bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stimulation of growth and calcium influx in cultured, bovine, aortic endothelial cells by platelets and vasoactive substances
Authors: D'amore Patricia , Shepro David 
Published: February 2005

AbstractEndothelial cells (EC) line the heart and blood vessels, and they are the principal cellular components of the microvasculature. The presence of circulating platelets is believed to be necessary to maintain the integrity of the capillary endothelium. Growing EC in culture provides an opportunity to simulate the in vivo situation and to study the response of these cells to platelets and platelet secretions. The addition of platelets at a concentration of 104‐105/mm3 and substances which circulate in blood following injury (serotonin, thrombin, ADP, epinephrine, norepinephrine and histamine) stimulate endothelial proliferation from 150–1,000% of controls. That substances so diverse in form have similar effects suggests a common mode of action, such as mobilization of a second messenger. The influx of 45calcium (45Ca++) in response to these agents was found to be 5 to 24 times that of controls. The stimulation of 45Ca++ influx appears to be dose‐dependent, and it is inhibited by pre‐incubation with lanthanum chloride and specific blocking agents. Calcium as a second messenger is implicated in a variety of cellular functions including division, secretion, motility and enzyme regulation. Thus, the theorized supportive role of platelets on endothelium may be dual and operate, at least at the initial level, by a common mechanism: to mobilize calcium for stimulus‐division following injury and for stimulus‐secretion in normal metabolic activities.
Temperature sensitive mutants of BHK cells affected in cell cycle progression
Authors: Talavera Antonio , Basilico Claudio 
Published: February 2005

AbstractThree different temperature sensitive mutants derived from the Syrian hamster cell line BHK 21 were found to have greatly reduced DNA synthesis at the non‐permissive temperature. These mutants are distinct by complementation analysis and behave at the non‐permissive temperature as cell cycle traverse defective mutants. Microfluorometric analysis of mutant populations arrested at the non‐permissive temperature shows an accumulation of cells with G1 DNA content. Mutants ts 13 and ts HJ4 synchronized in G1 by serum or isoleucine deprivation and shifted to the non‐permissive temperature at the time of release do not enter the S phase, while in the case of mutant ts 11 preincubation at the non‐permissive temperature before release is required to completely prevent its entry into S. Ts 13 and ts 11 are able to traverse the S phase at the non‐permissive temperature when synchronized at the boundary G1/S; in this case, preincubation of ts 11 at the non‐permissive temperature before release does not affect the ability of these cells to perform DNA synthesis. On the other hand, ts HJ4 appears to traverse S only partially when tested under similar conditions. Temperature shift experiments of mutant populations at different times after isoleucine synchronization suggest that ts 13 and ts 11 are blocked at the non‐permissive temperature in early G1, whereas ts HJ4 is probably affected near the initiation of DNA synthesis, or in some early S function.
Responses of protein synthesis and degradation in growth control of WI‐38 cells
Authors: Castor Laroy N. 
Published: February 2005

AbstractThe overall rates of protein synthesis and degradation in perfusion‐grown WI‐38 cells were followed in the three days after a stepdown in the serum concentration of the culture medium, from 10% to 0.3%. Within three hours after the stepdown, the rate of protein synthesis had decreased and the rate of protein degradation had increased, the combined result being the cessation of protein accumulation. The degradation rate returned over the next three days to its original value, but a zero rate of accumulation was retained because the synthesis rate continued to decline. The rate of DNA synthesis remained constant for six hours after the stepdown. It then declined steadily until reaching a minimum about eight hours later. The results show that extracellular control of protein accumulation depends on adjustments in both protein synthesis and protein degradation, and that the adjustments take place rapidly. This behavior suggests that the cell cycle is arrested after a stepdown because post‐mitotic cells are unable to accumulate additional protein. However, an alternative interpretation of the data is that at least part of the changed accumulation is the result, rather than the cause, of the cycle arrest, and that the arrest is caused by other, more specific, reactions than those of general protein metabolism.
Concanavalin A‐binding by cells of the early chick embryo
Authors: Hook S. L. , Sanders E. J. 
Published: February 2005

AbstractThe surfaces of cells from the early embryo of the chick were examined using electron microscope techniques for the visualization of concanavalin A‐binding sites. Horseradish peroxidase and Ferritin labelled concanavalin A were used to determine the distribution of the binding sites. All surfaces of the epiblast and hypoblast layers which were accessible to concanavalin A showed the presence of binding sites in stage 1 embryos. The ventral surface of the epiblast showed a high lectin affinity which may reflect the development of a basal lamina on this surface. The individual hypoblast cells at this stage showed a non‐uniform distribution of binding sites, having a greater affinity on the dorsal surface than the ventral. By the time of primitive streak formation (stage 4–5) the dorsal surface of the epiblast displayed increased binding sites, while the frequency of sites on the ventral surface of the endoblast was reduced. The latter may reflect a change from one cell population to another, which occurs in the lower layer of the embryo at this time. No consistent correlation could be drawn between changes in motility of cells actually invaginating through the primitive streak and changes in affinity for concanavalin A. An overall increase in affinity of the dorsal surface of the epiblast was revealed by Ferritin and may reflect the changes in surface structure occurring in readiness for the morphogenetic migrations of gastrulation.
Reversible inhibition of the hydrocortisone induction of glycerol phosphate dehydrogenase by cytochalasin B in rat glial C6 cells
Authors: Bennett Kimberly , McGinnis James F. , De Vellis Jean 
Published: February 2005

AbstractThe hydrocortisone (HC) induction of glycerol phosphate dehydrogenase (GPDH; EC 1.1.1.8) in rat glial C6 cells was inhibited reversibly and in a dose‐dependent manner by cytochalasin B (CB). CB had no effect on basal level GPDH, total cellular RNA, DNA or protein content nor did it act as a general inhibitor of the rate of protein synthesis. CB did not appear to be acting via dissociation of microtubules since colcemid had no effect on the induction process. The addition of an alternate energy source (sodium pyruvate) did not relieve the CB inhibition of GPDH induction suggesting that CB is not exerting its effect by blocking glucose utilization. The inhibition by CB is not dependent on the temporal sequence of the induction process since it specifically inhibited GPDH induction at any time it was added. CB did not alter the rate of degradation of GPDH in these cells and direct measurements of the specific rate of synthesis of GPDH demonstrated that CB decreased the induced rate of GPDH synthesis by about 60%. The site of inhibition was more precisely defined by experiments which demonstrated a 60% decrease in specific nuclear binding of 3H‐HC even though total cellular uptake of 3H‐HC was unaffected. This effect on nuclear binding of HC is sufficient to account for the decreased accumulation of GPDH activity in CB‐treated cells.
Polyamine metabolism in enucleated mouse L‐cells
Authors: McCormick Frank 
Published: February 2005

AbstractThe distribution of polyamines between the nucleus and the cytoplasm, and the role of the nucleus in polyamine metabolism, have been studied using cells enucleated with cytochalasin B. Spermidine and spermine were found in the nuclear and the cytoplasmic fractions of L929 cells; their concentration was 3‐fold higher in the former fraction. Ornithine decarboxylase activity was only found in the cytoplasm, and this activity could be stimulated in enucleated cells by the addition of fresh medium. These cells synthesized putrescine actively, but the putresoine made was not converted to spermidine, and accumulated to relatively high concentrations. Similarly, methionine did not act as a precursor to spermidine in enucleated cells, in contrast to whole cells, although it was incorporated into cell protein. Spermidine synthesis, unlike putrescine synthesis, appears to be completely dependent on a nuclear component.
Development of action potential in larval muscle fibers in Drosophila melanogaster
Authors: Suzuki Nobuyuki , Kano Masaakira 
Published: February 2005

AbstractIn the presence of tetraethylammonium or barium ions, the larval muscle fibers of Drosophila melanogaster were found to produce an all‐or‐none action potential operated by the calcium channels. The development of this distinctive membrane property during the maturation of muscle cells was studied by measuring the maximum rate of rise of the action potential in the larval muscle fibers at different stages of development from the sixteenth to ninety‐sixth hours after hatching. The value increased significantly with age until a peak was reached at the sixty‐fourth hour, although it became lower again as puparium formation neared at about the ninety‐sixth hour. This suggests that during larval development the muscle fibers develop the ability to generate an action potential due to an inward current through the calcium channels, although the ability became lower at the later stage of larval development.
Dibutyryl cyclic AMP arrests the growth of cultivated cloudman melanoma cells in the late S and G2 phases of the cell cycle
Authors: Dipasquale Albert , McGuire Joseph 
Published: February 2005

AbstractDBcAMP reversibly arrests cultivated Cloudman melanoma cells in the late S and G2 phases of the cell cycle. This is supported by the measurement of DNA synthesis by autoradiography and measurement of cellular DNA by two methods—the diphenylamine reaction and microspectrophotometry of Feulgen stained cells. We also present evidence that (1) cell division is prevented if DBcAMP is added as late in the cycle as early S phase. (2) The inhibition of cell division does not appear to be caused by products of tyrosine oxidation. (3) The increase in cell size that occurs in the presence of DBcAMP reflects continued synthesis of protein in the absence of cell division.
Role of the vacuolar apparatus in augmented protein degradation in cultured fibroblasts
Authors: Amenta J. S. , Sargus M. J. , Venkatesan S. , Shinozuka H. 
Published: February 2005

AbstractRat embryo fibroblasts, grown in Eagle's MEM with 10% serum, showed a rapid increase in autophagic vacuoles when placed in MEM with 0–1% serum. Concurrent with this response, degradation of cellular proteins showed a 2‐fold increase. We did not find any increases in cathepsin D, β‐glucuronidase, β‐galactosidase, and β‐glucosidase, or proteolytic activity of cell homogenates at pH 3.7 towards endogenous substrates. Homogenates prepared in 250 mM sucrose at pH 7.0 showed a 40% increase in protein breakdown. These data support the hypothesis that the induced increase in proteolysis, characteristic of cells placed in a nutritionally deficient medium, is effected by an activated vacuolar apparatus (lysosomes and autophagic vacuoles). We suggest, however, that this mechanism is distinct from normal protein turnover in the cell, but can be rapidly induced by appropriate alterations in the cellular environment. Finally, this induced proteolytic mechanism is not dependent upon an increase in lysosomal enzymes, but rather a structural alteration within the cell which effects a transfer of cellular proteins into the vacuolar apparatus.
Toxicity, radiation sensitivity modification, and metabolic effects of dehydroascorbate and ascorbate in mammalian cells,
Authors: Koch Cameron J. , Biaglow John E. 
Published: February 2005

AbstractDehydroascorbate, an electron affinic metabolite of vitamin C, sensitized Ehrlich ascites tumor cells, in vivo, to radiation and was selectively toxic to V79 Chinese hamster lung cells under hypoxic conditions (without radiation). The radiosensitization may involve both the electron affinic nature of dehydroascorbate as well as its ability to oxidize the intracelluar NAD(P)H and non‐protein sulfhydryl. Dehydroascorbate's oxidation of NAD(P)H required higher concentrations than other sulfhydryl oxidants such as N‐ethylmaleimide and diamide. The oxidation of NAD(P)H by dehydroascorbate could be reversed by glucose. Hypoxic cell radiosensitization of V79 cells in tissue culture by dehydroascorbate could not be easily demonstrated because of the rapid breakdown and appreciable cytotoxicity of the drug at high concentration. The cytotoxicity was found to occur with both high and low densities of V79 cells. With low cell densities small amounts of oxygen did not reduce the cytotoxicity of dehydroascorbate, but virtually eliminated the cytotoxicity of nitroaromatic electron affinic compounds (metronidazole and Ro‐07‐0582). The cytotoxicity to dense cell suspensions was found to depend upon the type of buffer included in the reaction medium. The maximum cytotoxicity was obtained in buffer free saline. The reduced form of dehydroascorbate, vitamin C, was found to be toxic only under aerobic conditions. The aerobic cytotoxicity could be prevented by the addition of catalase to the growth medium or by an increase in cell density, suggesting it was caused entirely by the production of H2O2 from the oxidation of vitamin C.
Increased membrane transport of 2‐deoxyglucose and 3‐0‐methylglucose is an early event in the transformation of chick embryo fibroblasts by rous sarcoma virus
Authors: Lang Dennis R. , Weber Michael J. 
Published: February 2005

AbstractTransformation of chicken embryo fibroblasts with Rous sarcoma virus results in cells with an enhanced rate of hexose uptake. We have examined transport of the glucose analogs 2‐deoxyglucose and 3‐0‐methylglucose in cells infected with a temperature sensitive variant of the virus. In cells shifted from restrictive to permissive conditions for transformation, increased transport of the non‐phosphorylatable analog 3‐0‐methylglucose occurs at the same time as that of 2‐deoxyglucose, a phosphorylatable analog. This enhanced rate of transport can be observed within three hours of the temperature shift. There is a corresponding decrease in the transport rate of both analogs following shift to the restrictive temperature. These results suggest that increased transport is likely to be the primary event in causing transformation‐specific changes in sugar metabolism. We have also examined uptake into the internal pools of both the phosphorylated and non‐phosphorylated forms of 2‐deoxyglucose in normal cells and in cells transformed by the wild‐type virus. These data indicate a corresponding increase in the rate of accumulation of the free sugar in transformed cells and point to transport as the rate limiting step in the accumulation of 2‐deoxyglucose in both normal and transformed chicken embryo cells.
Conditions which affect initiation of animal cell division by trypsin and thrombin
Authors: Carney Darrell H. , Glenn Kevin C. , Cunningham Dennis D. 
Published: February 2005

AbstractIt has been well documented that trypsin or thrombin initiate proliferation of quiescent secondary chick embryo cells. However, there has been less certainty about the ability of these proteases to initiate division of quiescent mammalian cells. Accordingly, we studied the conditions under which quiescent chick embryo (CE), mouse embryo (ME), and human diploid foreskin (HF) cells respond to trypsin or thrombinExtended culture of these cell strains in serum‐free medium increased the initiation of cell division by both proteases. Under these conditions, CE cell number was increased 90% over controls by trypsin and 70% by thrombin. In contrast, quiescent ME and HF cells both responded better to thrombin than trypsin, giving maximal increases, respectively, of 70 and 40% over controls with thrombin and 22 and 14% with trypsin. Calf serum inhibited the initiation of these cell strains, particularly the ME cells, by both trypsin and thrombin. This inhibition of initiation could be attributed to decreased proteolytic activity in the case of trypsin, but not thrombinIn contrast to the cell strains tested, quiescent cultures of the 3T3 cell line showed no detectable increase in cell number with trypsin or thrombin in the absence of serum, and only a slight increase in cell number with thrombin in the presence of serum. However, in the presence of plasma, 3T3 cell number increased up to 20% with thrombinInitiation of cell division by proteases has been reported and confirmed mostly for early passage cell strains rather than cell lines. Our experiments with CE cells indicate that this is possibly the result of a rapid decline in protease responsiveness upon serial subculture. With these cells we found a decline in response first to trypsin, then thrombin, and finally serumThroughout these studies, we compared the ability of trypsin and thrombin to initiate cell division under various conditions. We found several differences between the two proteases, indicating that they initiate cell division by somewhat different mechanisms.
Chloride and sulfate transport in ehrlich ascites tumor cells: Evidence for a common mechanism
Authors: Levinson Charles 
Published: February 2005

AbstractThe effects of phloretin, H2DIDS (4,4′‐diisothiocyano‐1,2‐diphenylethane‐2,2′‐disulfonate) and SO4−2 on anion transport in Ehrlich ascites tumor cells was studied in an effort to determine whether Cl− and SO4−2 share a common transport mechanism. Sulfate, in the presence of constant extracellular Cl− (100 mM), reduces Cl− self‐exchange by 43% (40 mM SO4−2) and Cl−−SO4−2 exchange by 36% (25 mM Cl−/O SO4−2) compared to 25 mM Cl−/50 mM SO4−2. Phloretin blocks without delay and to the same extent the self‐exchange of both Cl− and SO4−2. For example, at 10−4 M phloretin, anion transport is inhibited 28% which increases to 78% at 5 × 10−4 M. Reversibly bound H2DIDS also inhibits the self‐exchange of both Cl− and SO4−2. However, at all H2DIDS concentrations tested (0.5 − 10 × 10−5 M) SO4−2 transport was far more susceptible to inhibition than that of Cl−. H2DIDS when irreversibly bound to the cell inhibits SO4−2 but not Cl− transportThe results of these experiments are consistent with the postulation that both Cl− and SO4−2 are transported by a common mechanism possessing two reactive sites.
Thymidylate synthetase and dihydrofolic acid reductase in the stimulated human lymphocyte
Authors: Haurani Farid I. , Kardinal Carl G. , Biermann William A. 
Published: February 2005

AbstractThe phytohemagglutinin (PHA)‐stimulated human lymphocytes demonstrated trace or no activity of (dihydro) folate acid reductase using three methods including a radioassay, but demonstrated ample activity of thymidylate synthetase. This was true regardless of the day of harvest, (first through seventh) of the stimulated lymphocyte. The lymphocyte extracts revealed no inhibitor to the reductase enzyme when these extracts were added before the liver extracts to the assay system. When methotrexate (MTX) was added to the culture media of the lymphocytes, there was, as expected, an increase in the synthetase activity, but the expected rise in the reductase activity did not occur, it remained nil. On the other hand, MTX did influence the incorporation of nucleosides by the stimulated lymphocytes in a fashion similar to its action on the incorporation of the same nucleosides by other cells.
Heat shock dependent fluctuations of RNase activity during the cell cycle of synchronized Tetrahymena
Authors: Tarnowka M. A. , Yuyama S. 
Published: February 2005

AbstractThe total cellular acid RNase activity per milliliter of culture increases sharply following each heat shock in the cell cycle of Tetrahymena pyriformis ST synchronized with heat shocks spaced one generation time apart. Thus, the RNase activity per 105 cells is 24.5 units immediately after the end of the sixth heat shock, increases to 39.0 units during the following 55 minutes and decreases to 24.2 units at the start of the seventh heat shock. No change in the RNase activity occurs during the heat shock period. In logarithmically growing cells the RNase activity per 105 cells is 15.4 units. The heat shock stimulates the increase in the RNase activity, since no rapid increase occurs during the free running division cycle but a rapid increase occurs after an additional heat shock given at different times during the cell cycleInhibition of the increase in RNase activity by cycloheximide suggests that concurren protein synthesis is required for the stimulation of the RNase activity by the heat shock treatment.
Sodium concentrations affect metabolite uptake and cellular metabolism
Authors: Bader John P. , Sege Robert , Brown Nancy R. 
Published: February 2005

AbstractRates of uptake of glucose (measured with 3H‐2‐deoxy‐d‐glucose), galactose, and leucine increase after exposure of chick embryo cells to increasing concentrations of Na+ over the range 100 to 200 mM. Uptake of nucleosides was unaffected by [Na+] over this range. Prior exposure of cells was required for the [Na+] effect on uptake. Changes were measureable within two hours after changing [Na+], and although the capacity for deoxyglucose uptake remained constant thereafter, the capacity for leucine uptake continued to change during the next few hours. Inhibition of protein synthesis by cycloheximide, or of RNA synthesis by Actinomycin D, failed to prevent these uptake changes. Analysis of the kinetics of uptake showed that only the Km for uptake of deoxyglucose or leucine was affected by [Na+]; the maximum V for each compound remained the same. Effects of [Na+] could be distinguished from the increased capacity for glucose uptake induced by glucose starvation.Incorporation of both radioactive uridine into RNA, and radioactive thymidine into DNA, were affected by [Na+], but the differences were not correlated with uptake of other metabolites. No differences in countable mitoses were apparent, although the growth of chick embryo cells increased slightly with increasing [Na+].Changes in uptake due to differing [Na+] also were observed in mammalian (rat NRK) cells. However, no effects of [Na+] on rates of cell growth or saturation density were observed with these cells.