The most potent inhibitors were 2,4-dinitrophenol (DNP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) which virtually eliminated ACC-stimulated C(2)H(4) production in both tissues. Still other inhibitors of the conversion of ACC to C(2)H(4) were putative free radical scavengers which reduced chemiluminescence in the free radical-activated luminol reaction. These inhibitor studies suggest the involvement of a free radical in the reaction sequence which converts ACC to C(2)H(4). Additionally, the potent inhibition of this reaction by uncouplers of oxidative phosphorylation (DNP and CCCP) suggest the involvement of ATP or the necessity for an intact membrane for C(2)H(4) production from ACC. In the latter case, CCCP may be acting as a proton ionophore to destroy the membrane integrity necessary for C(2)H(4) production.

Journal Article↗
PubMed1981

Some Characteristics of the System Converting 1-Aminocyclopropane-1-carboxylic Acid to Ethylene.

The rate of C(2)H(4) production in plant tissue appears to be limited by the level of endogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous ACC stimulated C(2)H(4) production considerably in plant tissues, but this required 10 to 100 times the endogenous concentrations of ACC before significant increases in C(2)H(4) production were observed. This was partially due to poor penetration of ACC into the tissues. Conversion of ACC to C(2)H(4) was inhibited by free radical scavengers, reducing agents, and copper chelators, but not by inhibitors of pyridoxal phosphate-mediated reactions. The system for converting ACC to C(2)H(4) may be membrane-associated, for it did not survive treatment with surface-active agents and cold or osmotic shock reduced the capacity of the system to convert ACC to C(2)H(4). The reaction rate was sensitive to temperatures above 29 and below 12 C, which suggests that the system may be associated with membrane-bound lipoproteins. The data presented support the possibility that the conversion of exogenous ACC to C(2)H(4) proceeds via the natural physiological pathway.

Journal Article↗
PubMed1981

Polyamines inhibit biosynthesis of ethylene in higher plant tissue and fruit protoplasts.

Ethylene production in apple fruit and protoplasts and in leaf tissue was inhibited by spermidine or spermine. These polyamines, as well as putrescine, inhibited auxin-induced ethylene production and the conversion of methionine and 1-aminocyclopropane-1-carboxylic acid to ethylene. Polyamines were more effective as inhibitors of ethylene synthesis at the early, rather than at the late, stages of fruit ripening. Ca(2+) in the incubation medium reduced the inhibitory effect caused by the amines. A possible mode of action by which polyamines inhibit ethylene production is discussed.

Journal Article↗
PubMed1981

Phenotypic characterization of mice of thymus target cells susceptible to productive infection by the radiation leukemia virus.

The spread of virus replication was studied by electron microscopy in the thymuses of inbred C57BL/Ka mice after intrathymic inoculation of the radiation leukemia virus (RadLV). The first type C-budding virus particles appeared in scarce blast cells of the subcapsular zone. Most of these blast cells were "X-cells," i.e., the thymus lymphoid cells most actively engaged in DNA synthesis. Virus replication spread to the entire cortical blast cell population and, from day 7 on, to the small cortical lymphocytes. The first virus-producing cells were derived from a very few target cells (approximately 0.001-0.003% of thymocytes) susceptible to RadLV infection. For determination of the phenotypes of these target cells, various thymocyte subpopulations obtained through a battery of cell separation methods were tested for their ability to support the replication of RadLV/VL3 virus in short-term culture. Most of these target cells were sensitive to the lytic effect of hydrocortisone and migrated in the fastest fraction of a 1Xg sedimentation gradient, together with the majority of [3H] thymidine-incorporating blast cells. They exhibited an intermediate density and expressed H-2 and Thy 1,2 cell surface antigens, although they were not found preferentially among the high Thy 1,2 population to which most of the cortical blast cells belonged. The spread of RadLV within the thymus and the surface phenotype characteristics of target cells indicate that these cells correspond to the thymocyte subset at the earliest stage of thymic lymphopoiesis and may be transitional between the prothymocytes and the subcapsular blast cell population.

Animals↗
PubMed1981

Macrophage and lymphocyte-depleted thymus reticuloepithelial cell cultures: establishment and functional influence on T-lymphocyte maturation, C-type virus expression and lymphomatous transformation in vitro.

A method of cultivation has been developed that yields thymus reticuloepithelial (TRE) cell monolayers composed almost entirely of epithelial-like cells, with no detectable macrophages or lymphocytes. These cultures show the capacity to induce responsiveness to lectin mitogens in immature thymocytes. Such monolayers induce Thy-1 expression in nude mouse spleen and bone marrow cells. The functional macrophage-lymphocyte depleted TRE monolayers can be cryptically infected by radiation leukemia virus (RadLV). However, RadLV-infected TRE cells lack the capacity to induce neoplastic transformation in normal weanling and newborn thymocytes. Cultures prepared from C57BL/Ka mice treated with a leukemogenic course of irradiation produce a B-fibrotropic nonleukemogenic virus, and normal thymocytes cocultivated with these monolayers do not undergo in vitro transformation. It is concluded that TRE monolayers depleted of macrophages and lymphocytes: (1) exhibit the functional capacity to induce some of the properties of mature T cells; (2) are infectable by RadLV; (3) are one of the sites for expression of ecotropic virus after leukemogenic fractionated irradiation; and (4) are not capable of transforming normal thymocytes in vitro.

Animals↗
PubMed1981

Marrow-thymus interactions during radiation leukemogenesis in C57BL/Ka mice.

Transplantation of thymus and bone marrow cells from irradiated C57BL/Ka mice demonstrated the presence of potentially neoplastic cells in the thymus at 30 to 60 days postirradiation. During the same interval, no such cells could be detected in the bone marrow; moreover, the capacity of bone marrow cells to repopulate the thymus was impaired severely. These observations suggest that the primary site of neoplastic transformation in irradiated C57BL/Ka mice is the thymus rather than the bone marrow and that impaired thymic regeneration is a critical step in radiation leukemogenesis in mice.

Animals↗
PubMed1980

Ultrasound-facilitated intrauterine transfusions.

Ultrasound-facilitated intrauterine transfusion was performed on 35 fetuses. Eleven fetuses were hydropic and less than 26 weeks' gestation at the time of the first intrauterine transfusion (IUT). Only two (18%) neonates survived. Twelve fetuses were not hydropic and less than 26 weeks' gestation at time of IUT. Six (50%) neonates survived. Corrected neonatal survival rates for three hydropic and nine nonhydropic fetuses transfused after 26 weeks were 100% and 78%, respectively. The presence of ascites documented by ultrasound is an adequate indication for an IUT and permitted earlier detection of sicker fetuses; however, as a therapeutic aid, ultrasound neither diminished the fetal morbidity and mortality associated with the procedure nor completely eliminated the need for radiography to confirm proper intra-abdominal localization of the transfusion tubing.

Ascites↗