bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synergistic effects of epidermal growth factor and thrombin on the growth stimulation of diploid chinese hamster fibroblasts
Authors: Cherington Paul V. , Pardee Arthur B. 
Published: February 2005

AbstractThe serum supplement used in the culture of a variety of mammalian cells can be replaced by known growth factors. Diploid Chinese hamster fibroblasts (CHEF/18) will grow for several days in a medium (4F) supplemented with four growth factors: epidermal growth factor (EGF), insulin, fibroblast growth factor (FGF), and transferrin. The growth rate is only about 50% as fast as when fetal calf serum is added. This difference is eliminated by thrombin (10–100 ng/ml; 0.3–3 nM). The CHEF/18 cell line is unique in that no other cell line responds to thrombin in this concentration range.Thrombin acts synergistically with other growth factors to stimulate CHEF/18 cell growth. By itself, thrombin is only mitogenic at elevated concentrations. Thrombin can largely compensate for the absence of EGF and partly for the absence of insulin in serum‐free media. Chemically and “spontaneously” transformed cell lines related to CHEF/18 have lost requirements for both EGF and thrombin, and have retained requirements for insulin and transferrin expressed by CHEF/18. No CHEF cells in this work required FGF. These results suggest that the mechanisms by which EGF and thrombin stimulate cells to grow are related.
Ribonucleotide reduction in intact human diploid fibroblasts
Authors: Dick John E. , Wright Jim A. 
Published: February 2005

AbstractThere have been very few studies on ribonucleotide reductase activity in human tissue. In this report we describe a rapid and convenient procedure for determining purine and pyrimidine ribonucleotide reduction in normal human diploid fibroblasts and use the method to examine some general properties of the activity in these cells. ADP and CDP reductase was characterized for its response to the positive effectors, ATP and dGTP, the negative effector dATP, and the reducing agent dithiothreitol. Apparent Km values for ADP and CDP were determined to be 0.1 mM and 0.04 mM respectively. The antitumor agent hydroxyurea inhibited both purine and pyrimidine reductase in a noncompetitive fashion, giving Ki values of 0.40 mM and 0.41 mM for ADP and CDP respectively. These Ki estimates are about four to five times higher than those reported for some permanent cell lines. An examination of the cytotoxic effects of hydroxyurea indicated a close correlation between the concentration of drug which inhibited enzyme activity and decreased colony‐forming ability.Clearly the ability to investigate ribonucleotide reduction in low numbers of normal human diploid cells will be useful for genetic and biochemical studies.
Osmotic properties of differentiating bone marrow precursor cells: Membrane permeability to non‐electrolytes
Authors: Cicoria A. D. , Hempling H. G. 
Published: February 2005

AbstractMembrane permeability to the non‐electrolyte probes urea and thiourea was measured in a population of differentiating bone marrow precursor cells (Cicoria and Hempling, '80). The phenomenologic equations of Kedem and Katchalsky ('58) were applied. The population of cells, which can be separated by velocity sedimentation, was examined over the maturation range of 400 to 1,000 cubic micra. Several membrane properties were observed: (1) Solute permeability (R̃) increased linearly as the cell volume increased, while the reflection coefficients (σ) remained constant. (2) Membrane permeability to urea was significantly greater than to thiourea; however, their respective sigmas did not differ significantly. Solute permeability was independent of sigma at 22 degrees C. (3) In the two maturation phases observed, wr̃ varied directly with the volume of osmotically active water. (4) The permeability to urea and to thiourea has provided information on the characteristics of the pathways used for water and non‐electrolytes, as well as a description of the phenomenologic membrane events accompanying cellular maturation.
Stimulus secretion coupling: Role of cyclic GMP and calcium in the regulation of secretion from rat exocrine pancreas
Authors: Rochette‐Egly C. , Launay J. F. , Grenier J. F. 
Published: February 2005

AbstractIn rat pancreatic fragments, stimulation of amylase and labeled protein release by carbachol, caerulein, and ionophore A 23187 results within minutes in a short rise in cyclic GMP levels. Cyclic AMP levels do not change significantly. The secretory response elicited by each secretagogue is not modified when combined in pairs. Under intracellular calcium depleting conditions, both the cyclic GMP and the secretory responses to secretagogues are inhibited in parallel, suggesting a good correlation between both processes. Furthermore, 8‐Bromocyclic GMP induces pancreatic secretion, but to a lesser extent, and fails to alter the increase in secretion caused by the various secretagogues. However, other agents such as imidazole, ascorbic acid, phenylhydrazine, and sodium azide also increase cyclic GMP levels but fail to stimulate pancreatic secretion. On the other hand, dibutyryl cyclic AMP also stimulates amylase and labeled protein discharge and potentiates the increase caused by cabachol, caerulein, and ionophore A 23187. These results do not permit conclusions regarding a cause and effect relationship between cyclic GMP and secretion. A role for calcium seems to be the most likely.
Effects of beta adrenergic agents and prostaglandin E1 on erythroid colony (CFU‐E) growth and cyclic AMP formation in friend erythroleukemic cells
Authors: Beckman Barbara , Mirand Edwin , Fisher James W. 
Published: February 2005

AbstractThe formation of erythroid colonies from bone marrow and spleen cells infected with the polycythemic strain of the Friend virus (FV‐P) was characterized in an in vitro methyl cellulose colony‐forming system in response to prostaglandin E1 and the beta‐2 adrenergic agonist, albuterol. Both drugs markedly inhibited the formation of CFU‐E colonies of FV‐P‐infected bone marrow and spleen in the absence or presence of erythropoietin. The albuterolmediated inhibition of CFU‐E colonies (FV‐P‐infected) was selectively blocked by butoxamine, a beta‐2 antagonist. Adenylate cyclase (AC) activity was also determined in FV‐P spleen membrane preparations in response to albuterol and PGE1. Both agents stimulated enzyme activity, and butoxamine blocked the stimulation seen with albuterol. The ability of albuterol and PGE1 to stimulate AC activity in the FV‐P‐infected cells suggests that the effects of these agents on CFU‐E formation may be mediated by specific beta‐2 adrenergic and PG receptors through the adenylate cyclase‐cyclic AMP system.
The use of lanthanum and cytochalasin B to study calcium effects on skeletal muscle differentiation in vitro
Authors: Morris Glenn E. 
Published: February 2005

AbstractA dual effect of external Ca2+ on creatine kinase (CPK) accumulation during myogenesis has recently been demonstrated (Morris and Cole, '79). Ca2+ inhibits muscle‐specific CPK accumulation at intermediate (50–100 μ) concentrations compared with both lower (no added Ca2+) and higher (2–3 μ) concentrations. Myoblast fusion, however, requires high Ca2+ and is inhibited at both low and intermediate Ca2+ levels.These effects are now investigated further by studying the effects of lanthanum ion (La3+), which interferes with Ca2+‐binding to membranes and Ca2+‐transport, and cytochalasin B, which affects the cell membrane and prevents cell fusion without inhibiting CPK accumulation.The results show that low concentrations (10–100 μ) of La3+ inhibit the appearance of the muscle‐specific (MM) CPK isoenzyme during myogenesis without significantly affecting cell fusion or intracellular cyclic AMP levels. Three further observations are consistent with the existence of myotube‐specific membrane‐binding sites for Ca2+, which are involved in the stimulation of CPK accumulation on increasing external Ca2+ from intermediate to high concentrations.(1) CPK levels are not affected by La3+ at 0–50 μ external Ca2+.(2) CPK levels in cytochalasin B treated myoblasts are hardly affected by La3+ at any Ca2+ concentration.(3) In cytochalasin B treated cultures, CPK levels are not increased by raising external Ca2+ from intermediate to high levels.In contrast, the stimulation of CPK accumulation on decreasing external Ca2+ from intermediate to very low concentrations is not affected by either La3+ or cytochalasin B.Some alternative interpretations of the data are also considered, including direct disruption of a membrane Ca2+‐binding site by cytochalasin B.
Hemoglobin biosynthesis in individual bursts from human adult peripheral and umbilical cord blood: Analysis of the relative rates of synthesis of Gγ and Aγ globin chains
Authors: Terasawa Takashi , Ogawa Makio 
Published: February 2005

AbstractWe cultured human adult peripheral and umbilical cord blood mononuclear cells in methylcellulose and measured the synthetic rates of globin chains in individual erythropoietic bursts. Globin chains were labeled with 14C‐amino acids in culture, separated by isoelectric focusing in slab gels containing 8 M urea and 3% Nonidet P‐40, and quantitated by fluorographic methods. All bursts exhibited Gγ, Aγ, and β chains in varying ratios. Cumulative frequency distributions of individual bursts differing in the ratios of Gγ/(Gγ + Aγ) and γ/(γ + γ) approached normal distributions. These results indicated that perinatal hemoglobin switching and the hemoglobin switching of cultured adult erythropoietic precursors do not involve population changes in the precursors. Further, a positive correlation between γ/(γ + γ) and Gγ/(Gγ + Aγ) ratios of individual bursts existed in all of the samples. Switching between γ and β chains and switching of Gγ:Aγ ratios may share common regulatory mechanisms.
Effect of changes in the ionic environment of reticulocytes on the uptake of transferrin‐bound iron
Authors: Paterson Suzanne , Morgan E. H. 
Published: February 2005

AbstractRabbit reticulocytes were incubated with rabbit transferrin labelled with 59Fe and 125I in media in which the NaCl was replaced by other electrolytes or sucrose. Iron and transferrin uptake by the cells was affected by changes in the pH, ionic strength, ionic composition, and the osmolarity of the medium. Uptake was maximal at pH 7.4. A reduction in ionic strength produced by replacing NaCl with sucrose inhibited the uptake in a concentration‐dependant manner, greatest inhibition occurring at lowest salt concentration. Similar results were obtained when KCl, LiCl, RbCl, Na2SO4, or K2SO4 were used instead of NaCl. Low ionic strength was found to inhibit the endocytotic uptake of transferrin labelled with colloidal gold, but had only a small effect on transferrin binding to cell membrane receptors. It was concluded that low ionic strength inhibits iron uptake primarily by blocking the endocytosis of transferrin. Three salts, NH4Cl, CaCl2, and MgCl2, produced different results from the above. NH4Cl inhibited iron uptake at all concentrations used. This action was due to an effect on the release of iron from transferrin, which appeared to be taken up by the cells in a normal manner. When the ionic strength of the sucrose medium was increased by adding low concentrations of CaCl2, iron uptake was greater than with equivalent concentrations of NaCl. However, with CaCl2 concentrations above 10 mM, iron uptake was inhibited, due to inhibition of transferrin uptake, possibly by blocking endocytosis. By contrast, MgCl2 stimulated iron uptake at all concentrations used. The results are discussed in terms of the possible effects of ionic strength, pH, and ionic composition of the extracellular fluid on the three main steps involved in iron uptake by immature erythroid cells: transferrin‐receptor interaction, endocytosis, and iron release from transferrin.
Na+, K+‐ATPase in HeLa cells after prolonged growth in low K+ or ouabain
Authors: Pollack Lewis R. , Tate Emily H. , Cook John S. 
Published: February 2005

AbstractEffects of long‐term, subtotal inhibition of Na+‐K+ transport, either by growth of cells in sublethal concentrations of ouabain or in low‐K+ medium, are described for HeLa cells. After prolonged growth in 2 × 10−8 M ouabain, the total number of ouabain molecules bound per cell increases by as much as a factor of three, mostly due to internalization of the drug. There is only about a 20% increase in ouabain‐binding sites on the plasma membrane, representing amodest induction of Na+, K+‐ATPase.In contrast, after long‐term growth in low K+ there can be a twofold or greater increase in ouabain binding per cell, and in this case the additional sites are located in the plasma membrane. The increase is reversible. To assess the corresponding transport changes, we have separately estimated the contributions of increased intracellular [Na+] and of transport capacity (number of transport sites) to transport regulation. During both induction and reversal, short‐term regulation is achieved primarily by changes in [Na+]i. More slowly, long‐term regulation is achieved by changes in the number of functional transporters in the plasma membrane as assessed by ouabain binding, Vmax for transport, and specific phosphorylation.Parallel exposure of cryptic Na+, K+‐ATPase activity with sodium dodecyl sulfate in the plasma membranes of both induced and control cells showed that the induction cannot be accounted for by an exposure of preexisting Na+, K+‐ATPase in the plasma membrane. Analysis of the kinetics of reversal indicates that it may be due to a post‐translational event.
The use of fluorescent antimyosin and DNA labeling for the estimation of the myoblast and myocyte population of primary rat heart cell cultures
Authors: Masse Marie J. O. , Harary Isaac 
Published: February 2005

AbstractCell division in heart muscle cells progressively ceases during the development of the rat heart, leading to an adult stage with muscle cells incapable of cell division. We have quantitatively determined the number of dividing and nondividing heart muscle cells in cultures derived from different stages of the developing rat heart with the use of 3HTdR continuous labeling and fluorescent antimyosin staining. The cultures were derived from 14 and 17 day postcoital (dPC) rat embryos and from 1 and 4 day postnatal (dPN) rats. The percent nondividing cells increased with development and the age of the postnatal rat. The percent nondividing cells in 14 dPC equalled 21%, 17 dPC equalled 25%, 1 dPN equalled 44%, and 4 dPN equalled 60%. This method for the quantitative determination of dividing and nondividing cells in the developing rat heart provides a model that is useful for the study of the mechanism of the loss of cell division capacity.
Oxygen enhances fusion of cultured chick embryo myoblasts
Authors: Hollenberg Milton , Honbo Norman , Ghani Q. Perveen , Samorodin Albert J. 
Published: February 2005

AbstractFusion of mononucleate myoblasts to form multinucleated myotubes increases when skeletal muscle cells are grown in progressively higher oxygen concentrations (5%, 20%, and 40% oxygen). At four days of growth fusion of myoblasts (as expressed by the percent of all muscle nuclei that are located in myotubes) is 57 ± 2% in 5% oxygen, 68 ± 1% in 20% oxygen, and 78 ± 2% in 40% oxygen (P<0.001). However, at a concentration of 40%, oxygen depresses the rate of cell division and thereby affects the number of myoblasts available for fusion. Thus, oxygen concentration significantly modifies growth of skeletal muscle in vitro. Its net effect on myotube formation results from the interaction of its separate effects to enhance cell fusion and to depress cell proliferation.
The effect of sarcomere non‐uniformity on the sarcomere length‐tension relationship of skinned fibers
Authors: Iwazumi Tatsuo , Pollack Gerald H. 
Published: February 2005

AbstractIt has proved difficult to activate skinned muscle fibers to produce high tension (3 kg/cm2 level) without loss of clear striations. A new method was developed which permits high tension production in skinned muscle fibers while retaining clear striations. Clear striations allow reliable measurement of the sarcomere lengths during contraction by microscopy and diffractometry. The method is to increase the Ca++ concentration of the bathing solution very gradually over a time period of 5 to 10 minutes. Once the skinned fiber is conditioned by this slow activation, subsequent contractions can be elicited by ordinary quick activations without loss of striations. When the experiments are carried out with careful controls for the uniformity of the sarcomere length distribution along the entire length of the fiber, contractions are highly repeatable. Using the new method and stringent quality control of fibers, the sarcomere length‐isometric tension relationship of skinned rabbit soleus fibers was obtained. The results differ from those previously obtained by conventional activation methods in that tension increases with sarcomere length not only at low (pCa = 5.8), but also at high (pCa = 5.2), calcium concentration.
Variable coupling of active NA+ + K+ transport in Ehrlich ascites tumor cells: Regulation by external NA+ and K+
Authors: Smith Thomas C. , Robinson Susan C. 
Published: February 2005

AbstractThe effects of altered external sodium and potassium concentrations on steady state, active Na+ + K+ transport in Ehrlich ascites tumor cells have been investigated. Membrane permeability to Na+ and K+, intracellular [Na+] and [K+], and membrane potential were measured. Active cation fluxes were calculated as equal and membrane potential were measured. Active cation fluxes were calculated as equal and opposite to the net, diffusional leak fluxes. Elevation of external K+ (6–60 Mm)by equivalent replacement of Na+ (154–91 mM) inhibits both active Na+ and K+ fluxes, but not proportionally. This results in a decrease of the coupling ratio (rp = ‐Jkp/J) as external K+ is increased. Elevation of external K+ (3–68 mM) at constant Na+ (92mM) inbibits J, but is without effect on J. The coupling ratio declines from 1.01 ± 0.14 to 0.07 ± 0.05, a 14‐fold alteration. Reduction of external Na+ (154–25 mM) at constant K+ (6mM) depresses J, but is without effect on J. The coupling ratio increases from 0.63 ± 0.04 at 154 mM Na+ to 4.5 ± 2.04 at 25 mM Na+. The results of this investigation are consistent with the independent regulation of active cation fluxes by the transported species. Kinetic analysis of the data indicates that elevation of external sodium stimulates active sodium efflux by interacting at “modifier sites” at the outer cell surface. Similarly, external potassium inhibits active potassium influx by interaction at separate modifier sites.
Cation transport and growth regulation in neuroblastoma cells. Modulations of K+ transport and electrical membrane properties during the cell cycle
Authors: Boonstra Johannes , Mummery Christine L. , Tertoolen Leon G.J. , Van Der Saag Paul T. , De Laat Siegfried W. 
Published: February 2005

AbstractCation transport and membrane potential were studied during the cell cycle of neuroblastoma cells (clone Neuro‐2A) to investigate the role of these parameters in growth regulation. The cells were synchronized by selective detachment of mitotic cells. The membrane potential and intracellular K+ activity were measured with conventional and K+‐selective microelectrodes respectively. Both the membrane potential and K+ activity were high in mitosis, decreased to half maximal in G1 phase, and rose again during S phase.K+ efflux across the plasma membrane was studied with 42K+ as a radioactive tracer using a washing method for cells grown in monolayer and a continuous efflux method for mitotic cells in suspension. The intracellular K+ content and unidirectional K+ efflux rate obtained from these measurements showed modulations during the cell cycle similar to those of the membrane potential. Using equations of electrodiffusion theory the membrane permeabilities to K+ and Na+ were calculated. These permeabilities were high in mitosis, decreased rapidly in G1 phase and increased during S phase, followed by a transient decrease in G2 phase. A rapid increase was observed between G2 phase and the next mitosis. A similar pattern was obtained for the K+ conductance. K+ resistance changes during the cell cycle were similar to changes in the specific membrane resistance, measured by microelectrodes, except for the early cell cycle phases (mitosis and G1).These studies clearly demonstrate large modulations of the passive membrane permeability properties during the cell cycle. These modulations can be correlated with physicochemical membrane variations during the cell cycle, such as membrane fluidity and lateral mobility of lipids.
Replication pattern of a large homogenously staining chromosome region in antifolate‐resistant Chinese hamster cell lines
Authors: Hamlin Joyce L. , Biedler June L. 
Published: February 2005

AbstractWe have investigated the replication pattern of a large, homogenously staining chromosome region (HSR) in two antifolate‐resistant Chinese hamster cell lines. This region is believed to be the location of an amplified genetic sequence which includes at least the gene coding for dihydrofolate reductase and which may be present in as many as 200 copies. It is shown that the HSR in both cell lines is among the first chromosome regions to begin DNA synthesis after reversal of an early G1 block. In cells synchronized in the S period with hydroxyurea, it is also clear that the HSR in both cell lines begins replication at many sites within its length in early S. The replicons comprising the HSR therefore may respond to a common initiation signal in early S. In one cell line (A3), replication of the HSR requires, at most, 3 hours of a 7‐hour S period; in a second line (MQ19), replication proceeds for approximately 5 hours. In neither line does replication of the HSR occur concomitantly with synthesis of characteristic late replicating regions. These results were confirmed in exponential cultures using a retroactive labeling technique.The significance of these findings is discussed with reference to the possible origin and arrangement of the amplified sequence in these two cell lines.
Nuclear magnetic resonance study of muscle water protons in muscular dystrophy of chickens
Authors: Chang D. C. , Misra L. K. , Beall P. T. , Fanguy R. C. , Hazlewood C. F. 
Published: February 2005

AbstractUsing the pulsed nuclear magnetic resonance (NMR) spectroscopy, the spin‐lattice (T1) and the spin‐spin (T2) relaxations times of water protons from samples of pectoralis major muscles of normal (line 412) and homozygous dystrophic (line 413) chickens were measured. Both the T1 and T2 were significantly increased (P < 0.05) in the dystrophic muscles. The mean values of the relaxation times are given ± S.D. The T1 values were 654 ± 22 msec in normal and 692 ± 41 msec in dystrophic muscles. The T2 values for normal and dystrophic muscles were 39 ± 4 msec and 52 ± 7 msec, respectively. Although the water content of dystrophic muscles (78.9 ± 0.6%) determined by gravimetric methods was significantly higher than normal muscles (74.9 ± 1.1%), this difference in tissue hydration could not explain quantitatively the increase of T1 and T2 values in the dystrophic muscles. The results of the measurements of the relaxation times seem to suggest that there are changes in the composition and/or conformational state of the proteins.