bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of some ions on the membrane potential of the giant axon of Myxicola
Authors: Goldman L. 
Published: February 2005

AbstractThe effects of various ions on the resting membrane potential of the giant axons of Myxicola were determined. The mean resting potential in artificial sea water is 69 mv, inside negative. The membrane potential decreases with incresing external potassium concentrations, while changes in the sodium and chloride concentrations have little or no effect. For potassium concentrations greater than 50 mM/L the relation between membrane potential and concentration approximates that of a perfectly selective potassium electrode. The data for the whole range of concentrations examined can be well fitted by the equation:

It was pointed out that the Myxicola giant axons can be studied under space voltage clamp and can be made available in the laboratory for 12 months out of the year. Myxicola then should become a very useful preparation for the study of membrane phenomena.
RNA synthesis in synchronously growing populations of HeLa S3 cells. I. Rate of total RNA synthesis and its relationship to DNA synthesis
Authors: Pfeiffer S. E. , Tolmach L. J. 
Published: February 2005

AbstractThe rate of RNA synthesis in synchronously growing HeLa S3 cells was determined as a function of position in the cell generation cycle. Measurements throughout the cycle of both the rate of incorporation of radioactively‐labeled uridine and of the total amount of RNA indicate that (1) the rate of RNA synthesis is constant (or increases only slightly) during G1, approximately doubles during the first half of S, and then remains constant during the remainder of S and G2, and (2) cells attain the average G1 rate of RNA synthesis very early in G1, and maintain the average G2 rate until mitosis.If the initiation of DNA synthesis is blocked, the acceleration of RNA synthesis is markedly reduced or eliminated. Further experiments in which DNA synthesis was inhibited at different times in S, or to varying degrees from the beginning of S, suggest that the extent to which RNA synthesis is accelerated depends on the amount of DNA duplicated. These data also indicate that duplication of the first half, and in particular the first few per cent, of the DNA complement results in a disproportionate acceleration of RNA synthesis.The possibility that fluctuations in the sizes of precursor pools may lead to misinterpretation of labeled‐uridine incorporation data was examined. Experiments indicate that in this system pool fluctuations do not cause invalid measures of RNA synthesis.It is concluded that RNA synthesis occurs throughout interphase, but undergoes a two‐fold increase in rate which is dependent on the duplication of DNA.
Contact regulation of cell division in an epithelial‐like cell line
Authors: Castor Laroy N. 
Published: February 2005

AbstractThe rate of cell division in an epithelial‐like cell line, 1S1, was examined by time‐lapse cinemicrography. When precautions were taken to insure a sufficient nutrient supply, the number of mitoses per unit time in any given area of a confluent monolayer remained constant. This “contact regulation of cell division” resulted in a steadily decreasing frequency of mitosis per cell as the culture became crowded. With the decrease was associated a gradual change in cell shape, from maximally flattened to maximally compact, due to contact inhibition of the movement of cells across one another.When cells were removed along a line scraped on a dense culture, the cells at the edge of the scrape flattened, migrated into the vacant area, and subsequently increased their frequency of mitosis to that characteristic of non‐confluent cells. Inhibition of mitosis caused by a limitation on the nutrient supply was also reversed at a line‐scrape. These observations suggest that cell flattening promoted mitosis by causing the cell membrane to expand, thereby facilitating the uptake of nutrients. The cell membrane would thus function in the mechanism of contact regulation as a transducer, for converting the pressure of the surrounding cell population into a restraining force upon the metabolism of cell division.
Fluctuations of DNA‐dependent RNA polymerase and synthesis of macromolecules during the growth cycle of Novikoff rat hepatoma cells in suspension culture
Authors: Ward Gary A. , Plagemann Peter G. W. 
Published: February 2005

AbstractThe transition of suspension cultures of Novikoff rat hepatoma cells from the exponential to the stationary phase is accompanied by decreases of over 90% in the rates of synthesis of RNA, DNA and protein, a 90% loss of the apparent DNA‐dependent RNA polymerase activity of the cells, and a disaggregation of the polyribosomes with a concomitant accumulation of 80 S and 110 S ribosomal structures. The cells also attain a minimum content of DNA, RNA and protein and a minimum size. Upon dilution of stationary phase cultures with fresh medium, the rate of protein synthesis begins to increase immediately and this correlates with a rapid reformation of the polyribosomes. The initial re‐formation of polyribosomes is little affected by the presence of actinomycin D. RNA polymerase activity also begins to increase immediately after dilution and an increase in rate of RNA synthesis becomes apparent shortly thereafter. The increase in polymerase activity is inhibited by treating the cells with puromycin or actidione. Cell division commences only 9–13 hours after dilution and the rate of DNA synthesis begins to increase about midway through the lag period. During the lag period the average cellular content of protein increases about 80% and that of RNA and DNA about 30%. These increases are accompanied by a marked increase in the average size of the cells.Upon continued incubation of stationary phase cultures, the cells become irreversibly damaged physiologically before gross morphological damage becomes apparent. The irreversible physiological damage is recognized by the fact that the cells fail to recover when suspended in fresh medium.
Genetics of somatic mammalian cells. IX. Quantitation of mutagenesis by physical and chemical agents
Authors: Kao Fa‐Ten , Puck Theodore T. 
Published: February 2005

AbstractThe system previously described for inducing single gene mutations in Chinese hamster cells has been extended to produce additional auxotrophic mutants. An improved method for quantitating the efficiency of single gene mutation to specific auxotrophies has been developed. Mutagenesis in the forward direction has been measured after treatment of these cells with ethyl methanesulfonate, N‐methyl‐N1‐nitro‐N‐nitrosoguanidine, hydroxylamine, an acridine mustard (ICR‐191), caffeine and ultraviolet‐ and X‐irradiation. For each agent, the single cell survival curve and the efficiency of chromatid breakage and rearrangement were measured. Similar measurements were also carried out with a water‐soluble carcinogen N‐nitrosomethylurea, which was shown to be effective in producing auxotrophic, somatic mutations. These results offer promise of illuminating the relationships between cell killing, chromosomal aberration, single gene mutations and carcinogenesis produced by various agents. The methods described can be used in routine testing of drugs, food additives, and environmental pollutants for mutagenic action in mammalian cells in vitro.
Human bone marrow colony growth in agar‐gel
Authors: Pike Beverley L. , Robinson William A. 
Published: February 2005

AbstractA technique for growing human bone marrow cell colonies in agar‐gel medium is described. “Feeder layers” containing 1 × 106 normal human peripheral white blood cells are used as the stimulus for colony growth. Human bone marrow aspirates are collected in heparinized syringes and plated as 2 × 105 cells on “feeder layers.” Normal human bone marrow yields 32–102 colonies per 2 × 105 cells plated. Colonies are almost exclusively granulocytic. Growth rate of colonies is slower than with mouse bone marrow but colonies reach a comparable size (500–1500 cells) at days 12–16.
Inhibition of RNA synthesis by actinomycin D: Characteristic dose‐response of different RNA species
Authors: Perry Robert P. , Kelley Dawn E. 
Published: February 2005

AbstractA quantitative dose‐response study was made of the inhibition by actinomycin D of the synthesis of various RNA species in cultured L cells. After a suitable preincubation with various concentrations of actinomycin, synthesis was measured by a brief incorporation of radioactive uridine. The 45S precursor of ribosomal RNA, 5S ribosomal RNA, transfer RNA and various sized fractions of heterogeneous nuclear RNA were extracted from the appropriate subcellular fractions and resolved by acrylamide gel electrophoresis. Polyribosomal messenger RNA was also studied. Over the range of actinomycin concentrations employed cellular uptake of the drug is proportional to external concentration, and maximal inhibition of RNA synthesis is generally achieved within one hour after exposure.For most of the RNA species studied the dose‐response data appear to follow an exponential inactivation function with some “tailing” evident at the higher doses. Sensitivities, defined as the reciprocal of the dose necessary to reduce synthesis to 1/e of the control level, were compared and examined with respect to the molecular weight of the RNA species under consideration. Among the heterogeneous nuclear RNA's there is a good correlation between RNA size and sensitivity, such that the sensitivity per unit molecular weight is relatively constant. A similar relationship is roughly applicable to the ribosomal and transfer RNA's when taken as a group, although in this case the sensitivity per unit molecular weight is 50 to 100 fold greater.A model is proposed in which this marked difference in actinomycin sensitivity arises as a consequence of the transcription of stretches of contiguous repetitive genes by RNA polymerase molecules which attach to the DNA only at a limited number of entry points, the highest probability of attachment being at the beginning of a stretch.
Mammalian cell fusion. IV. Regulation of chromosome formation from interphase nuclei by various chemical compounds
Authors: Rao Potu N. , Johnson Robert T. 
Published: February 2005

AbstractHybrid HeLa cells formed by the fusion of mitotic with interphase cells have been used as a test system to study the effects of various positively and negatively charged compounds on the induction of premature chromosome condensation (PCC) of the interphase nuclei. Among the various positively charged compounds tested, spermine, putrescine and Mg++ were specific in promoting the PCC induction while spermidine was unique in inhibiting this event. All the negatively charged compounds including estradiol‐17β were uniformly inhibitory. The inhibitory effect of estradiol was reversed by putrescine. The inhibition of PCC induction by estradiol seems to be due to its binding to interphase chromatin rather than to the PCC inducers. The differences between the polyamines in their effects on the PCC inducing system has been explained on the basis of their abilities to bind stereospecifically with chromatin.
Galactose metabolism of mammalian erythrocytes
Authors: Paniker N. V. , Iyer G. Y. N. 
Published: February 2005

AbstractGalactose metabolism in the red cells shows marked interspecies and even intraspecies variations. Red cells of guinea pig, dog and a group of rabbits metabolize galactose to a higher extent than those of other species, including human. In the rabbit, the difference in red cell galactokinase activity could not be correlated to the overall utilization of this sugar in the body.
The roles of calcium and cyclic AMP in the stimulatory action of parathyroid hormone on thymic lymphocyte proliferation
Authors: Whitfield J. F. , MacManus J. P. , Youdale T. , Franks D. J. 
Published: February 2005

AbstractBoth the parathyroid hormone (PTH) and the calcium ion increase the cellular content of cyclic adenosine 3′,5′‐monophosphate (cyclic AMP), promote the initiation of deoxyribonucleic acid synthesis and stimulate the proliferation of rat thymocytes maintained in vitro. The ability of cyclic AMP to serve as the mediator of the mitogenic actions of both PTH and calcium is established by the fact that cyclic AMP itself stimulates cell proliferation in the absence of PTH and extracellular calcium. Neither PTH nor calcium appear to raise the cellular cyclic AMP level by increasing the nucleotide's synthesis by adenylate cyclase (formerly adenyl cyclase); PTH concentrations as high as 50 μg per ml of medium do not increase the enzyme's activity (in the presence or absence of calcium) and mitogenic calcium concentrations inhibit it. PTH also does not directly affect isolated thymocyte phosphodiesterase, but mitogenic calcium levels inhibit the enzyme's activity. Additional experiments show that it is calcium which raises the cyclic AMP level in cells treated with PTH, and some possible calcium‐mediated mechanisms by which the hormone could elevate the cellular cyclic AMP levels are discussed. Thus, the mitogenic action of PTH is primarily mediated by calcium while cyclic AMP is the ultimate implementor of the hormonal action. However, calcium has a dual role and evidence is presented which indicates that besides raising the cellular cyclic AMP level, it also controls the operation of cyclic AMP's mitogenic end‐reaction.
Membrane potentials of BHK (baby hamster kidney) cell line: Ionic and metabolic determinants
Authors: Sachs Howard G. , McDonald Terence F. 
Published: February 2005

AbstractThe transmembrane potential of cells from a continuous cell line (BHK‐21) has been investigated by a combination of electrophysiological and flame photometric techniques. The ratio of sodium permeability to potassium permeability (PNa/PK) determined from membrane potentials recorded at varying external potassium concentrations was 0.082; from membrane potential measurements and the intracellular sodium and potassium concentrations of cells in 6.8 mM K+ media the value was 0.075. The PNa/PK ratio was not temperature dependent. Dinitrophenol (1 mM) did not significantly alter the membrane potential of cells incubated for one hour with the inhibitor. However, iodoacetate (1 mM) and sodium fluoride (30 mM) caused a significant depolarization during a one‐hour incubation. Measurements of sodium and potassium concentrations during incubation at 4°C showed a decrease in internal potassium and an increase in internal sodium accompanied by a decreased membrane potential. Ion concentrations and membrane potentials were measured in cells recovering at 37°C following 24 hours at 4°C. Membrane potentials in excess of EK during the first ten minutes of recovery may indicate electrogenic pumping.
Contact inhibition of speed in 3T3 and its independence from postconfluence inhibition of cell division
Authors: Martz Eric 
Published: February 2005

AbstractThe average speed of nuclear translocation of 3T3 cells, recorded in a time‐lapse film of a perfused culture, was negatively correlated with the number of contacting cells, and, to a lesser degree, with the amount of a cell's perimeter in contact with other cells. When a cell was in contact with five or more other cells, its speed was reduced by 50%, on the average, although the variation in individual cell speed was considerable at each level of contact. A partial correlation analysis showed that any extracellular soluble factors governed by the local cell density had little or no effect on speed, relative to the prominent effect of the number of cell‐cell contacts, and hence that 3T3 cells display true contact inhibition of speed. This confirms the original demonstration by Abercrombie and Heaysman (1952), who studied chick embryo heart fibrpolasts. In our study, the relationships between average speed and age of the culture was such that a possible independent contribution of a time‐associated factor other than contact to the diminution in average speed, although not necessary to account for the data, could not be excluded.The same intercellular contacts found to inhibit speed in this study were previously reported to cause no immediate prolongation of individual cell generation times, despite the fact that the filmed culture was undergoing so‐called “contact” inhibition of cell division. In the present study, moreover, no correlation was observed between the average speeds of individual cells and their generation times. Hence, postconfluence inhibition of cell division and contact inhibition of speed of cell movement seem to be independent phenomena.
The effect of environmental pH on the growth of normal and malignant cells
Authors: Eagle Harry 
Published: February 2005

AbstractData have been presented with respect to the widely varying pH optima for the growth of a number of normal and transformed human, mouse, monkey, hamster, rabbit and rat cell lines. At that optimum, differences between normal and transformed cells with respect to maximum population densities tended to become less prominent. Other differences (serum requirement, long‐term viability of cultures) were not demonstrably pH‐dependent.
Contact inhibition of division: Involvement of the electrical transmembrane potential
Authors: Cone Clarence D. , Tongier Max 
Published: February 2005

AbstractMeasurements of simultaneous mitotic activity, electrical transmembrane potential (Em), and cell density levels in both 3T3 and Chinese hamster ovary (CHO) cell cultures reveal that a 5‐ to 6‐fold increase in the Em level is associated with development of mitotic arrest at saturation densities. This rise occurs both in confluent monolayers and in interior areas of isolated colonies, and is independent of the rate at which confluence is attained. The Em rise is accompanied by a substantial decrease in intracellular Na. Electron microscopy of saturated CHO monolayer sections shows from 46 to 63% of the cell surfaces to be in close apposition (<300 Å spacing). These results for contact inhibited cultures support the hypothesis that mitotic activity may be functionally coupled with the Em level and associated ionic concentration levels. It is suggested that contact inhibition of mitosis may result from a reduction in synthesis of mitogenically essential RNA following a decrease in intracellular Na produced by contact‐induced alteration of surface ion‐transport activity.
The effect of helium and of hydrogen at high pressure on the cell division of Tetrahymena pyriformis W.
Authors: Macdonald A. G. 
Published: February 2005

AbstractThe rate of cell division of Tetrahymena growing in an observational high pressure vessel was measured at selected pressures of helium, hydrogen and at high hydrostatic pressure. Pressures greater than 100 atm reduced the rate of division, but the gases inhibited division to a lesser degree than pure hydrostatic pressure. Hydrogen's effect was distinguishable from that of hydrostatic pressure at 130 atm or more, while helium's effect appeared at 175 atm. These inert gases probably counteract the action of pressure by stabilising apolar pressure‐labile targets.
Dinoflagellate bioluminescence: A comparative study of invitro components
Authors: Schmitter Ruth E. , Njus David , Sulzman Frank M. , Gooch Van D. , Hastings J. W. 
Published: February 2005

AbstractIn vitro bioluminescence components of the dinoflagellates Gonyaulax polyedra, G. tamarensis, Dissodinium lunula, and Pyrocystis noctiluca were studied. The luciferases and luciferins of the four species cross‐react in all combinations. All of these species possess high‐molecular weight luciferases (200,000–400,000 daltons) with similar pH activity profiles. The active single chains of luciferases from the Gonyaulax species have a MW of 130,000 while those from P. noctiluca and D. lunula have a MW of 60,000. Extractable luciferase activity varies with time of day in the two Gonyaulax species, but not in the other two. A luciferin binding protein (LBP) can easily be extracted from the two Gonyaulax species (MW ˜ 120,000 daltons), but none could be detected in extracts of either D. lunula or P. noctiluca. Scintillons are extractable from all four species, but they vary in density and the degree to which activity can be increased by added luciferin. Although the biochemistry of bioluminescence in these dinoflagellates is generally similar, the observations that D. lunula and P. noctiluca apparently lack LBP and have luciferases with low MW single chains require further clarification.
Glucose metabolism of mammalian erythrocytes
Authors: Harvey John W. , Kaneko J. J. 
Published: February 2005

AbstractUnder physiological conditions, erythrocytes of the horse metabolized 638 ± 37 (± SE) nmoles glucose/ml cells/hr at 37°C compared to 942 ± 31 for the cat, 1,329 ± 44 for the dog, and 1,485 ± 43 for man. On an absolute basis, pentose phosphate metabolism was similar between species, with species differences in erythrocyte glucose utilization attributable to differences in Embden‐Meyerhof pathway metabolism. By examining pentose phosphate pathway recycling, it appears that some functional compartmentation exists within erythrocytes.
Magnesium deprivation reproduces the coordinate effects of serum removal or cortisol addition on transport and metabolism in chick embryo fibroblasts
Authors: Rubin H. 
Published: February 2005

AbstractA variety of unrelated effectors stimulate or inhibit coordinately the same array of metabolic reactions in chick embryo fibroblasts, including the uptake of 2‐deoxy‐D‐glucose and uridine, and the incorporation of uridine and thymidine into acid insoluble material. The coordinate inhibition of these reactions by omission of serum or addition of cortisol is reproduced quantitatively by lowering the concentration of magnesium (Mg2+) in medium containing 0.2 mM Ca2+. The response times for the utilization of uridine and thymidine following the removal or addition of Mg2+ are similar to those which follow removal or addition of serum. The effect of serum on the incorporation of choline, which is not part of the coordinate response to unrelated effectors, is not reproduced by varying Mg2+ concentrations. The results support the hypothesis that the availability of Mg2+ within the cell plays a central role in the coordinate control of transport, metabolism and growth by external physiological effectors.
Isolation of UV‐sensitive clones from mouse cell lines by lederberg style replica plating
Authors: Kuroki Toshio , Miyashita Shigeyo Y. 
Published: February 2005

AbstractSeven UV‐sensitive clones were isolated from the mouse cell lines, FM3A and L5178Y, using Lederberg style replica plating. The UV‐sensitive clones were found at a frequency of 1 in 886 clones of FM3A and of 6 in 420 clones of L5178Y, after treatment with N‐methyl‐N′‐nitro‐N‐nitrosoguanidine, but no UV‐sensitive clones were obtained in the untreated controls. The Do values of freshly isolated clones were 10 to 21 ergs/mm2 (mainly 10 to 13 ergs/ mm2), while the original FM3A and L5178Y lines had Do values of 32 ergs/mm2. The UV‐sensitive clones were found to be rather stable for a period ranging from two to eight months after isolation. However, later some of them tended to lose their UV‐sensitivity, in terms of increase in Do values or n values. More stable UV‐sensitive subclones could be isolated from these populations by cloning using the replica plating method. Caffeine was found to potentiate the lethal action of UV‐irradiation on the UV‐sensitive clones as well as on the original FM3A cells.