bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of adenosine 3′,5′‐monophosphate in the transformation of cloudman mouse melanoma cells
Authors: Lincoln Thomas M. , Vaughan Gerald L. 
Published: February 2005

AbstractThe role of adenosine 3′,5′‐monophosphate (cyclic AMP) in the regulation of mouse melanoma cell growth and differentiation was investigated. A variant melanoma (Cloudman S91‐F) which displays a greater degree of transformation than the parental cell (Cloudman S91) was isolated. A correlation between cyclic AMP metabolism and transformation was made. Dibutyryl cyclic AMP depressed cell growth and increased pigmentation in both parental and variant cell lines. The parental cell line, however, was more responsive to melanocyte‐stimulating hormone (MSH) which was found to affect cell growth and pigmentation by increasing cyclic AMP levels. The more transformed S91‐F cell line contained lower levels of cyclic AMP than the parental cell line, and this fact correlated well with the higher degree of growth and lesser degree of pigmentation in the variant. Enzymatic analysis revealed that the hydrolysis of cyclic AMP in both cell lines was similar, while the adenylate cyclase activity of the variant cell line was lower than that of the parental cell line. Lineweaver‐Burk plots demonstrated that the Km′s for the enzymes in the two cell lines were the same but that the Vmax of the S91‐F cell line was significantly less than that of the S91 cell line. Thus, the lesion in the S91‐F cell which is responsible for its more transformed characteristics seems to be one which affects adenylate cyclase at the level of the cell membrane.
Polysomes from cultured muscle cells: The cell‐free synthesis of myosin
Authors: Tepperman Katherine , Essien Francine , Heywood Stuart M. 
Published: February 2005

AbstractThe results reported here have shown that there are significant differences between polysome patterns obtained from cultured cells and from freshly isolated muscle tissue. Polysomes from embryonic homogenates show different patterns with different levels of myosin synthesis, but this does not appear to be the case with cultured cells. Experiments utilizing cell‐free protein synthesizing systems indicate that the polysomes isolated from myoblast cultures can synthesize myosin at levels similar to those obtained from myotube cultures, suggesting that the myoblasts contain significant amounts of the messenger RNA for myosin. In contrast, the polysomes isolated from BrdUrd‐inhibited cultures synthesize a comparatively low level of myosin. These findings illustrate a significant difference between myoblasts and BrdUrd‐inhibited cells.
Transformation of cells by rous sarcoma virus: Cytoplasmic vacuolization
Authors: Bader Artrice V. , Bader John P. 
Published: February 2005

AbstractChick embryo cells transformed by the Bryan “high titer” strain of Rous sarcoma virus (RSV‐BH) are heavily vacuolated. A variety of microscopic techniques have been used in demonstrating that the vacuoles are cytoplasmic, bounded by membrane, and are composed largely of water. Proteins, lipids, glycoproteins, glycolipids, glycosaminoglycans, glycogen, and nucleic acids were undetectable in the vacuoles.Physiological requirements for development of the vacuoles, and reversal of vacuolization, were examined in cells infected with a virus mutant, RSV‐BH‐Ta, which induces reversible temperature‐dependent transformation. Na+ was the only component of the cell culture medium found essential for both the development and reversal of vacuoles. Glucose depletion or dinitrophenol treatment inhibited vacuolization, suggesting a possible energy requirement in the vacuolization process. Ouabain, an inhibitor of Na+−K+ ATPase, enhanced vacuolization, but a variety of other substances affecting cell surface components were inactive. Two sugars, glucosamine and mannosamine, prevented the disappearance of vacuoles.The observations suggest that cellular vacuolization may be a normal physiological response to an increase in water and Na+, and, in the specific case of transformation by RSV‐BH, may be relevant to the physiological basis for malignancy.
Enhancement of phenotypic expression in cultured malignant liver epithelial cells by a complex medium
Authors: Martyn Gunn J. , Shinozuka Hisashi , Williams Gary M. 
Published: February 2005

AbstractThe ability of two media identically supplemented with serum to maintain functional and structural differentiated properties of cultured malignant liver epithelial cells was compared. Reuber H35 hepatoma cells grown in a complex medium, Medium E, possessed the gluconeogenic enzyme phosphoenolpyruvate carboxykinase and bile canaliculi. When grown in Eagle's Minimal Essential Medium, the activity of phosphoenolpyruvate carboxykinase was reduced and bile canaliculi were not formed. This decrease in properties was restored when cells maintained in Minimal Essential Medium were returned to Medium E. It was concluded that the enhanced phenotypic expression was probably due to enrichment of the nutrient environment.
Serum stimulation of Phosphate uptake into 3T3 cells
Authors: Hilborn David A. 
Published: February 2005

AbstractThe stimulation by calf serum of phosphate uptake into 3T3 cells results from a change in maximum velocity of the transport process with no change in the Michaelis constant. Only arsenate among a series of inorganic structural analogs of phosphate inhibited phosphate uptake indicating a high specificity for the process. The arsenate inhibition was competitive in nature. Papaverine, theophylline, and protaglandin E1, drugs known to maintain high intracellular levels of cAMP, had little effect on serum stimulated phosphate uptake. The phosphate uptake stimulating factor(s) in serum could be distinguished from the 3T3 cell survival and migration factors by stability characteristics, but this factor(s) could not be completely separated from a uridine uptake stimulation activity or growth promoting activity using a variety of serum fractionation procedures. Only partial stimulation of the uptake process was achieved with any one serum fraction indicating a multiplicity of serum components is probably involved in this process. Because of the rapidity of serum activation of phosphate uptake and its apparent independence of intracellular cyclic nucleotide levels, it is suggested that serum factors may stimulate phosphate uptake by inducing structural changes in the phosphate carrier system.
Relationship between membrane potential and external potassium in human glioblastoma cells in tissue culture
Authors: Manuelidis Laura , Manuelidis Elias E. , Prichard J. 
Published: February 2005

AbstractCells from a human glioblastoma (TC 526) maintained in tissue culture for ten years had a mean membrane potential of 27 ± 0.9 mV at an external potassium concentration [K0] of 5.3 mM. When [K0] was varied between 2.5 and 5.3 mM, membrane potential changes were close to those predicted by the Nernst equation. At higher [K0], the Nernstian slope was approached only in the presence of 10−5 M ouabain, which did not affect membrane potential at a [K0] of 5.3 mM. An electrogenic sodium pump activated by high [K0] could explain these findings; such a mechanism has been demonstrated in other tissues.
Reversible release of chick embryo fibroblast cultures from density dependent inhibition of growth
Authors: Hovi Tapani , Vaheri Antti 
Published: February 2005

AbstractInitiation of proliferation in density‐inhibited chick embryo fibroblast cultures induced by insulin or trypsin was partially reversed by replacing the medium with supernatants from parallel non‐stimulated cultures. Growth stimulation by neuraminidase, pokeweed mitogen, bacterial lipo polysaccharide or purified tuberculin was less, or not at all, affected by this procedure. Medium change per se caused some proliferation in non‐stimulated cultures.Increased rate of sugar uptake in insulin‐stimulated cultures returned to the level of that in non‐stimulated cultures within a few hours after medium change. This reversion took place apparently irrespective of the phase of the cell cycle. Replacing the medium with supernatants from non‐stimulated cultures induced a rapid decline in subsequent thymidine incorporation during the first S‐phase, and completely abolished the second peak of DNA synthesis. The fraction of cells irreversibly committed to mitosis increased when the time after stimulation increased. Less than three hours' incubation with insulin or trypsin was needed to initiate proliferation of a significant fraction of the cell population. It is concluded that reversion of the initiated cycle of a given cell is no more possible after the cell has entered the S‐phase.
Myonemal contraction of Spirostomum. III. The thermal dependence of contraction, relaxation and excitation‐contraction coupling
Authors: Hawkes R. B. , Holberton D. V. 
Published: February 2005

AbstractA microphotometric technique that displays rapid length changes of Spirostomum has been used to follow the variation with temperature of three kinetic parameters of myonemal contraction: contraction rate, relaxation rate and stimulus duration at threshold. In each case the exponential form of the relationship indicated that the gross rate constant might be equated with the limiting rate constant, k, of a driving chemical reaction, and from standard expressions of chemical kinetics the change in activation free energy appropriate to this reaction has been computed.The thermal dependence of contraction is described by an activation enthalpy (ΔLH‡) of 21.7 kcal mol−1, and the activation entropy (ΔLS‡) of 26.8 e.u. is consistent with a model of contraction requiring neutralization of fixed myonemal charges by divalent cations.The analysis of thermal dependence of relaxation gives a negative activation entropy, a result predicted for a rate‐limiting reaction involving dissociation of a neutral molecule. On the other hand, values of ΔLS‡ and ΔLH‡ for relaxation fall close to an isokinetic correlation drawn in the literature from analysis of the thermal dependence of ciliary beat frequency in different organisms, and for which breakdown of an ATP‐ATPase complex could be the common rate‐limiting reaction.ΔLS‡ for stimulus duration suggests that the rate‐limiting step in excitation‐contraction coupling is a reaction between ions of like charge, or ion pair formation from a neutral molecule.
Effect of exogenous atp on sodium transport in mammalian red cells
Authors: Romualdez A. , Volpi M. , Sha'afi R. I. 
Published: February 2005

AbstractThe effect of exogenous adenosine triphosphate (ATP) and other nucleotides on the transport of Na in various mammalian red cells has been studied. While they have no effect on the transport of Na in human and cat red cells, in dog red cells adenosine and its mono‐, di‐, and triphosphorylated forms were found to increase Na‐influx. Of these, ATP has the most striking effect, causing a more than 8‐fold increase at a concentration of 0.6 mM and exerting this effect at a dose range of 10−5 to 10−3 M. The effect of ATP is rapid (>5 minutes) and can be reversed by washing or the addition of calcium or magnesium. In contrast to the adenosine series other phosphorylated nucleotides (GTP, CTP, UDP, GDP and cAMP) have no effect. The well known volume dependent Na‐transport in these cells is reversed in the presence of 0.6 mM ATP. It is suggested that ATP acts on passive cation movements either by chelation of membrane charge of by a direct interaction with membrane proteins and may be involved in the volume regulation of cation transport in the dog erythrocyte.
The influence of dissolved oxygen on the mitogen responses of mouse lymphocytes
Authors: Kilburn D. G. , Morley M. , Yensen J. 
Published: February 2005

AbstractMouse spleen cells incubated at either 30 mm Hg dissolved oxygen partial pressure (pO2) or 160 mm Hg did not differ significantly in their survival or in their proliferative response to the mitogens concanavalin A, phytohemagglutinin or bacterial endotoxin in a subsequent static culture. If the mitogen was added prior to exposing the cells to the controlled dissolved oxygen environment the incorporation of thymidine was always substantially lower in cells held at 160 mm Hg pO2. This toxic effect of oxygen increased with the time of incubation and was not reversed by the inclusion of 2‐mercaptoethanol in the medium. Incubation of cells with mitogen in the absence of oxygen had no deleterious effect on the proliferative response. A comparison of DNA, RNA and protein synthesis in Con A stimulated cells indicated that the predominant effect of oxygen was on DNA synthesis.
Methionine metabolism in BHK cells: Selection and characterization of ethionine resistant clones
Authors: Caboche Michel 
Published: February 2005

AbstractThe selection of clones resistant to methionine antagonists was undertaken on baby hamster Kidney cells grown in a methionine free medium, supplemented with homocystine, folic acid and hydroxo‐B12. Clones resistant to 30 μg/ml ethionine were isolated after mutagenesis at an induced mutation frequency of 2.3 × 10−5. An ethionine resistant clone, ETH 304, was extensively studied. The resistant cells excreted methionine in the culture medium and the intracellular pools of methionine and SAM were two to five times greater in the resistant clone than in the wild type cells. A semidominant ethionine resistant phenotype was observed in hybrids between the wild type and this resistant clone.Measurement of the specific activity of menadione reductase, B12 methyl‐transferase and ATP: L‐methionine S‐adenosyl‐transferase in crude extracts of the wild type showed a repressive action of methionine on the level of the three enzymes. However, the ethionine resistant clone ETH 304 was not modified in this function. Menadione reductase is feedback‐inhibited by SAM in wild type cells. The enzyme of the ethionine resistant clone was significantly less sensitive to SAM. When a comparison of thermal stability was made between the wild type and ethionine resistant clone enzymes, it was found that the thermal stability of the latter was modified. Three other ethionine resistant clones, independantly isolated, were similarly affected in the properties of menadione reductase.These results suggest that the pathway of re‐use of S‐adenosyl homocysteine, produced during methylation reactions, is highly regulated by methionine and SAM.
A comparative study of superoxide dismutase activity in polymorphonuclear leukocytes, monocytes, and alveolar macrophages of the guinea pig
Authors: Rister Manfred , Baehner Robert L. 
Published: February 2005

AbstractSuperoxide dismutase, an enzyme which catalyzes the dismutation of superoxide radical formed during the univalent reduction of oxygen, was quantitated by observing the inhibition of cytochrome C reduction in three cell fractions in guinea pig peritoneal PMNs and monocytes and compared to alveolar macrophages. No differences were found in the 16,000 × g pellets containing mitochondria, membranes, and granules and representing 96% of total SOD activity in PMNs and monocytes but only 48% total SOD activity in alveolar macrophages. The 100,000 × g microsomal pellet of alveolar macrophages contained 8% of total SOD activity and two‐five times more activity than the respective fractions from monocytes and PMNs. However, there was 70 times more SOD in the 100,000 × g supernatant from alveolar macrophages containing 44% of total enzyme activity than in the same fraction of PMNs and monocytes containing less than 2% total SOD activity. SOD activity is mainly located in the 16,000 × g particulate fraction of PMN and monocytes but more equally distributed between the particulate fractions and cytosol of alveolar macrophages.
Flow microfluorometric analysis of sperm DNA content: Effect of cell shape on the fluorescence distribution
Authors: Gledhill Barton L. , Lake Suzanne , Steinmetz Lloyd L. , Gray Joe W. , Crawford James R. , Dean Phillip N. , Van Dilla Marvin A. 
Published: February 2005

AbstractThe DNA content of individual sperm from populations of acriflavine‐stained cells was investigated by analysis of fluorescence frequency distributions obtained with high‐resolution flow‐systems instruments. Sperm with spherical or cylindrical heads from three mollusk species produce narrow, symmetric fluorescence distributions. Flat sperm heads from six eutherian species produce asymmetric distributions consisting of a peak with a lateral extension to higher fluorescence values. The unexpected shape of these distributions was shown to be due to the flat geometry and high refractive index of the sperm heads in conjunction with the orthogonal axes of flow, excitation, and detection in the flow‐systems instruments. The theoretical and experimental results indicate that the lateral extension can be eliminated either by controlling the sperm orientation with planar flow conditions or by accounting for sperm orientation by means of orientation sensing.
Regulation of cellular growth by sodium pump activity
Authors: Shank Brenda Buckhold , Smith Nancy Egan 
Published: February 2005

AbstractCellular growth has been found to be directly related to the amount of sodium pumping activity in mouse lymphoblasts (L5178‐Y) cultured in varying concentrations of the cardiac glycoside, ouabain. No short‐term adaptation (within one generation) occurred; i.e., neither growth rate nor (Na+ + K+)‐ATPase activity increased in cells cultured for 1–2 days in ouabain.Growth inhibition commenced after two hours, occurring concomitantly with decreased 3H‐leucine incorporation into protein. The time course of this inhibition of protein synthesis, measured by leucine incorporation was similar to, but slightly slower than the time course of the dissipation of the sodium gradient. On the other hand, 3H‐thymidine incorporation is unaffected by ouabain treatment over the same period. The uptake of 3H‐alanine, a neutral amino acid thought to be transported via a Na+‐dependent carrier, was depressed concurrently with the sodium gradient dissipation. It is suggested, therefore, that ouabain inhibition of cellular growth results primarily from the dissipation of the sodium gradient leading to decreased Na+‐dependent transport of amino acids (e.g., alanine) and, therefore, decreased protein synthesis, as observed by leucine incorporation.A sensitive and rapid method for determining ouabain inhibition of cell volume regulation is also described, which may prove potentially useful for assaying Na pump activity.
Pleiotropic phenotype of colchicine‐resistant CHO cells: Cross‐resistance and collateral sensitivity
Authors: Bech‐Hansen N. T. , Till J. E. , Ling V. 
Published: February 2005

AbstractColchicine resistant (CHR) mutants of CHO cells with reduced permeability to colchicine display extensive cross‐resistance to a number of apparently unrelated compounds including puromycin, daunomycin, emetine, ethidium bromide and gramicidin D. A positive correlation was observed between the level of cross‐resistance and the relative hydrophobicity of these compounds. The mutants also showed increased (collateral) sensitivity to local anaesthetics (procaine, tetracaine, xylocaine and propanolol), steroid hormones (1‐dehydrotestosterone, corticosterone and 5β‐pregnan‐3,20‐dione) and some Triton × compounds. In general, the degree of the pleiotropic response (cross‐resistance or collateral sensitivity) correlated with the degree of colchicine resistance in mutant lines. These results are consistent with the pleiotropic phenotype being the result of the same mutation(s) which confer colchicine resistance and support a model for resistance in which the reduced permeability is assumed to be the result of an alteration in the modulation of the fluidity of the surface membrane.
Steroids and hematopoiesis I. The effect of steroids on in vitro erythroid colony growth: Structure/activity relationships
Authors: Singer Jack W. , Samuels Alan I. , Adamson John W. 
Published: February 2005

AbstractWhen substituted steroids of several classes are added to cultures of rat bone marrow cells in the presence of erythropoietin a consistent enhancement of the number of colonies of hemoglobin synthesizing cells is obtained. Maximum steroid effectiveness was found to be between 10−6 and 10−7 M. Representative compounds of several classes of steroids were examined for their ability to enhance colony growth, including δ 4‐estrenes, δ 4‐androstenes, 5α‐H androstanes and estranes, 5β‐H estranes, pregnanes and androstanes. While testosterone and its 5α‐H derivatives had little or no activity, many synthetic derivatives of testosterone were highly active in increasing erythroid colony growth. All 5β‐H androstanes, estranes, and all but one 5β‐H pregnane were active. Cortisol consistently inhibited colony growth and estradiol and progesterone had no significant effect.
Steroids and hematopoiesis II. The effect of steroids on in vitro erythroid colony growth: Evidence for different target cells for different classes of steroids
Authors: Singer Jack W. , Adamson John W. 
Published: February 2005

AbstractAndrogenic steroids and their non‐androgenic 5p‐H metabolites enhance the number of colonies of hemoglobin synthesizing cells grown from rat bone marrow in response to a standard (0.25 unitlml) concentration of erythropoietin. The target cells for two steroids were found to be different. Cells influenced by the androgen, fluoxymesterone (fluoxy), resembled cells responding to erythropoietin in their cycle characteristics, as measured by tritiated thymidine suicide, and in their physical characteristics, as determined by velocity sedimentation gradient separation. Cells responding to etiocholanolone (etio) had a much lower tritiated thymidine suicide rate and different sedimentation velocities. Reincubation of marrow cells with etio for two hours was sufficient to enhance erythroid colony growth by 84%, whereas a similar incubation with fluoxy produced no increment. These studies demonstrate that different classes of steroids may influence in vitro erythropoiesis by acting on distinct populations of marrow cells. Fluoxymesterone appears to act through cells already committed to respond to erythropoietin, while etiocholanolone appears to act on a separate, perhaps more primitive population of marrow cells.
Electrical properties of developing oocytes of the migratory locust, Locusta migratoria
Authors: Wollberg Zvi , Cohen Ephraim , Kalina Moshe 
Published: February 2005

AbstractThe electrical properties of developing nonfertilized oocytes of Locusta migratoria were studied, using intracellular microelectrodes. The inseries potential of the combined oomembrane and of the follicular cells was about 20 mV in the youngest oocytes. It increased as the oocytes developed and it reached a plateau of about 50 mV before full maturation, generally four to seven oocytes away from the fully‐developed terminal oocyte. Current‐voltage relations were always linear for hyperpolarizing currents. Most oocytes exhibited, however, rectification to outward current. Input resistance values varied with oocyte size from about 5 × 106 ohm for young oocytes to about 0.2 × 106 ohm for the more developed ones. Some oocytes displayed a transient depolarization on turning off a hyperpolarizing step of current. This depolarization was not correlated with the size of the oocyte or with any observed morphological feature. Any two adjacent oocytes were electrotonically coupled. A single ovariole thus represented a longitudinal chain of developing oocytes which were connected electrically. This was supported by electron microscope observations which revealed junctions partially impermeable to lanthanum and gap junctions between the follicular cells themselves and between follicular cells and oocytes. The coupling coefficient was dependent on the direction of current flow. The attenuation of voltage along an ovariole was always greater at the distal than at the proximal side.