bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence of a common site of action for the antitumor agents, hydroxyurea and guanazole
Authors: Wright J. A. , Lewis W. H. 
Published: February 2005

AbstractHydroxyurea and guanazole were used as selective agents in tissue culture to obtain independent Chinese hamster ovary cell lines resistant to the cytotoxic effects of hydroxyurea or guanazole. In all cases tested a cell line selected for resistance to one of the antitumor agents exhibited resistance to both drugs. This result supports the view that these two drugs act at a common site.
Effect of PCMBS on water transfer across biological membranes
Authors: Naccache P. , Sha'afi R. I. 
Published: February 2005

AbstractP‐chloromercuriphenylsulfonate, PCMBS, and 5, 5′ dithiobis‐(2‐nitrobenzoic acid), DTNB at a concentration of 1 mM are found to inhibit the rate of water transport across human red cell membrane. In addition PCMBS inhibits the rates of transport of small hydrophilic but not hydrophobic nonelectrolytes. Other sulfhydryl reagents such as N‐ethylmaleimide and iodoacetamide have no significant effect on the rate of water transfer in these cells. The results suggest that there are at least two populations of membrane bound SH‐groups which differ in their topical location which participate in the control of water transfer. One is located closer to the outer surface of the membrane, and thus is readily accessible to PCMBS while the other component is probably located in the membrane interior. These two populations can be dissociated by pH. The effect of PCMBS on water transfer can be greatly influenced by pH and temperature. The main effect of temperature and pH is on the permeability of the membrane to the drug. The same concentration of PCMBS is also found to inhibit to a lesser degree water transfer across other biological membranes.
Erythropoietic progenitors capable of colony formation in culture: Response of normal and genetically anemic W/Wv mice to manipulations of the erythron
Authors: Gregory C. J. , Tepperman A. D. , McCulloch E. A. , Till J. E. 
Published: February 2005

AbstractChanges in the number and erythropoietin sensitivity of erythropoietic progenitor cells (CFU‐E or E) capable of erythropoietin‐dependent colony formation in culture have been measured in mice subjected to a variety of manipulations known to affect erythropoiesis. Injection of erythropoietin into mice whose E levels had been reduced by transfusion‐induced plethora stimulated a striking increase in this population within 24 hours in both spleen and marrow. Following irradiation and marrow transplantation E were found to regenerate in the spleen with a population doubling time of 6 hours. Evidence of erythropoietin‐dependent stimulation of E in vivo under conditions of hemopoietic regeneration was also obtained, although substantial numbers of E were detected in both regenerating spleen and marrow of plethoric mice even without erythropoietin administration, In the same experiments comparable effects of erythropoietin on pluripotent stem cells or the progenitors of granulopoietic colonies in culture were not observed. Detailed studies of the dependence of colony formation on erythropoietin concentration in culture showed variations in erythropoietin sensitivity of E from normal, regenerating and plethoric, erythropoietin‐stim‐ulated spleen and marrow. This finding provides the basis for an extremely fine mechanism regulating the flow of erythropoietic differentiation at the level of the production of E.The number of E present in the marrow of untreated W/WV mice was normal, but their sensitivity to erythropoietin in culture was decreased to a similar extent as E from normal mice exposed to a heightened erythropoietic demand. Plethora had a more marked effect in reducing E numbers in W/WV mice than in +/ + controls and stimulation of E following subsequent erythropoietin administration was highly defective. The results of these studies provide further evidence that cells identified as E represent a stage of differentiation along the erythropoietic pathway that is several steps removed from pluripotent stem cells and support the view that erythropoiesis, granulopoiesis and stem cell self‐renewal are regulated to a major degree by independent mechanisms.
Effect of endotoxin on the production of colony‐stimulating factor by human monocytes and macrophages
Authors: Cline Martin J. , Rothman Belina , Golde David W. 
Published: February 2005

AbstractColony‐stimulating factor (CSF) is necessary for the clonal growth of human bone marrow in vitro. Human blood monocytes and macrophages produce CSF. Endotoxin was found to increase the level of CSF generated by macrophages, but had no stimulatory effect on monocytes. Several other substances known to influence the pinocytic or phagocytic activity of mononuclear phagocytes failed to enhance cellular CSF generation.
Contact inhibition, polyribosomes, and cell surface membranes in cultured mammalian cells
Authors: Levine Elliot M. , Jeng Dai‐Yun , Chang Yvonne 
Published: February 2005

AbstractAn “overlay” method for rapidly and synchronously inducing contact inhibition in normal cultured cells has been developed. Using this method, disaggregation of cytoplasmic polyribosomes has been observed to occur within a matter of hours after overlay, followed by a decrease in cellular ribosomal RNA. Polysome disaggregation was influenced by the extent of cell‐cell interaction and was inhibited by pretreatment of overlay cells with cycloheximide. Treatment of underlay cells with cytosine arabinoside also induced polysome disaggregation, but only after an appreciable lag as compared to that observed in overlaid cultures. Disaggregation could be induced by this method in cultured cells derived from normal tissue but not in cells derived from cancerous tissue. Polysome synthesis in growing “normal” cells (as measured by incorporation of tracer uridine into RNA) was markedly decreased when a cell surface membrane preparation was added to cultures.
Concanavalin A and the initiation of thymic lymphoblast DNA synthesis and proliferation by a calcium‐dependent increase in cyclic GMP level
Authors: Whitfield J. F. , Macmanus J. P. , Boynton A. L. , Gillan D. J. , Isaacs R. J. 
Published: February 2005

AbstractExposure of a thymic lymphocyte population (suspended in serum‐free synthetic medium) to the phytomitogen concanavalin A (Con A) causes brief (within the first 8 to 12 minutes) rises in the cellular contents of cyclic AMP and cyclic GMP. However, the rise in the cyclic GMP level is calcium (extracellular)‐dependent, but the cyclic AMP rise is not. These changes are followed during the next hour by the initiation of DNA synthesis by a large fraction of the lymphoblast subpopulation which, like the preceding cyclic GMP rise, is calcium‐dependent. The stimulated lymphoblasts eventually progress into mitosis. Additional observations indicate that Con A operates by sensitizing lymphoblasts to calcium ions which, in turn, cause the initiation of DNA synthesis by a process mediated by cyclic GMP, but not cyclic AMP.
Agglutination by concanavalin A of normal chick embryo fibroblasts treated by 5‐bromodeoxyuridine (BrdU)
Authors: Biquard Jean‐Michel 
Published: February 2005

AbstractWhen chick embryo fibroblasts are grown for two days in the presence of low doses (18 μg/ml) of 5‐bromodeoxyuridine (BrdU), their agglu‐tinability by Concanavalin A is increased to about the same degree as following viral transformation of the cells by Rous sarcoma virus. Simultaneous addition of a large excess, but not of a low dose of thymidine prevents this effect of BrdU.Treatment with BrdU also enhances the agglutinability of fibroblasts infected with a conditional It mutant of Rcus sarcoma virus at the temperature of 41° which restricts morphological transformation.
Uridine uptake in a unicellular eukaryote during the interdivision period and after growth arrest
Authors: Wolfe Jason 
Published: February 2005

AbstractThe rate of uridine uptake was measured in Tetrahymena after shiftdown to non‐nutrient physiological salt solution. Uptake follows Michaelis‐Menten kinetics and an apparent Km of transport of 2 × 10−6 M has been estimated. This value is in good agreement with those reported for tissue‐derived cells in culture. Incorporation of uridine into RNA follows similar kinetics suggesting that uptake is rate limiting for incorporation. Within three hours after shiftdown the rate of uptake is decreased by an order of magnitude. Also at three hours after shiftdown pairing occurs between cells of complementary mating types. It seems likely that the change in uptake is a reflection of a surface change associated with differentiation. The rate of uptake was also measured during the interdivision period using cells synchronized by a physical selection procedure. A change in rate occurs at the time the cells begin replication of DNA and is essentially stable thereafter. These results indicate that there exists in Tetrahymena a relationship between surface properties as assayed by uridine uptake and properties of growth and differentiation.
Cyclic AMP, membrane transport and cell division. I. Effects of various chemicals on cyclic amp levels and rate of transport of nucleosides, hypoxanthine and deoxyglucose in several lines of cultured cells
Authors: Sheppard J. R. , Plagemann Peter G. W. 
Published: February 2005

AbstractNutrient transport rates and cyclic AMP levels have been implicated in the regulation of cell proliferation. In the present study, however, changes in intracellular cyclic AMP level induced in several lines of cultured cells (normal 3T3 and SV40 and polyomavirus‐transformed 3T3 cells; 3T6, C6 glioma, mouse L, and Novikoff rat hepatoma cells) by treatment with papaverine, prostagladine E, or isoproterenol did not correlate with the inhibition of the uridine, hypoxanthine or deoxyglucose transport rates by these chemicals. Transport inhibitions by above chemicals or Persantin or Cytochalasin B occurred in most cell lines in the absence of any measurable change in intracellular cyclic AMP concentration. Furthermore, treatment of several cell lines with 1 mM dibutyryl cyclic AMP had no immediate effect on the transport of uridine, thymidine or deoxyglucose, although the transport capacity of the cells for uridine and thymidine, but not that for deoxyglucose, decreased progressively with time of treatment. We also observed that the uridine transport system of all cell lines derived from 3T3 cells and the hypoxanthine transport system of L cells exhibited high degrees of resistance to inhibition by the various chemicals. On the other hand, deoxyglucose transport was inhibited to about the same extent by these chemicals in all the cell lines investigated.
Reversible alterations in the mitotic cycle of chick embryo cells in various states of growth regulation
Authors: Rubin H. , Steiner R. 
Published: February 2005

AbstractChick embryo cells which have been kept overnight at pH 6.8 in the absence of serum multiply very slowly. Only a small fraction of cells is in the S period at any given time, and the rate of uptake of 2‐deoxy‐D‐glucose is very low. Upon raising the pH to 7.4 and adding serum (“turn‐on”) the uptake of 2‐deoxy‐D‐glucose increases immediately; the rate of DNA synthesis increases after a lag of about 4 hours, and represents an increase in the fraction of cells synthesizing DNA. The uptake of 2‐deoxy‐D‐glucose is rapidly returned to its original low rate at any time by again lowering the pH and removing serum (“turn‐off”). The synthesis of DNA in the culture remains constant or continues to rise at a markedly reduced rate following the same treatment. Lowering pH or removing serum independently of each other is less efficient at inhibiting the increase in DNA synthesis than the combined treatment but each accomplishes a similar result. Cultures which have been “turnedoff” during the early stages of the rapid increase in DNA synthesis, resume their prior rate of increase immediately if “turned‐on” again within 2.5 hours. If the cultures have been “turned‐off” for 5.5 hours before restoring the “turn‐on,” there is a 2 hour delay before they resume an increased rate of DNA synthesis. The results indicate that chick embryo cells do not become committed to the initiation of DNA synthesis until shortly before, or at the time of the onset of the S period.Up to 96% of the cells in post‐confluent cultures growing in conventional medium become labeled upon continuous, prolonged exposure to 3H‐thymidine. Seventy‐eight percent of the cells in serum‐deprived cultures growing at a very low rate become labeled. These and other considerations suggest that the inhibition of cell multiplication by high population density or serum deprivation is caused by a lengthening of the time cells remain in the prereplicative G1 period rather than by shifting cells into a qualitatively distinct G0 period. There may, however, be a period common to all cells regardless of growth rate, in which cells are not progressing toward the S period. The length of this variable period would then determine the growth rate of a population of cells.
Heterogeneity of in vitro colony‐ and cluster‐forming cells in the mouse marrow: Segregation by velocity sedimentation
Authors: Metcalf D. , Macdonald H. R. 
Published: February 2005

AbstractC57BL bone marrow cells were separated on the basis of their sedimentation velocity at unit gravity and cell fractions cultured in agar using three types of colony stimulating factor (CSF). Colony‐forming cells separated as a single peak (s = 4.4 mm/hr) in cultures stimulated by mouse lung conditioned medium (CSFMLCM) or endotoxin serum (CSFES). Clusterforming cells were separable into two peaks and the majority were larger than colony‐forming cells (s = 5.7 mm/hr). Partial segregation of colony‐forming cells was observed according to the morphological types of colonies generated, large cells tending to generate macrophage colonies and small cells, granulocytic colonies. Large colony‐forming cells were more responsive to stimulation by CSF than small cells. Human urine (CSFHU) appeared unable to stimulate the proliferation of most small colony‐forming cells.Colony‐forming cells appear to be a highly heterogeneous population with intrinsic differences in responsiveness to CSF and with differing capacities to generate colonies whose cells differentiate to granulocytes of macrophages.
Interaction of two mechanisms regulating alkali cations in hela cells
Authors: Cook John S. , Vaughan Gerald L. , Proctor William R. , Brake Emily Tate 
Published: February 2005

AbstractThe alkali cation content of HeLa cells is independent of culture density and of whether the cells are grown in suspension or attached to the culture vessel. With a cell doubling time of 28 hours, the cell K content turns over approximately once per hour. Following partial blockade of the alkali‐cation transport system with ouabain, two distinct but interrelated mechanisms operate in the cellular response: (a) an increase in intracellular Na stimulates the pump so that the short‐term alteration in electrolyte composition is less than would be expected from the fraction of pump sites inhibited, and (b) there is a cyclo‐heximide‐sensitive recovery in transport capacity reflecting a restoration of functional transport sites to their normal density on the cell surface. Experimental manipulations that mimic the effect of ouabain lead to a stimulation of transport, but they do not result in an increase in the number of ouabain‐binding sites on the surface. The data are consistent with a four‐to‐six‐hour turnover of transport sites at the surface, but there is no evidence for a specific induction of the transport system within this short‐term recovery period.
Centrifugal elutriation: Separation of spermatogenic cells on the basis of sedimentation velocity
Authors: Grabske Robert J. , Lake Suzanne , Gledhill Barton L. , Meistrich Marvin L. 
Published: February 2005

AbstractVarious types of cells from the testes of mice and hamsters were separated according to differences in sedimentation velocity by centrifugal elutriation, a counterflow centrifugation technique. Approximately 3 × 108 cells, prepared from six mouse testes or from one hamster testis, were separated into 11 fractions in less than two hours as compared to the 4–5 hours required for sedimentation at unit gravity (“Staput”). Fractions enriched in elongated spermatids and spermatozoa (100%), stages 1–8 spermatids (69%) and pachytene spermatocytes (58%) were obtained from mouse testis dispersions. Similarly enriched fractions were obtained from hamster cells. A single fraction enriched in stages 1–8 spermatids (mouse) was prepared in less than 30 minutes. As many as 2 × 109 cells were separated in a single procedure. Spermatogenic cells exhibited no evidence of structural damage with trypan blue and phase microscopy, and recovery was essentially 100%. Centrifugal elutriation had no effect on sperm motility or on the plating efficiency of CHO cells.
Passive cation movements in the ehrlich ascites tumor cell: The effects of 2,4,6‐trinitrobenzene sulfonic acid
Authors: Smith Thomas C. , Adams Ramona 
Published: February 2005

AbstractWe have investigated the effects of 2,4,6‐trinitrobenzene sulfonic acid (TNBS), an amino reactive reagent, on passive cation movements in Ehrlich ascites tumor cells. Incubation of tumor cells with TNBS (3 mM) results in a two phase association of TNBS with the cells. An initial, rapid phase, presumably at the level of the membrane, is independent of temperature, while the second phase increases linearly in time and is temperature dependent. Kinetic analyses of Na+ movements indicate that TNBS: (1) inhibits Na+ movement from a slowly exchanging cellular compartment, but is without effect on a more rapidly exchanging compartment; (2) does not alter net Na+ accumulation in transport‐inhibited cells; and (3) is without effect on non‐exchange Na+ efflux at 0°C. The actions of TNBS on K+ movements depend upon temperature and the continued presence of TNBS in the environment. At 22°C two minute exposure of the cells to TNBS leads to 77% inhibition of K+ efflux. With continued exposure to TNBS, the inhibition is only 42%. Reduction of the temperature to 0°C decreases K+ efflux in control cells by 82%. Two minute exposure to TNBS enhances K+ efflux by 50%, while continuous exposure increases it by 144%. These results suggest: (1) TNBS interacts with several classes of membrane sites which are involved with the regulation of passive cation movements; and (2) passive Na+ and K+ movements across the cell membrane proceed by different pathways.
Increasing content of poly A(+) mRNA of serum‐stimulated cells in the absence of ribosome synthesis
Authors: Johnson Lee F. , Penman Sheldon , Green Howard 
Published: February 2005

AbstractWhen 3T6 cells undergo a serum‐induced transition from resting to growing state, the number of ribosomes and the amounts of mRNA and tRNA increase as the cells prepare for DNA synthesis. We have examined the effect of preventing ribosome synthesis during this transition. When resting cells are stimulated to grow in the presence of 5‐fluorouridine, mRNA accumulates normally during the first eight hours, though new ribosome formation is completely blocked by the drug. At later times, mRNA continues to accumulate, but at a reduced rate. The ratio of poly A(+) mRNA to rRNA increases from the value characteristic of resting 3T6 (1.8%) to that of growing 3T6 (2.7%) by five hours, and continues to increase to abnormally high values after this time.Although labelling of tRNA is not affected after brief exposure of cells to fluorouridine, the drug prevents the later accumulation of tRNA that ordinarily occurs following serum stimulation of resting cells. This failure of accumulation is not the result of increased lability of fluorinated tRNA, but is probably due to failure of the transcription rate of pre‐tRNA to increase. It is possible that this effect might be due to a regulatory system coupling tRNA content to ribosome content.In cultures stimulated with serum in the presence of fluorouridine the rate of protein synthesis increases with poly A(+) mRNA content during the first eight hours; it then fails to increase further, possibly because ribosomes become rate‐limiting.
The enhanced production of hyaluronic acid by cultured rat fibroblast cells treated with cyclic AMP and its dibutyryl derivative
Authors: Koyama Hideki , Tomida Mikio , Ono Tetsuo 
Published: February 2005

AbstractCells of a newly established rat fibroblast line (SEN) in culture synthesize mucopolysaccharides, which have been identified as hyaluronic acid, chondroitin‐4‐sulfate and heparan sulfate. Treatment of the cells with adenosine 3′:5′‐cyclic monophosphate resulted in a marked stimulation of production of hyaluronic acid, but not of the other mucopolysaccharides. Treated cells also showed increased activity of hyaluronic acid synthetase, a reduction in growth rate, and morphological alteration. In addition, 5‐bromodeoxyuridine was found to counteract greatly the cyclic AMP effect.
Stimulation of melanotic expression in a melanoma cell line by theophylline
Authors: Steinberg Mark L. , Whittaker J. R. 
Published: February 2005

AbstractTheophylline, a phosphodiesterase inhibitor, was found to be a potent stimulator of melanogenesis in the RPMI 3460 hamster melanoma cell line. This stimulation was greater than that caused by either dibutyryl cyclic AMP (db‐cAMP) or another phosphodiesterase inhibitor, papaverine. Theophylline and db‐cAMP treatments also produced strikingly different morphologies in the monolayered cells. The theophylline effect on melanogenesis was diminished by db‐cAMP, whereas simultaneous treatment of cells with db‐cAMP and papaverine produced greater stimulation of melanotic activity than either agent acting alone. Theophylline, therefore, may have phenotypic effects that are at least partially independent of phosphodiesterase inhibition. Theophylline stimulated melanin biosynthesis, as measured by rates of 2‐ [2‐14C] thiouracil incorporation, and also caused an increase in the level of tyrosinase (EC 1.10.3.1) activity. This melanotic stimulation was prevented by the presence of cordycepin or cycloheximide. Theophylline inhibited DNA synthesis and mitosis in the melanoma cell cultures but stimulated protein synthesis. However, inhibition of proliferation and the first appearance of induced melanotic activity did not bear an immediate direct relationship to one another.
Differences in the incorporation of thymidine into DNA of normal and cystic fibrosis fibroblasts in vitro
Authors: Barranco S. C. , Bolton W. E. , Haenelt B. R. , Abell C. W. 
Published: February 2005

AbstractAlthough similar fractions of cells were in the S phase of the cell cycle, normal human skin fibroblasts were shown to incorporate more than twice the 3HTdR into their DNA in vitro than did cells obtained from individuals with cystic fibrosis (CF). Obligate heterozygotes incorporated an intermediate amount of the DNA precursor. Studies were initiated to determine the basis of the differential incorporation of 3HTdR among the genotypes. An analog of thymidine, BUdR, produced varied effects on the growth kinetics of the three genotypes. The growth of cells in BUdR resulted in a 50% increase in the population doubling times of all three genotypes, and caused the cell morphology to change from a spindle shape to one in which the cells became broadened and flat, with numerous cytoplasmic projections extending for distances of several cell diameters. The activities of thymidine kinase and the participation of the exogenous and de novo pathways in the synthesis of TMP were found to be approximately the same in all three genotypes. The data suggest that an alteration in the transport of thymidine into the cells may account for the differences in TdR incorporation into DNA, and this may be associated with other changes in cystic fibrosis that are apparently membrane associated.