bluuebunny/crossref_metadata_2025_split huggingface dataset:
Failure of tritiated thymidine incorporation into DNA to reflect the autoradiographically demonstrable calcium‐induced increase in thymic lymphoblast DNA synthesis
Authors: Youdale T. , Macmanus J. P. 
Published: February 2005

AbstractIncreasing the extracellular calcium concentration in thymic lymphocyte suspension from 0.6 to 1.8 mM stimulated the proliferation of the lymphoblast subpopulation as measured by increases in the proportion of cells autoradiographically labeled with 3H‐TdR and in mitotic activity. However it was not possible to show this increased DNA synthesis by scintillometric measurement of the amount of 3H‐TdR incorporated into extracted DNA. On the other hand, calcium did raise the incorporation of 14C‐formate into the thymine residues of DNA, and increased the activity of isolated thymocyte thymidylate synthetase. In contrast to the mitogenic calcium ion, a thymidylate synthetase inhibitor, methotrexate, actually increased the incorporation of 3H‐TdR into DNA.It is concluded that calcium increases the endogenous synthesis of thymidylate which in turn prevents the amount of incorporation of exogenous 3H‐TdR from accurately reflecting the true level of DNA synthesis.
Polyamine metabolism in a rat brain tumor cell line: Its relationship to the growth rate
Authors: Heby Olle , Marton Laurence J. , Wilson Charles B. , Martinez Hugo M. 
Published: February 2005

AbstractTo investigate whether the metabolism of the polyamines putrescine, spermidine and spermine is related to cellular growth rate, we have measured the activities of L‐ornithine decarboxylase and S‐adenosyl‐L‐methionine decarboxylase as well as the levels of the polyamines in rat brain tumor cells at various stages of a 7‐day in vitro growth period and correlated them with the continuous changes in specific growth rate ([dN[t]/dt]/N[t]). L‐Ornithine decarboxylase and S‐adenosyl‐L‐methionine decarboxylase both exhibited their maximal activities at the time of most rapid growth. A high positive correlation between the activities of these enzymes and the specific growth rate of the tumor cells during the entire growth period was demonstrated statistically. The pattern of fluctuation of the spermidine content during the culture cycle was similar to those of the enzyme activities and likewise showed a high positive correlation with the specific growth rate of the tumor cells during the entire growth period. The putrescine content exhibited a low positive correlation, whereas the spermine content exhibited a somewhat higher, but negative correlation with the specific growth rate.The high correlation between the specific growth rate of the tumor cells and the synthesis of the polyamines indicates that these events are primarily associated with processes involved in cell replication. Putrescine and spermidine are thought to participate in the regulation of cellular growth rate; a high content may augment, and a low content may restrain, cellular growth rate.
A mechanical dissociation method for preparation of muscle cell cultures
Authors: Tepperman Katherine , Morris Glenn , Essien Francine , Heywood Stuart M. 
Published: February 2005

AbstractA cell preparation method by which large numbers of embryonic chick skeletal muscle cells may be obtained is described. The procedure requires fewer manipulations and much less time than standard trypsinization. By the criteria used, both methods are comparable with respect to percent viable cells and survival of plated cells. However, in addition to the ease of preparation, the mechanical dissociation method offers the significant advantage that the cell suspension is greatly enriched for myoblasts without the necessity of an additional preplating step.
Effects of prolonged quiescence on nuclei and chromatin of WI‐38 fibroblasts
Authors: Rossini Mara , Lin Jung‐Chung , Baserga Renato 
Published: February 2005

AbstractDNA synthesis and cell division are markedly reduced in confluent mono‐layers of WI‐38 diploid fibroblasts, but resume again if the depleted medium is replaced by fresh medium containing 10% fetal calf serum. If the cells are kept quiescent for prolonged periods of time after confluence (1 or 2 weeks), the fraction of cells that can be stimulated to proliferate by fresh serum decreases and the length of the prereplicative phase increases. The template activity of isolated nuclei decreases with increasing time of quiescence, and parallel changes occur in chromatin as evidenced by circular dichroism spectra and capacity to bind the intercalating dye, ethidium bromide.When WI‐38 cells are stimulated to proliferate after prolonged quiescence, the increase in template activity of nuclei is delayed by several hours in comparison to cells stimulated after short periods of quiescence. Two distinct steps, both requiring serum, can be identified in the prereplicative phase of cells stimulated to proliferate after prolonged quiescence.We interpret the results as indicating that, during prolonged quiescence, WI‐38 fibroblasts go into a deeper G0 state from which they can be rescued only after prolonged stimulation. In this respect, prolonged quiescence may bear some resemblance to the process of aging.
Interrelationships between water and cellular metabolism in Artemia cysts IV. Adenosine 5′‐triphosphate and cyst hydration
Authors: Clegg James S. , Cavagnaro Joy 
Published: February 2005

AbstractThe concentration of ATP in cysts of the brine shrimp, Artemia salina, has been studied as a function of cyst hydration. Cysts dried over CaSO4 contain 0.02 gH2O/g cysts and 0.54 ± 0.05 (S.D.) m̈moles of ATP/g dried cysts. Addition of water up to 0.05 g/g cysts produced no net change in the level of ATP during incubation. Hydration levels between 0.05 and 0.62 g/g cysts resulted in a net loss of ATP, whereas above 0.65 g/g cysts a net increase was observed with incubation time. No net change in the amount of ATP, compared with dried cysts, was detected between the latter two hydrations. These results, when integrated with those from previous work, indicate that conventional aerobic energy metabolism does not begin until cyst hydrations of about 0.65 g/g are achieved. The fate of ATP in cysts hydrated to levels lower than 0.65 g/g was discussed.
Studies on the intranuclear distribution of human and mouse genomes and formation of human‐mouse hybrid cells
Authors: Rechsteiner Martin , Parsons Bruce 
Published: February 2005

AbstractAutoradiographic examination of early hybrid cells formed by the fusion of 3H‐thymidine labeled D98/AH2 cells and 3T3‐4E cells revealed that human and mouse chromosomes are often separated within metaphase and interphase nuclei. Although the marked separation of human and mouse chromosomes progressively disappeared with succeeding cell division, the occurrence of sectored nuclei in 16‐cell hybrid colonies and the labeling pattern of human chromosomes within separated metaphases indicate that separation of human and mouse chromosomes may persist through several mitoses.Fusion of 3H‐thymidine labeled D98/AH2 cells and 3T3‐4E cells was coupled with aminopterin selection to study other aspects of hybrid cell formation. Hybrid cells arose from heterokaryons by cell division. Nuclear fusion may have occurred in two out of several thousand heterokaryons examined. However, these could reflect the close apposition of adjacent nuclei. A large fraction (> 0.5) of D98/3T3 heterokaryons underwent at least one cell division. However, the number of hybrid colonies containing more than eight cells at ten days following fusion was about 0.03 of the total number of heterokaryons. Many hybrid colonies arrested growth before the 8‐cell stage, and the cells in such colonies exhibited nuclear abnormalities.
Development of a clonal myogenic cell line with unusual biochemical properties
Authors: Brandt Bruce L. , Kimes Brian W. , Klier F. George 
Published: February 2005

AbstractThe morphological, ultrastructural, biochemical and electro‐physiological properties of B104‐F, a clonal cell line derived from a nitrosoethylurea‐induced neoplasm in a rat, were studied as a function of the growth phase of the culture. Cells in exponentially growing cultures are mononucleate and produce action potentials when stimulated electrically. Stationary phase cultures contain three types of cells: cells of the first type are mononucleate and have long processes containing microfilaments and many parallel microtubules; cells of the second type are mononucleate but contain no microtubules and few microfilaments; and cells of the third type have ultrastructural features typical of multinucleate, striated myotubes. Multinucleate cells generate action potentials with both sodium and calcium components and are depolarized by acetyl‐choline. The acetylcholine response is blocked by d‐tubocurarine. The specific activity of creatine phosphokinase is nine times higher in stationary phase cultures than in exponentially growing ones while the myokinase specific activity is unchanged. The gamma‐aminobutyric acid content of the cells is 3.5‐ to 26‐fold higher in stationary phase than in exponentially growing cultures, depending on the degree of fusion of the culture. The properties of B104‐F are discussed in relation to the properties of developing skeletal muscle and of central nervous system cell lines.
Establishment in culture of a multihormone‐secreting cell strain derived from the mtT/F4 rat pituitary tumor
Authors: Richardson U. Ingrid 
Published: February 2005

AbstractA clonal cell strain F4C1 has been established from the transplantable rat pituitary tumor MtT/F4 and has been maintained in continuous culture for two years. The cells grow with a population doubling time of 48 hours; the karyotype with a modal number of 39 chromosomes includes a pair of large metacentric marker chromosomes. F4C1 cells in culture produce growth hormone and prolactin but not adrenocorticotropin in contrast to the MtT/F4 tumor which secretes all three hormones in the host rat. The cloned cells lack specific receptors for thyrotropin‐releasing hormone and do not respond to this agent with increased prolactin or decreased growth hormone production. Treatment with hydrocortisone results in a small increase in growth hormone and a small decrease in prolactin production. Tumors generated in rats from injected F4C1 cells secrete prolactin and growth hormone but not adrenocorticotropin. The results suggest that growth hormone and prolactin are produced by a single cell type in the MtT/F4 tumor.
Cellular responsiveness to stimulation in vitro: Increased responsiveness to colony stimulating factor of bone marrow colony‐forming cells treated with surface‐active agents and cyclic 3′5′ AMP
Authors: Fleming W. A. , McNeill T. A. 
Published: February 2005

AbstractAddition of low concentrations (10 ng/ml) of saponin or Tween 80 to stimulated cultures of normal mouse bone marrow in agar increased the number of granulocyte‐macrophage colonies which developed. Addition of cyclic AMP or dibutyryl cyclic AMP in low concentration (10−8 to 10−10 M) also enhanced colony numbers although concentrations above 10−5 M were inhibitory. Enhancement was found when marrow cells were pre‐treated with these agents and cultured in their absence.The agents did not stimulate colony development in the absence of colony‐stimulating factor and enhancement of colony number occurred only in cultures containing a concentration of colony‐stimulating factor which was sub‐optimal in terms of maximum colony development.There was no indication of increased colony‐stimulating factor production by treated marrow cells under the experimental conditions used to show colony enhancement. It was concluded that the agents caused an increased responsiveness of colony‐forming cells to colony‐stimulating factor.
Transport and countertransport of thymidine in ATP depleted and thymidine kinase‐deficient novikoff rat hepatoma and mouse L cells: Evidence for a high Km facilitated diffusion system with wide nucleoside specificity
Authors: Plagemann Peter G. W. , Marz Richard , Erbe John 
Published: February 2005

AbstractIncubation of cultured Novikoff rat hepatoma and mouse L cells in a glucose‐free basal medium containing 5 mM KCN and 5 mM iodoacetate for about 10 minutes resulted in a complete depletion of the cells of ATP. ATP‐depleted wild type cells or thymidine kinase‐deficient sublines of Novikoff or L cells took up thymidine rapidly from the medium without concentrating it intracellularly, and exhibited countertransport of thymidine. Thus uptake was by facilitated diffusion. This transport system differs from the substrate‐specific, low‐Km (0.5 μM) thymidine transport system previously described for various types of cultured cells in that it exhibits an at least 100‐fold higher Km and transports equally well various ribo‐ and deoxyribonucleosides. The results suggest that the rate‐limiting step in thymidine incorporation into the nucleotide pool by wild type cells is phosphorylation rather than transport, or that the cells possess two transport systems, a facilitated diffusion system with low substrate specificity and a second system which involves substrate phosphorylation by thymidine kinase.
Density‐dependent changes in the amount of sulfated glycosaminoglycans associated with mouse 3T3 cells
Authors: Underhill C. B. , Keller J. M. 
Published: February 2005

AbstractThe relative amount of sulfated glycosaminoglycans associated with the cell layer of parent and SV40‐transformed Swiss mouse 3T3 cells was determined from the incorporation of labeled sulfate (35SO4) into macromolecular material. In cultures of SV40‐transformed cells, the glycosaminoglycan content per cell was constant over a wide range of densities. In cultures of parent 3T3 cells, the glycosaminoglycan content per cell increased directly with density, the highest values being found in contact‐inhibited cultures. At high cell densities, the glycosaminoglycan content of 3T3 cells was several‐fold higher than that for SV40‐transformed cells. Most of the density‐dependent increase in glycosaminoglycans of 3T3 cells was accounted for by chondroitin sulfate (dermatan sulfate) which was over 6‐fold higher in confluent cultures than in low density cultures.
Ornithine decarboxylase inactivation in HeLa cells
Authors: Prouty W. F. 
Published: February 2005

AbstractOrnithine decarboxylase (ODC) can be induced up to 100‐fold over basal levels four hours after addition of glutamine to the medium of HeLa cells growing in suspension culture. As demonstrated in several other cell types, ODC is inactivated very rapidly in HeLa cells, and the rate of inactivation is seen to vary with a half life of 9–15 minutes in uninduced cells and rises to ca. 60 minutes at the peak of induction. Quantitatively, the change in rate of inactivation cannot completely account for the observed rise in activity, thus synthesis or activation of ODC must also be involved in the induction process. The inactivation process requires metabolic energy and it can be sustained by glycolytic derived energy. Other factors which are known to inhibit protein breakdown in mammalian cells, such as sodium fluoride, insulin, or tosyl phenylalanyl chloromethyl ketone, had no effect on the rate of inactivation of ODC. Attempts to demonstrate ODC inactivation in a cell free system at neutral pH were unsuccessful.
Growth of in vitro colony‐forming cells from normal human peripheral blood leukocytes cultured in diffusion chambers
Authors: Hoelzer D. , Harriss E. B. , Slade M. , Kurrle E. 
Published: February 2005

AbstractThe growth of granulopoietic progenitor cells (CFU‐C) in diffusion chambers during culture of peripheral blood leukocytes from 10 normal subjects has been studied. At various times after initiation of diffusion chamber culture, cells harvested from the chambers were transferred to agar culture for measurement of CFU‐C concentration. Under these conditions colonies could be grown successfully in agar culture provided pronase, necessary for the chamber harvesting procedure, was first removed by careful washing.A marked increase in the number of CFU‐C, up to 25‐fold the initial value, was observed in 8 out of 10 subjects. Here the growth pattern was similar, independent of the initial CFU‐C values, with an immediate rise to a maximum between 6 and 13 days of culture followed by a decrease. In the other two subjects the growth of CFU‐C throughout the diffusion chamber culture period was very poor. The growth of CFU‐C from a given individual's blood was shown to be reproducible in repeated studies in 2 subjects, one of whom showed a proliferative and the other a non‐proliferative pattern.Evidence suggests that the increase in CFU‐C in diffusion chambers is the result of both self‐renewal of these cells and influx from a more primitive compartment, although the present data do not allow an estimate of the relative magnitude of each.
Cell cycle dependent changes in potassium transport
Authors: Mills Barry , Tupper Joseph T. 
Published: February 2005

AbstractK transport has been investigated during progression of cultured Ehrlich ascites tumor cells through the cell cycle. Using a double thymidine block technique, Ehrlich cells carried in continuous culture have been synchronized, as verified by simultaneous monitoring of cell number, cell volume, 3H‐thymidine incorporation and mitotic index. Unidirectional influx, efflux and cell content of K have been monitored throughout the cell cycle. The nature of the pump mediated, ouabain‐sensitive K flux and the furosemide‐sensitive component of K flux, presumably representing K‐K exchange, have also been evaluated. In early S period the ouabain sensitive component, representing the Na‐K pump, comprises 52% of the total unidirectional K influx. During S period the pump activity increases to a maximum of 65% of the unidirectional K influx and subsequently declines during G2 period to a minimum of 40% in mid G2. During M and early S the activity again rises. As the ouabain sensitive component becomes maximal in late S period, the furosemide sensitive component diminishes from approximately 30% of the total influx to approximately 10%. The same pattern is observed in the G2 period. As the pump component diminishes, the furosemide sensitive component increases. Furosemide sensitive K efflux has also been monitored and the pattern is equivalent to that observed in the influx studies. No change in net K flux is observed in the presence of furosemide. This indicates that the furosemide sensitive component represents an exchange component for K. These results are consistent with the conclusion that the alterations in exchange and pump fluxes are physiological events associated with progression of the cell cycle.
Enhanced synthesis and extracellular accumulation of hyaluronic acid during stimulation of quiescent human fibroblasts by mouse epidermal growth factor
Authors: Lembach Kenneth J. 
Published: February 2005

AbstractThe effect of mouse epidermal growth factor (mEGF) on the synthesis of glycosaminoglycans and glycoproteins by human fibroblasts has been studied. The addition of physiological concentrations (10−9 M) of mEGF to quiescent cultures preincubated in the absence of serum was found to elicit an increased incorporation of 3H‐glucosamine into the glycosaminoglycans and glycoproteins of both the cellular and extracellular fractions. Although the growth response to the factor, as measured by DNA replication, was minimal under these conditions as compared with the effect of serum, the mEGF‐induced incorporation of glucosamine into these cellular constituents and into the extracellular glycoproteins was comparable to that elicited by serum shift‐up. Serum, however, caused a significantly larger incorporation of glucoasmine into extracellular, acid‐soluble glycosaminoglycans, which were shown to contain hyaluronic acid as the major component. As previously demonstrated, the growth response to mEGF can be enhanced several fold by an mEGF‐binding arginine esterase, which is normally associated with the factor in vivo, and by ascorbate. The esterase was found to increase markedly the mEGF‐induced incorporation of glucosamine into extracellular hyaluronic acid, while the addition of ascorbic acid did not significantly alter glucosamine incorporation.
Interrelationships between Water and Cellular Metabolism in Artemia cysts. V. 14CO2 incorporation
Authors: Clegg James S. 
Published: February 2005

AbstractThe ability of cysts of the brine shrimp, Artemia salina, to incorporate 14CO2 into organic compounds soluble in cold‐trichloroacetic acid was examined over a broad range of cellular water concentrations. Carbon dioxide was not incorporated by cysts containing less than about 0.3 g H2O/g dried cysts, the “critical hydration” for CO2‐fixation. This relationship held whether the cysts were hydrated from the liquid or the vapor phase. The incorporation of radioactivity was shown to be due exclusively to metabolic activity in the cellular component of the cyst. Above the critical hydration, the amount of 14CO2 incorporated was a function of cyst water content, but the kinds of metabolites labelled with this precursor, and their relative proportions, were found to be similar in cysts of greatly different hydration. Almost all of the radioactivity was associated with amino acids, Krebs cycle intermediates and related acids, and pyrimidine nucleotides. The fact that the pathway involved with CO2‐fixation, and subsequent metabolism of the fixation products are all initiated in cysts containing as little as 0.3 g H2O/g is particularly noteworthy since this hydration level is well within the range of the amounts of “bound water” described in the literature for a wide array of cells and tissues.
Hormonal regulation of amino acid transport and gluconeogenesis in primary cultures of adult rat liver parenchymal cells
Authors: Kletzien Rolf F. , Pariza Michael W. , Becker Joyce E. , Potter Van R. 
Published: February 2005

AbstractAmino acid transport was studied in primary cultures of parenchymal cells isolated from adult rat liver by a collagenase perfusion technique and maintained as a monolayer in a serum‐free culture medium. These cells carried out gluconeogenesis from three carbon precursors (alanine, pyruvate, and lactate) in response to glucagon addition. Amino acid transport was assayed by measuring the uptake of the nonmetabolizable amino acid, α‐aminoisobutyric acid (AIB). Addition of insulin or glucagon to cultured rat liver parenchymal cells resulted in an increased influx of AIB which was reflected in a higher initial rate of AIB transport. The glucocorticoid, dexamethasone, when added alone to cultures did not affect AIB transport. However, prior or simultaneous addition of dexamethasone to glucagon‐treated cells caused a strong potentiation of the glucagon induction of AIB transport. Kinetic analysis of the effects of insulin and glucagon demonstrated that insulin increased the Vmax for transport without changing the Km while glucagon primarily decreased the Km for AIB transport. The effect of dexamethasone was to increase the Vmax of the low Km system.