bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density gradient centrifugation of hemopoietic colony‐forming cells
Authors: Turner R. W. A. , Siminovitch L. , McCulloch E. A. , Till J. E. 
Published: February 2005

AbstractBuoyant density distributions of hemopoietic colony‐forming units (CFU) from normal mouse marrow were determined by equilibrium density gradient centrifugation in bovine serum albumin (BSA) gradients. The distributions were compared with those obtained for the total population of nucleated cells from normal mouse marrow. The buoyant density distribution for CFU was found to differ from the density distribution for the total nucleated cell population, and the portion of the total cell population with densities much less than the mean value was found to contain up to a 30‐fold greater proportion of CFU than an uncentrifuged control. These results provide a preliminary approach to the purification and characterization of normal hemopoietic colony‐forming stem cells.
Tissue compatibility in regenerating explants from the colonial marine hydroid Hydractinia echinata (Flem.)
Authors: Toth Steven E. 
Published: February 2005

AbstractArtificially maintained colonies of the colonial marine hydroid Hydractinia echinata are endogenously limited in lateral growth and usually develop in a circular pattern with a closed periderm. Further lateral growth consists of free stolons. Preliminary studies of tissue compatibility in regenerating explants indicate that fusion generally fails to occur if the opposing explants are of differing sex, from different individuals of the same sex, or if peripheral explant contact occurs after free stolons have begun to form. Of the three aforementioned causes of fusion failure, the most important factor appears to be the timing of peripheral explant contact. If regenerating explants contact each other before the endogenous circular growth pattern is achieved, fusion will occur regardless of sex and/or individuality. Incompatibility between explants from the same individual may be because of periderm development inhibition in some instances. However, the failure of free stolon fusion between explants from the same individual suggests the development of “temporal specificity” once the endogenous limit of lateral growth is achieved.
Characteristics of an adenosine triphosphatase in erythrocyte membranes stimulated by 2,4‐dinitrophenol
Authors: Laris Philip C. , Letchworth Peter E. 
Published: February 2005

AbstractStudies were made of the stimulation by 2,4‐dinitrophenol (DNP) of an adenosine triphosphatase (ATPase) in stromata of human erythrocytes. Activation by 2,4‐dinitrophenol occurs in the range 10−5 to 10−3 M and was seen in whole cells, ghosts reconstituted with Mg and ATP, and in osmotic ghosts prepared at a low ratio of cells to water. Phloretin and phloridzin also activated the DNP sensitive system but inhibited it at higher concentrations. DNP increased the Km and Vmax values of the enzyme equally. The DNP sensitive and Na+ + K+ sensitive enzymes of the stromata were compared. The activities of the two ATPases are additive, require the presence of Mg++ and require that the substrate be located at the inner surface of the membrane. The two enzymes differ in their substrate specificity, in their sensitivity to inhibition by ouabain and phloretin and in their sensitivity to some factor in hemolysates. The possible roles of this system in the erythrocyte were discussed.
Observations on acid phosphatase in Mayorella palestinensis
Authors: Lasman M. 
Published: February 2005

AbstractAcid phosphatase activity has been studied in the ameba Mayorella palestinensis. Optimum activity of the enzyme was found to be at a pH of 3.2. The enzyme is inhibited by fluoride ion, but is not sensitive to Mg++.The activity was found to be correlated with age of culture. Two maxima have been obtained, one from cultures in the logarithmic phase, and the other during the period of maximal cell encystation. These results suggest that acid phosphatase play an important role in cell metabolism during growth and differentiation processes of this ameba.
Repolarization of striated muscle fibers by the antifatigue agent, K‐Mg‐aspartate
Authors: Henderson Edward G. , Walkenstein Sidney S. 
Published: February 2005

AbstractResting membrane potentials of isolated frog sartorius muscles were measured under a variety of conditions using intracellular glass microelectrodes. Muscle cells depolarized by the addition of 5.0 or 10.0 mM KCl to the bathing Ringer solution can be repolarized some 5 to 10 mV by the substitution of an equivalent amount of K‐aspartate for KCl in the presence of 2.0 mM Mg++. The repolarization produced by this method persists when the muscle is again placed in the initial KCl solution, thus eliminating the possibility that the hyperpolarization is due to the reduction of chloride in the bathing medium. If for some reason the resting membrane potential of the muscle fibers is considerably below (less negative than) the normal level of 92 mV reported for muscles bathed in 2.5 mM Ringer solution, the substitution of 2.5 mM K‐aspartate for the 2.5 mM KCl and the addition of 2.0 mM Mg‐aspartate to the Ringer solution will, within 15 minutes, repolarize the fiber to the normal level. Magnesium ions alone will not produce the observed repolarization nor can it be attributed to a reduction in the activity of the potassium in the Ringer solution.
Oxygen consumption in diapausing blastocysts
Authors: Gulyas Bela J. , Daniel Joseph C. 
Published: February 2005

AbstractThe oxygen consumption of various diapausing blastocysts from mammals having delayed implantation (mink, northern fur seal, black bear, armadillo and lactating rat) was studied with the Cartesian diver apparatus and compared with that of blastocysts from mammals where implantation is not delayed (rabbit, nonlactating rat). In general, there is a variation in the respiratory rate between species and within a species but the oxygen consumption of the delayed blastocysts was not different from the non‐delayed ones. It was concluded that the control of the delay in implantation in the animals studied, does not lie in the realm of respiratory changes.
The mechanism of ciliary movement. III. Theory of suppression of reversal by electrical potential of cilia reversed by barium ions
Authors: Jahn Theodore L. 
Published: February 2005

AbstractIt is well known that Paramecium (1) is cathodally galvanotactic in mixtures of sodium and calcium salts because of ciliary reversal at the cathodal end, and that (2) the cilia also may be reversed in solutions rich in monovalent cations or in barium or manganese ions, and (3) the organisms swim backward in these solutions.It also is well known (Kamada, '31) that Paramecium in solutions of barium salts (4) is anodally galvanotactic at low electric potentials, (5) is cathodally galvanotactic at higher potentials, and (6) again becomes anodally galvanotactic if the potential is lowered, but these results have never been explained.However, they can be explained if the membrane is assumed to act as an ion exchanger. Cilia are reversed by barium because barium replaces some of the calcium on the membrane. When a low cathodal potential is applied, the barium, because of its high electrophoretic velocity (Ba++> Ca++> Na+) is removed, thereby causing a suppression of the reversal. If the potential is increased, calcium is also removed, leaving mostly sodium on the membrane, and this causes a return of the reversal. Lowering the potential again causes a suppression of the reversal. Changes at the anodal end can be explained in a comparable manner.
Evidence implicating a membrane ATPase in the control of passive permeability of excitable cells
Authors: Bowler K. , Duncan C. J. 
Published: February 2005

AbstractThe temperature sensitivity of the ATPase enzyme systems in a muscle microsomal preparation from the crayfish, Astacus pallipes, was studied. Preincubation of the enzyme preparation in the range 33–36°C produced a marked inactivation of the ATPases; the Mg++‐dependent ATPase was very much more sensitive to this treatment than the Na+‐K+‐Mg++‐dependent ATPase. Thus, the Arrhenius μ for the inactivation of the Mg++‐dependent ATPase produced by eight minute preincubation is > 100 Kcals. These results are compared with the changes that are observed during the heat death of the whole animal, where exposure to 35°C produces a dramatic change in Na+ permeability within five minutes. Arrhenius μ for heat death is also > 100 Kcals and operates over the identical critical temperature range. It is suggested that the Mg++‐dependent ATPase controls passive permeability in these excitable cells and the results also confirm the view that Mg++ and Na+‐K+‐Mg++ ATPases are separate enzymes.
Amino acid requirements for growth of the rabbit blastocyst in vitro
Authors: Daniel Joseph C. , Krishnan R. Sivarama 
Published: February 2005

AbstractTen amino acids, namely, arginine, histidine, lysine, tryptophane, methionine, phenylalanine, leucine, valine, threonine and serine were indispensable for growth of rabbit blastocysts in vitro; others were nonessential. Of all the essential amino acids, arginine and lysine were required in relatively high concentrations, 10−2 M and 10−3 M, respectively, for optimum growth. Complete omission of the non‐essential amino acids from the medium markedly reduced blastocyst growth. Interaction between serine and glycine demonstrated a partial sparing action on serine by glycine, similar to that observed between methionine and cysteine. The amino acid composition of a culture medium capable of providing continuous and consistent growth of rabbit blastocysts in vitro is described.
Evidence for dual physiological forms of ergosterol in Saccharomyces cerevisiae
Authors: Adams B. G. , Parks L. W. 
Published: February 2005

AbstractData obtained from acid hydrolysis and extraction of yeast have demonstrated that routine saponification does not recover total sterol from the cells. This suggests the existence of a form of ergosterol resistant to saponification. Time course analyses of sterol synthesis by resting cell suspensions reveal an inverse relationship between the amounts of base labile and acid labile forms of sterol. These data give strong presumptive evidence for dual forms of ergosterol which are interconvertible according to the respiratory state of the cell.
Clonal growth of cells taken directly from adult rabbits
Authors: Ham Richard G. , Murray Louann W. 
Published: February 2005

AbstractSingle cell suspensions were prepared from the choroids of adult rabbit eyes using Pronase digestion, gentle pipetting and centrifugation. When diluted and inoculated into medium F12 supplemented with 5% fetal bovine serum and 10% rabbit serum, the choroid cell suspensions yielded large, healthy colonies with an average plating efficiency of about 45%. The growth in culture of a large portion of the cells from a normal non‐embryonic tissue opens new possibilities for the study of cellular differentiation in vitro.
The cytogenetic effects of mycoplasma in human leukocyte cultures
Authors: Aula Pertti , Nichols Warren W. 
Published: February 2005

AbstractTo evaluate the possible role of mycoplasma contamination of tissue cultures in virus induced chromosome breakage, human leukocyte cultures were inoculated with three mycoplasma strains; M. salivarium, M. hominis type 2 and M. fermentans. All three strains caused mitotic inhibition when an inoculum of approximately 106 CFU was used, the effect of M. fermentans being less severe than the one produced by the two other strains. Using a lower inoculum of 103 CFU an increase of chromosome breakage could be produced with M. salivarium when the leukocytes were cultivated for five days. No chromosome changes were seen with M. hominis type 2 and M. fermentans.The mitotic inhibition and chromosome breaks induced by M. salivarium were discovered to be related to an arginine deficiency of the culture medium produced by the mycoplasma. This conclusion is dervied from the fact that arginine addition was able to inhibit the mitotic inhibition and the increase of chromosome breakage, and secondly, that similar changes could be produced in leukocytes grown in argining deficient medidum without mycoplasma.The growth of M. salivarium was inhibited in leukocyte cultures treated with kanamycin, but the mycoplasma induced mitotic inhibition was still present, indicating that replication of mycoplasma organisms was not required for the production of arginine deficiency.
Interferon induction and utilization
Authors: Hilleman M. R. 
Published: February 2005

AbstractThe interferon mechanism offers the hope for moderate to high level prophylactic immunity of broad antiviral spectrum but of relatively short duration. Economic and biological considerations offer little hope for utilization of exogenous interferon as a prophylactic or therapeutic substance, unless but a small part of the total molecule be found to carry the activity. The real promise for interferon application is in the administration of suitable inducers so as to cause the body to produce and distribute its own interferon. Certain ribonucleic acids (RNA's) offer hope for high level potency as inducers without adverse effect. The condition for interferon induction by ribonucleic acids appears to be double‐ or multistrandedness and freedom from inhibitors. These can be of biologic or synthetic origin. The mechanism of action of interferon is not fully understood but appears to fit into the Jacob‐Monod model involving two phases: first, a derepression by the inducer to cause the cell to form interferon and second, a derepression by interferon to cause recipient cells to form the active substance which acts by preventing translation from viral messenger RNA. Double or multistranded RNA of viral or other origin appears to be unique to the cell and serves as the alert to it to produce interferon in phase 1. Greatest need for interferon is clearly for those diseases in which there is a multiplicity of immunologic types in excess of the numbers which could be put into a vaccine as, e.g., the common cold and enteric viruses. There might be some overall therapeutic benefit also if inducer were given early enough in infection. Special value for interferon induction might derive by administration in early life before the development of immunologic maturity, as a means for preventing infection with oncogenic or other viruses. Additionally, suitable inducers might be capable of interrupting the reinfection cycle in virus‐dependent malignancies.The favorable outlook for interferon utilization must always be tempered with the realization that under certain as yet undiscovered situations, adverse rather than beneficial effects might result from indution of interferon. It is not impossible that in certain special circumstances, as in ordinary immunologic responses, it might be more beneficial to negate rather than to promote the effect.
Membrane potentials of human fibroblast strains in culture
Authors: Swift Michael R. , Todaro George J. 
Published: February 2005

AbstractWith a simple technique, the membrane electro‐physiology of mammalian fibroblasts in tissue culture can be explored with micro‐electrodes. Measured in complete, serum‐containing medium, the mean membrane potential for human diploid cell strains in between 70 and 75 millivolts.
Photoreactivation of amphibian cells in culture
Authors: Regan James D. , Cook John S. , Lee William H. 
Published: February 2005

AbstractPhotoreactivation of growth and DNA synthesis in UV‐irradiated cells and photoreactivating‐enzyme activity of cell‐free extracts can be demonstrated in a cell line derived from liver tissue of the African clawed toad, Xenopus laevis. This cell line, A8W2, is a favorable system for the quantitative study of photoreactivation in vertebrates.
Photo‐inhibition of cell division and growth in euglenoid flagellates
Authors: Cook J. R. 
Published: February 2005

AbstractVisible light of moderate intensity causes two and perhaps three types of division inhibition in Euglena gracilis are related cells. Fluorescent light causes a general inhibition of growth and division which is temperature‐dependent. Pigmentation or complex organic media partially lifts this inhibition. A second type of inhibition, which is transient, can be caused by either fluorescent or incandescent light, and is found with an irreversibly bleached strain of Euglena grown on a limiting concentration of acetate; this inhibition could not be demonstrated in cells grown on limiting concentrations of glucose.
Production of the inducer for macrophage and granulocyte colonies by leukemic cells
Authors: Paran Michael , Ichikawa Yasuo , Sachs Leo 
Published: February 2005

AbstractCell lines from a myeloid, an erythroid, and two lymphoid leukemias, were tested for the production of the inducer required for the formation of macrophage and granulocyte colonies. It was shown that the inducer was produced by all lines except one of the lymphoid leukemias.
Thymidine as a synchronizing agent. I. Nucleic acid and protein formation in synchronous HeLa cultures treated with excess thymidine
Authors: Studzinski George P. , Lambert W. Clark 
Published: February 2005

AbstractSynchronous cultures of HeLa cells obtained by selective detachment of mitoses were treated with high concentrations of thymidine. The inhibitor was added soon after completion of cell division and rates of cell enlargement and accumulation of DNA, RNA and protein were compared for untreated and thymidine‐treated cultures at various points of the cell cycle. It was found that concentrations of thymidine which in randomly growing cultures inhibit the rate of cell division by more than 90% allowed a considerable degree of DNA synthesis and did not affect the rate of accumulation of RNA and protein, when applied to cells in the G1 phase of synchronous culture. Treated and untreated cells enlarged at the same rate throughout their life cycle. The results show that concentrations of thymidine commonly employed to produce cell synchrony do not arrest the cells at the G1‐S boundary, but allow slow progress through S in respect to DNA synthesis, and near‐normal progress towards G2 as regards RNA and protein accumulation and cell enlargement.
Effect of estradiol on splenic repopulation by endogenous and exogenous hemopoietic cells in irradiated mice
Authors: Jenkins V. K. , Upton A. C. , Odell T. T. 
Published: February 2005

AbstractEstradiol treatment of irradiated mice during repopulation of their spleens by endogenous hemopoietic cells reduced the number of myelocytic colonies and increased the numbers of erythropoietic and undifferentiated colonies. The inhibitory effects of the hormone on myelopoiesis were not dependent on stimulation of erythropoiesis, since they occurred in the absence of erythropoiesis in mice made polycythemic by hypertransfusion.Treatment of bone marrow donors with estradiol reduced the ability of their marrow cells to form spleen colonies, particularly reducing the proportion of myelopoietic colonies relative to the total number of colonies of all types. Conversely erythropoietic colonies, though reduced in absolute number, were increased in relative number. Such treatment also decreased the volume and cell content of the marrow cavity through stimulation of endosteal bone formation.Estradiol treatment of lethally irradiated recipient mice did not detectably alter the total numbers or types of hemopoietic spleen colonies formed in these animals from transplanted marrow cells; however, without estradiol treatment, myelopoietic colonies were so few and erythropoietic colonies so numerous that the effects of the hormones may have been undetectable by the methods employed.The sex of the donor or recipient mouse did not affect the numbers or types of colonies formed, suggesting that endogenous levels of estradiol were too low to exert effects dectectable by the methods used. However, since our mice were only 8 weeks old, the data do not exclude the possibility that older female mice, with higher levels of estradiol, would have differed from males in relative numbers of myelopoietic as compared with erythropoietic colonies.
Ribonucleic acid within the extracellular matrix during embryonic tooth formation
Authors: Slavkin H. C. , Bringas P. , Bavetta L. A. 
Published: February 2005

AbstractDuring embryonic tooth formation, interactions between epithelial and mesenchymal cells results in the formation of a metachromatic interface or extracellular matrix. The cervical or germinative region of this epidermal organ system is populated by an increasing gradient of cellular differentiation and an extracellular matrix which is the progenitor for subsequent dentine organic matrix formation. Embryonic rabbit tooth primordia can be maintained in culture enabling kinetic studies of labeled precursor incorporation. Autoradiographs of tooth organ cultures continusly incubated with labeled uridine for periods up to eight hours, demonstrated initial cellular incorporation with subsequent transfer of 2% of the grain density to the extracellular matrix by four hours. The grain density was removed by ribonuclease treatment. No incorporation of tritiated thymidine into the matrix was observed. The incorporation of C14‐uridine during organ culture was inhibited by actinomycin D. Micrurgy was employed to isolate the extracellular matrix free of adherent cells. Electron microscopy demonstrated membrane‐bound, electron dense bodies within the matrix, presumably cytoplasmic extensions. No cells per se were observed on the isolated matrix. Several experimental criteria suggested that uridine incorporation into the extracellular matrix was regulated by epithelial and mesenchymal cells. Phenol extraction procedures of labeled cervical matrices demonstrated an ultraviolet absorption maximum at 260 μU. Both spectrophotometric determinations and orcinol assays found RNA to be 0.4–0.5% of the cervical extracellular matrix.These results are interpreted to indicate that RNA is a component of the metachromatic extracellular matrix during epithelio‐mensenchymal interactions associated with tooth formation. The functional significance of these observations is premature at this time.
Increased resistance of immature red cells of rat and dog to osmotic lysis
Authors: Sacher G. A. , Miller M. 
Published: February 2005

AbstractMature male rats were injected with radioiron, which labeled immature red cells that were in the stage of hemoglobin synthesis at the time. Washed cells were subjected to lysis by hypotonic saline at 14 intervals ranging from 1 to 85 hours after 59Fe injection. Lysis curves were determined colorimetrically (for the whole population) and by scintillation counting of 59Fe gamma rays (for the labeled population). Newly labeled rat red cells are much more resistant than mature erythrocytes. The mature curve of osmotic resistance is acquired about 67 hours after injection. The delivery of labeled cells continues for more than 36 hours, so the maturation of osmotic properties of a typical rat red cell takes about 30 hours from entry into the circulation. Washed dog cells behave in similar fashion but delivery continues for three days and the mature lysis curve does not appear until five days after labeling, so that maturation takes about two days. Preincubation of cells is requisite for the appearance of osmotic resistance, but the basis of the incubation effect is not yet known.
Stimulation of mitotic activity and the initiation of deoxyribonucleic acid synthesis in populations of rat thymic lymphocytes by magnesium
Authors: Whitfield J. F. , Perris A. D. , Rixon R. H. 
Published: February 2005

AbstractThe progression of rat thynocytes (maintained in vitro) into mitosis is profoundly affected by the level of magnesium in the medium. Increasing the extracellular MgC12 concentration from 0 to 1.0 mM does not affect mitotic activity, but a further increase to 1.2 and 2.5 mM rapidly and strongly stimulates the flow of cells into mitosis. The level of extracellular magnesium also governs the mitogenic effectiveness of calcium ions. The mitogenic action of magnesium stems from an ability to stimulate the initiation of deoxyribonucleic acid synthesis.