bluuebunny/crossref_metadata_2025_split huggingface dataset:
Requirement for calcium ions in lymphocyte transformation stimulated by phytohemagglutinin
Authors: Whitney Richard B. , Sutherland Robert M. 
Published: February 2005

AbstractMedium calcium ions were essential to the development of the lymphocyte transformation response induced by PHA. Magnesium ions could not substitute for calcium ions. Calcium exerted its influence during the induction phase of the process before DNA synthesis began since its removal after the response had fully developed did not alter subsequent levels of nucleic acid synthesis. The early development of RNA synthesis was prevented by low calcium levels indicating that calcium either directly influenced the initiation of this process or some prior event(s).
On the selection for the modal chromosome number in Chinese hamster cells
Authors: Terzi M. 
Published: February 2005

AbstractChinese hamster cell lines have a strong tendency to maintain as modal chromosome number the euploid one characteristic of the species. By following the evolution of karyotypes in cloned subpopulation it has been possible to show that these pseudodiploid constitutions are not simply established due to a selective advantage but they are actually generated in populations where pseudodiploid classes had been absent. The possible role of the mitotic apparatus in keeping and restoring the euploid number is discussed.
The mechanical triggering of bioluminescence in marine dinoflagellates: Chemical basis
Authors: Hamman J. P. , Seliger H. H. 
Published: February 2005

AbstractIn both photosynthetic (Pyrodinium bahamense, Gonyaulax polyedra, Pyrocystis Iunula, P. noctiluca, P. fusiformis) and nonphotosynthetic (Noctiluca miliaris) bioluminescent dinoflagellates chemical stimulation can by‐pass mechanical stimulation. The effective ions are Ca++, K+, NH4+ and H+. Other chemicals found effective are those implicated in Ca++ transport or binding. There are interspecies differences in degrees of mechanical and chemical stimulability. Photoinhibition of mechanical stimulability is the result of two effects, the first a reduction in total bioluminescence potential and the second a decrease in mechanical stimulability resulting experimentally in a decreased rate of light emission. This latter effect can be reversed with Ca++ ions. Chemicals which bind Ca++ or displace Ca++ can mimic the effects of photoinhibition. The chemical inhibition of mechanical stimulability is also reversed by Ca++ ions. A scheme is proposed which is consistent for all species examined.
Selective inhibition of the cell cycle of cultured human diploid fibroblasts by aminonucleoside of puromycin
Authors: Studzinski George P. , Gierthy John F. 
Published: February 2005

AbstractAminonucleoside (AMS) inhibited the cell cycle of human lung fibroblasts at a point in G1 phase and at another point in G2 phase. Even when this inhibition was fully established, DNA synthesis and mitosis which were in progress proceeded normally. Inhibition of RNA synthesis in the cultures preceded the effects on DNA synthesis and mitosis, but inhibition of protein synthesis could not be detected.These points of potential inhibition do not exist in the cell cycle of HeLa cell, or are not affected by aminonucleoside. Here inhibition of cell proliferation by AMS was less marked, and when inhibition eventually occurred it was not specific for any point of the cell cycle. The rate of entry of the inhibitor was similar in both types of cell.
Tetrodotoxin‐resistant electric activity in chick skeletal muscle cells differentiated in vitro
Authors: Kano Masaakira , Shimada Yutaka 
Published: February 2005

AbstractThe embryonic chick skeletal muscle cells differentiated in cell culture from trypsin‐dissociated myoblasts produce a spike response which is tetrodotoxin‐sensitive. It has been found that many cells also produce a plateau response which is resistant to tetrodotoxin. The plateau response frequently occurs even in the muscle cells which do not normally exhibit the spike response. During the plateau response membrane resistance is greatly reduced below its resting value. The current‐voltage relation in muscle cells with the plateau response is always S‐shaped. It is suggested that the plateau arises from a voltage‐dependent increase in permeability to external cations whose influx produce the maintained depolarization, and from low level of repolarizing potassium outflux. The plateau response is sensitive to manganese ions. This finding, together with resistibility to tetrodotoxin, suggests that calcium ions are the dominant carriers for the depolarizing current.
A partially purified polypeptide fraction from rat liver cell conditioned medium with multiplication‐stimulating activity for embryo fibroblasts
Authors: Dulak Norman C. , Temin Howard M. 
Published: February 2005

AbstractA polypeptide fraction with multiplication‐stimulating activity for chicken and rat embryo fibroblasts was partially purified from serum‐free medium conditioned by the growth of a line of rat liver cells. The specific multiplication‐stimulating activity of this fraction was 27,000 times that of serum. The rat liver cell multiplication‐stimulating activity had a molecular weight of approximately 10,000 daltons and was inactivated by mercaptoethanol and dithiothreitol. It had sulfation factor and non‐suppressible insulin‐like activities, but did not have anti‐trypsin activity. The rat liver cell multiplication‐stimulating activity resembled both multiplication‐stimulating activity from calf serum and somatomedin.
Isolation, purification, and chemical characterization of the serum mitogen for diploid human fibroblasts
Authors: Houck J. C. , Cheng R. F. 
Published: February 2005

AbstractWe have found that diploid human fibroblasts, but not heteroploid human fibroblasts, stringently required serum for their multiplication. Using Diaflo ultrafiltration membrane units, isoelectric focusing and preparative gel electrophoresis, we have isolated and purified this mitogenic activity from mammalian sera. This electrophoretically homogeneous sialoprotein is 120,000 daltons in size, with an iso‐electric point of pH 5.2–5.4; it is made up of two electrophoretically identical dimers weighing 57,000 each; it is thermostable and is inactivated by both trypsin and neuraminidase.
Purine excretion by mammalian cells deficient in adenosine kinase
Authors: Chan Teh‐Sheng , Ishii Kazuhiro , Long Cedric , Green Howard 
Published: February 2005

AbstractAn adenosine kinaseless (AK−) mutant of the mouse fibroblast line 3T6 has been obtained in cell culture by evolution of resistance to 6‐thio‐methylpurine ribonucleoside and tubercidin. The mutant excretes purines (xanthine and hypoxanthine) into the culture medium. Human or mouse cells lacking hypoxanthine‐guanine phosphoribosyl transferase (HPT−) excrete increased amounts of purines, but a human cell mutant lacking both HPT and AK excretes considerably more hypoxanthine. The difference in hypoxanthine excretion between the HPT− mutant and the HPT− AK− mutant originates from the adenosine normally reutilized through the activity of adenosine kinase. The activity of adenosine kinase is essential to retard the adenosine cycle and to prevent cellular loss of purines.
Enhancement by purine nucleosides and nucleotides of serum‐induced DNA synthesis in quiescent 3T3 cells
Authors: Schor Seth , Rozengurt Enrique 
Published: February 2005

AbstractPurine nucleotides and nucleosides were found to enhance the DNA synthesis in quiescent 3T3 cells induced either by fresh medium containing calf serum or by the addition of the β‐globulin serum fraction to depleted medium. A two to threefold enhancement has been obtained under these conditions. The adenine and hypoxanthine based compounds were more effective than the guanine ones in the concentration range tested (10−5−−10−3 M), while the pyrimidine compounds were without effect. The degree of enhancement obtained with the purine compounds depended on the type and amount of serum used to stimulate DNA synthesis. A maximal degree of enhancement was obtained when the purine compounds were present for only the first three hours after the addition of serum and thus 18–20 hours before the actual onset of DNA synthesis.
Stimulation of DNA synthesis and 2‐deoxy‐D‐glucose transport in chick embryo cultures by excessive metal concentrations and by a carcinogenic hydrocarbon
Authors: Rubin H. , Koide T. 
Published: February 2005

AbstractChick embryo cultures deprived of serum synthesize DNA at a reduced rate. DNA synthesis in serum‐deprived cultures is stimulated as much as ten‐fold by the addition of Zn++, Mn++ or Cd++ in concentrations just below the toxic level. These metals, in the same concentration range, also stimulate the uptake of 3H‐2‐deoxy‐D‐glucose (2‐DOG). The increase in uptake of 2‐DOG precedes the increase in synthesis of DNA, and is probably an indicator of a more general membrane perturbation. The metals also stimulate DNA synthesis in serum‐containing, density‐inhibited cultures. The carcinogenic hydrocarbon 9,10‐dimethyl‐1,2‐benzanthracene stimulates DNA synthesis and 2‐DOG uptake in serum‐deprived cultures at those concentrations which also cause morphological changes in the culture. Other carcinogenic hydrocarbons, which produce no morphological changes in the culture do not stimulate DNA synthesis. In contrast to these non‐specific effects, DNA synthesis which is inhibited by low concentrations of either ethylene diamine tetraacetate (EDTA) or diethylene triamine pentaacetate (DTPA) is stimulated specifically by Zn++. These findings are interpreted to mean that certain metals and carcinogens, like a variety of other agents, interact non‐specifically with the plasma membrane to initiate a chain of events leading to DNA synthesis, and that one of these events is the liberation of Zn++ for enzyme reactions leading to DNA synthesis.
Electrical properties of normal and dysgenib mouse skeletal muscle in culture
Authors: Powell Jeanne A. , Fambrough Douglas M. 
Published: February 2005

AbstractElectrical properties of normal and dysgenic mouse skeletal muscle were studied by intracellular recording from embryonic cells developing in vitro. Passive membrane constants were determined from records of transmembrane potential responses to hyperpolarizing pulses of current using two types of analyses, assuming the tubes to be finite cylinders: the off transient and steady state analyses. The following properties of normal and dysgenic fibers were also studied. (a) membrane potentials (b) acetylcholine sensitivity (c) α‐Bungarotoxin binding and (d) maximum rate of rise, overshoot and one‐half fall time of the action potential. Rare electrotonic coupling between fibroblasts and myotubes was noted. An anomalous type of rectification Was observed in some fibers in which the transmembrane potential responses possessed under and overshoots. These responses may have affected the values of membrane constants as derived by the off transient analysis. In all parameters studied, including membrane constants derived by the steady state analysis, the cultured mouse cells resembled adult denervated mammalian muscle rather than innervated muscle. There were no differences between normal and dysgenic fibers with respect to any of the parameters studied. Dysgenic fibers did not contract although they displayed passive and active membrane properties like those in normal, non‐dysgenic fibers.
Trichodermin, a possible inhibitor of the termination process of protein synthesis
Authors: Stafford Mary E. , McLaughlin Calvin S. 
Published: February 2005

AbstractThe mode of action of the antibiotic, trichodermin, on yeast cells has been investigated. Trichodermin specifically inhibits protein synthesis and, during the in vivo inhibition of protein synthesis, ribosomes remain in polyribosomes rather than shifting to monoribosomes. This observation suggests that trichodermin inhibits either an elongation step or a termination step of protein biosynthesis. These two possibilities were distinguished by comparing the action of trichodermin with that of cycloheximide, a known elongation inhibitor, upon the reformation of polyribosomes during recovery from a block in polypeptide chain initiation. Cycloheximide slows the recovery of polyribosomes from monoribosomes following a block in polypeptide chain initiation whereas trichodermin enhances the recovery of polyribosomes. This observation is interpreted to mean that trichodermin primarily inhibits the termination step of protein biosynthesis.
Attempted hybridizations with senescent human fibroblasts
Authors: Littlefield John W. 
Published: February 2005

AbstractIf the aging of diploid human fibroblasts reflects stable genetic or epigenetic changes which are few in number and different in different cells, then complementation could occur in hybrids between individual senescent cells. However neither pairs of aged fibroblasts nor even pairs of young and senescent fibroblasts produce viable hybrids under conditions known to promote cell fusion.
Adrenergic antagonists, and a possible link between the increase in cyclic adenosine 3′,5′‐monophosphate and DNA synthesis during liver regeneration
Authors: Macmanus John P. , Braceland Brian M. , Youdale Tony , Whitfield James F. 
Published: February 2005

AbstractThe cyclic‐AMP concentration in the liver remnant after 70% hepatectomy increases in a biphasic manner with peak values at 3 and 12 hours, and DNA synthesis begins at 18 hours. Propranolol (dl) injected at 30 minutes after surgery stopped the first wave of cyclic‐AMP accumulation, but did not affect the second accumulation or the initiation of DNA synthesis. However, dl, propranolol injected at eight hours equally delayed (by 6 to 8 hours) the second wave of cyclic‐AMP accumulation and the initiation of DNA synthesis. Propranolol (dl) did not affect DNA replication per se, since it was totally ineffective after the second wave of cyclic‐AMP accumulation had passed and DNA synthesis had been initiated. Propranolol (dl) action was not due to a blockade of β‐adrenergic receptors, since its d or l isomers were separately without effect, as were unrelated β‐adrenergic blockers (Kü 1313 and M&B 17‐803A).On the other hand, an activation of α‐adrenergic receptors may be involved in the induction of hepatocyte proliferation, since α‐adrenergic antagonists, such as phenoxybenzamine and phentolamine, both delayed and considerably reduced the second wave of cyclic‐AMP accumulation and the subsequent initiation of DNA synthesis. It is concluded that the second wave of cyclic‐AMP accumulation is somehow associated with the initiation of DNA synthesis.
Inhibition of marrow granulocytic colony formation by phytohemagglutinin
Authors: Burns Maria V. , Lozzio Bismarck B. 
Published: February 2005

AbstractThe effect of phytohemagglutinin (PHA) on the growth and number of granulocytic colonies (GC) developing on agar from bone marrow and spleen cells of normal and erythroleukemic mice inoculated with Rauscher leukemogenic virus was studied. Equal number of marrow cells from erythroleukemic mice produced twice as many colonies as those from normal mice. The number of GC developing from either normal and leukemic spleen cells was only 20% to 25% of that arising from marrow cells. The number of cells within each colony was significantly larger in GC formed by myelogenous leukemic cells than those arising from normal cells even though they had similar morphologic features. The addition of 100 μg of PHA per 105 cells reduced the number of GC arising from normal and leukemic cells by 35% and 50%, respectively. Treatment with periodate which mainly inhibits its mitogenic activity, abolished the inhibitory effects of PHA on proliferation of granulocytic cells.
The effect of ploidy on chemical mutagenesis in cultured chinese hamster cells
Authors: Chasin Lawrence A. 
Published: February 2005

AbstractThe frequency of mutations induced by ethyl methane sulfonate was compared in a pseudodiploid Chinese hamster cell strain and in a tetraploid substrain derived from it. The frequency of reverse mutations from glycine auxotrophy to glycine independence was similar in the two strains, as expected for a dominant phenotype. Forward mutation to 6‐thioguanine‐resistance was 25 fold lower in the tetraploid as compared to the diploid strain. The resistant mutants lack hypoxanthine phosphoribosyl transferase activity and their resistant phenotype is recessive in somatic cell hybrids. A combination of chromosomal segregation and mutation could account for the frequency of these recessive drug‐resistant mutants in the tetraploid population.
A kinetic analysis of purine nucleotide synthesis and interconversion in intact Ehrlich ascites tumor cells
Authors: Snyder Floyd F. , Henderson J. Frank 
Published: February 2005

AbstractA pseudo‐first order kinetic analysis has described the reactions of purine ribonucleotide synthesis and interconversion in Ehrlich ascites tumor cells in vitro. Rate constants were determined for 13 reactions at non‐saturating precursor concentration (50 μM); nucleotide formation from adenine‐14C and hypoxanthine‐14C was rate limiting for ATP synthesis and nucleotide formation from guanine‐14C and hypoxanthine‐11C was rate limiting for GTP synthesis. The initial rites of nucleotide synthesis from 1.0 mM adenine‐14C and hypoxanthine‐14C were equivalent to the rates of nucleotide synthesis at non‐saturating base concentration, but the rate of nucleotide synthesis at saturating base concentration after 30 minutes incubation was 20‐25% that of non‐saturating precursor concentration.
The mechanism of regulation of fibroblastic cell replication II. Participation of the nucleoli
Authors: Mironescu Stefan , Ellem K. A. O. , Love R. 
Published: February 2005

AbstractCultures of human diploid fibroblasts (HDFs) exhibiting density dependent inhibition of replication (DDIR) resumed their progression through the cell cycle following medium replacement and, after a lag period of two hours, showed a dramatic increase in the incidence of isonucleolinar 4 cells and in the levels of uptake of 3H‐uridine into the nucleoli. Between five and ten hours after refeeding these nucleolar changes were maximal, leveling off at the highest values, in periods corresponding to late G1 and early S. Concomitantly, a parallel increase in the number of nucleolini per cell occurred. As cells progressed through S and G2 phases the nucleolini decreased in number and reverted to the aniso‐nucleolinar type. The intensity of nucleolar labeling by 3H‐uridine and its correlate, the frequency of cells with labeled nucleoli, also decreased during these cell cycle stages. Both pre‐ and postreplicative periods of mitotic quiescence were characterized by high levels of anisonucleolinosis (60–80% of the cells) and by very low levels of nucleolar 3H‐uridine incorporation.The magnitude of these nucleolar changes occurring during G1 stage was found to be strongly dependent on: (1) the length of time of contact between the cells and the fresh medium, at least eight hours of contact being necessary for a maximal response; (2) the amount of serum in the medium, the optimal serum concentration being between 10 and 50%, and (3) the pH of the medium. The nucleolar response was completely abolished at pH values below 7.0. These nucleolar changes were very sensitive to the presence of cycloheximide (10 μg/ml) and actinomycin D (0.003 μg/ml). The behavior of the nucleoli in response to these parameters was similar to the activation response of the cells to initiate DNA synthesis.During the time period of maximal nucleolar (activation) the onset of DNA synthesis as well as the morphological and autoradiographic manifestations of the nucleolar activation were completely inhibited by very low levels of actinomycin D (Ellem and Mironescu, '72), a selective inhibitor of nucleolar RNA synthesis (Perry, '65). This suggested a possible role of nucleolar metabolism, in normal diploid cells, in the initiation of DNA synthesis. Our results, however, seem to indicate that the nucleolar changes are necessary but not sufficient for the subsequent initiation of DNA synthesis, since with graded serum concentrations or medium volumes, smaller levels of a stimulus were needed to produce maximal isonucleolinosis than to effect a maximum replicative response in the cells.
Studies on Down's syndrome in tissue culture. I. Growth rates protein contents of fibroblast cultures
Authors: Segal David J. , McCoy Ernest E. 
Published: February 2005

AbstractSkin fibroblast cultures from six patients with Down's syndrome (Trisomy 21) were compared with four in vitro age‐matched normal fibroblast cultures. Growth rates were calculated from increases in cell number and total protein during exponential growth, early in culture lifetime (less than 20 doublings). The Down's syndrome (D.S.) cultures had an average population doubling time of 35.6 ± 1.1 hours and average mass doubling time of 38.6 ± 3.2 hours, significantly lower (p<0.005) than the corresponding normal culture values of 23.0 ± 0.7 hours, and 23.3 ± 1.9 hours. D. S. Cells also contained 4.46 ± 0.19 ± 10−4 μg protein/cell as compared to 3.06 ± 0.13 × 10−4 μg/cell (p<0.001) for normal fibroblasts.Similar in vitro observations of increased doubling time and protein content have been reported in normal fibroblasts from older donors, and from individuals with premature aging syndromes, as well as in normal fibroblasts near the end of their in vitro lifetime. The present results, obtained from cultures young in vitro, may therefore suggest that D.S. fibroblast cultures age prematurely. This hypothesis is consistent with clinical manifestations of premature aging in D.S. patients and points to a defect in growth regulation, both in vivo and in vitro, resulting from an extra copy of chromosome 21.
Effect of growth conditions on the activity of ornithine decarboxylase in cultured hepatoma cells. I. Effect of amino acid supply
Authors: Hogan Brigid L. M. , Murden Susan 
Published: February 2005

AbstractOrnithine decarboxylase activity in high density, stationary phase rat hepatoma (HTC) cells in suspension culture has an extremely short half‐life of between 5 and 15 minutes, as measured after inhibiting protein synthesis. Following dilution of these cells into fresh medium there is a large increase in ornithine decarboxylase activity, reaching a peak often several hundred times the initial level at about four hours. At least part of this stimulation is due to an increase in the apparent half‐life of the enzyme, to between 30 and 90 minutes. Evidence is presented that the supply of amino acids can control the turnover of ODC under some conditions. For example supplementing high density cells with glutamine, asparagine, serine, glycine and proline, either singly or together, increases ODC activity and decreases its apparent turnover. The stimulation by amino acids is enhanced by serum.
Peritoneal exudate cells. I. Growth requirement of cells capable of forming colonies in soft agar
Authors: Lin Hsiu‐San , Stewart Carleton C. 
Published: February 2005

AbstractMouse peritoneal exudate cells induced by thioglycollate medium can form colonies in soft agar with a plating efficiency of about 5% (0.6%–10%). Cells from an unstimulated peritoneal cavity form no colonies or have a plating efficiency of less than 0.001 %. These colony‐forming cells from the peritoneal exudate are similar to bone marrow colony‐forming cells in vitro in that they both require a substance(s) present in conditioned medium from L‐cells or mouse embryo fibroblasts or the serum from endotoxin‐treated mice for the initiation and the continuation of their growth. However, peritoneal exudate colony‐forming cells have a much longer initial lag period (10–14 days) and can survive longer in the absence of L‐cell conditioned medium than bone marrow colony‐forming cells. Only mononuclear cells, presumably macrophages, are observed in peritoneal exudate colonies, whereas bone marrow cell colonies contain both polymorphonuclear cells and macrophages.