bluuebunny/crossref_metadata_2025_split huggingface dataset:
Control of mating type expression in Paramecium multimicronucleatum, syngen 2
Authors: Clark Mary Anne 
Published: February 2005

AbstractTwo isogenic acyclic strains of Paramecium multimicronucleatum, syngen 2, expressing mating types III and IV, and a cycler strain, which displays circadian alternation of the two mating types, were treated with proteolytic enzymes, or the inhibitors actinomycin D or puromycin at various stages of the mating reactive period induced by food depletion. Reactivity of acyclic animals was sensitive to proteolytic enzymes, and to both inhibitors before or after the onset of reactivity, suggesting that reactivity is attained and maintained via continuous RNA and protein synthesis, and that protein integrity is essential to the activity of the type‐specific substances. A new cell cycle was not necessary for recovery from a block in reactivity.Type III animals were consistently more sensitive to inhibition by puromyin, and required longer recovery periods after all treatments except actinomycin D given after the development of reactivity. Possible explanations of these observations are considered.The daily type changes seen in cycler animals seemed to occur by replacement of one mating type substance with the other. Type‐switching was neither prevented nor displaced by exposure to actinomycin D or puromycin during a period before or including a type change, even though reactivity was reduced by more than 95%, suggesting that type‐switching is not directly associated with transcription or translation of the type‐specific genes.
Measurement of the size distribution of human erythrocytes by a sedimentation method
Authors: Groom A. C. , Anderson J. C. 
Published: February 2005

AbstractThe distribution of sedimentation velocities was determined, by a photoelectric method, for human erythrocytes at low concentrations in Ringer solution. The light absorption at 414 nm was measured, as a function of time, 10 mm below the top of the column. From the frequency distribution of cell velocities that of Rs √ρ‐σ was found; Rs being the Stokes' radius, ρ the cell density and σ the density of the solution. Cell density was measured by the phthalate method and the mean Stokes' radius was found to be 2.58 μm. The size distributions showed some skewness but were in good general agreement with those measured by Celloscope counter, and with reported measurements from photomicrographs of cells in hanging drop suspensions. The skewness was much less than that encountered with electric sensing zone instruments (e.g. Celloscope) and the sedimentation method, being based on entirely different premises, provides an important check on such data. The skewness is due to a bias in the orientation of human erythrocytes during sedimentation. This bias may be a characteristic of biconcave cells; it could be absent in many species and reliable measurements of size distribution would then be obtained.
The role of cell‐cell contact in “contact” inhibition of cell division: A review and new evidence
Authors: Martz Eric , Steinberg Malcolm S. 
Published: February 2005

AbstractThe term “contact inhibition of cell division” was borrowed from “contact inhibition of cell movement.” We prefer the term “postconfluence inhibition of cell division” as being more operational and less mechanistically biased; it is operationally defined as a pronounced depression of the mitotic rate in a postconfluent culture which displays a stationary density despite periodic nutrient renewal, the inhibition being locally reversibly by removal of the adjacent cells.The mechanism of postconfluence inhibition is of considerable interest because of the inverse correlation between postconfluence inhibition and the tumorigenicity of a number of cell lines. Several hypotheses, involving direct cell‐to‐cell contacts or locally restricted diffusion gradiens, could explain postconfluence inhibition.With the goal of discriminating among these hypotheses, time‐lapse films were taken of carefully regulated, perfused cultures of 3T3 mouse cells, in which the transition from rapid growth to the stationary phase was recorded. Measurements of cell‐to‐cell contact, local cell density, and generation times were made on an individual cell level and analyzed with the aid of a computer.We observed that all‐around cell‐cell contact or a high local cell density present throughout G1 often did not produce immediate inhibition of cell division. We conclude that either (i) simple visible cell‐cell contacts or a high local cell density are not the direct cause of postconfluence inhibition of cell division, or (ii) their effects often do not inhibit cell division until after a delay of about one cell generation time. Such a delay may be partly responsible for the 50% overshoot past the stationary density that we observed in 3T3 cultures.
Studies on the surface of chick blastoderm cells. II. Electron microscopy of surface binding characteristics
Authors: Sanders Esmond J. , Zalik Sara E. 
Published: February 2005

AbstractThe surfaces of cells from the early embryo of the chick were examined with the electron microscope using histochemical techniques in order to determine the distribution of cell surface material. The use of lanthanum nitrate as a stain for protein‐polysaccharide showed that in whole embryos the surface layer was present in areas of close membrane apposition, but relatively sparse where the membranes bounded large intercellular spaces. On cells freshly dissociated with EDTA, this technique demonstrated a very uniform layer over the surface, possibly indicating some redistribution. Close examination of the lanthanum stained material in whole embryos revealed the presence of periodicities about 180 Å in diameter.In correlation with a progressive reduction of electrophoretic mobility, demonstrated previously, from embryonic stage 1 to stage 5, some decrease in the affinity of the surface for lanthanum and colloidal iron was observed.
Induction of erythroblast increase in rabbit marrow cells by extracts of leukocytes and certain metabolic compounds. IV. Studies on erythropoiesis
Authors: Borsook Henry , Jiggins Susan , Wilson Rosina T. 
Published: February 2005

AbstractTwo kinds of extracts of peripheral blood leukocytes induced erythroblast increase and maturation in vitro in rabbit marrow cells. One extract was a secretion or exudate into plasma from intact leukocytes; the other was the supernatant after homogenizing the cells in ethanol. The extracts were less active than the intact leukocytes. The response with the two extracts together was a little greater than with either alone, but less than additive.11‐Ketopregnanolone and 3′5′ cyclic AMP were active inducers. Neither increased the effects of leukocytes or their extracts.
The mechanism of regulation of fibroblastic cell replication. I. Properties of the system
Authors: Ellem K. A. O. , Mironescu Stefan 
Published: February 2005

AbstractSixty to eighty per cent of the cells in a culture of human diploid fibroblasts may be stimulated from the state of density dependent inhibition of replication to active DNA synthesis and division. The maximum response is effected by 50% serum within the pH range 7.2–8.0. The proportion of cells responding depends on the concentration of serum protein in the medium which may be effectively substituted by crystalling serum albumin. There is a differential sensitivity to the stimulus of cells in the densely packed centers of whorls and in the less dense areas between the whorls. The cell response is parasynchronous and the median durations of the various phases of the cell cycle are: G1I6β Œæ® ¿ ∞ 8 hours, G2 = 6 hours and doubling time = 30 hours.The stimulatory effect of fresh medium is lost during contact with dense cultures so that it has only 50% of its initial capacity after 14 hours. It can be restored by dialysis against serum‐free medium. The stimulus must be applied for at least ten hours to be effective in inducing DNA synthesis. During the latter half of ten hour induction period subsequent DNA synthesis becomes exquisitely sensitive to actinomycin D. After this time an increasing number of cells become irreversibly committed to replicate. The data are interpreted to indicate that during contact with serum proteins (including albumin) changes in the cell surface, if continued long enough, trigger a mechanism which involves the synthesis of a unique RNA species during the fifth to tenth hours. After this RNA has been synthesized the cells are then committed to DNA synthesis.
Lesch‐Nyhan mutation: The influence of population density on purine phosphoribosyltransferase activities and exogenous purine utilization in monolayer cultures of skin fibroblasts
Authors: Wood Stephen , Pinsky Leonard 
Published: February 2005

AbstractIn extracts of normal and Lesch‐Nyhan (LN) heterozygous skin fibroblast monolayer cultures, hypoxanthine‐guanine (H‐G) and adenine (A) phosphoribosyltransferase (PRT) activities are correlated. These activities vary concomitantly during the life cycle of a culture: Peak activities occur during exponential growth. The ratio of H‐GPRT to APRT activity can manifest heterozygosity at the LN locus when H‐GPRT activity, per se, is close to and unreliable different from the normal range.If 2 or 8 × 104 cells are planted per 35 mm petri dish, a strain with clearly heterozygous levels of H‐GPRT activity in its cell extract may not reveal its genotype by simultaneous measurement of adenine and hypoxanthine incorporation into its acid‐insoluble fraction one day after subculture. In contrast, a 1:1 coculture of normal and mutant cells yields the ratio of adenine to hypoxanthine incorporation expected from the behavior of each cell type separately. In heterozygous cultures at the higher population density, the incorporation of hypoxanthine relative to adenine is 28% greater than in those at the lower population density. A 1:1 mixture of normal and mutant cells exhibited a 20% increase in the relative incorporation of hypoxanthine over the same four fold increase in population density. These observations appear to provide a quantitative expression of the phenomenon of metabolic cooperation between contacting H‐GPRT‐negative and H‐GPRT‐positive cells.
Incorporation and intraparticulate hydrolysis of 131 I‐albumin by liver and kidney of an amphibian (Bufo arenarum)
Authors: Bertini Francisco , Bari Daniel R. , Mazzei Hector 
Published: February 2005

AbstractAfter a single injection of formaldehyde‐treated 131 I‐albumin into the heart, the incorporation of the labelled protein by liver (% of total injected radioactivity/% of body weight of the organ) was far greater than in other organs. In kidney and spleen it was respectively six and three times greater than in lungs, intestine, testis and fatty body. No radioactivity was found in brain. The radioactivity in liver and kidney reached a peak 30 minutes after the injection, and quickly decreased during the following four hours. In the 27,000 g × ten minute particles recovered from liver homogenates of animals sacrificed at various times after injection, the rate of 131 I‐albumin hydrolysis in vitro and the percentage of trichloroacetic acid soluble radioactivity at zero time of incubation showed different stages of intraparticulate hydrolytic activity. The incorporation and intraparticulate hydrolysis in toad kidney was very low if compared with that of toad liver or mouse kidney; however the catheptic specific activity in toad kidney doubles that of mouse kidney. Isolated toad liver was perfused with total blood, containing 131 I‐albumin, for five hours at 22°C in a special chamber. In this conditions, 16% of the labelled albumin was hydrolyzed by the liver.
Regulation of mitochondrial respiration in senescence
Authors: Chen Jenn C. , Warshaw Joseph B. , Sanadi D. Rao 
Published: February 2005

AbstractThe ADP‐stimulated (State 3) respiration of myocardial mitochondria with glutamate‐malate, glutamate‐pyruvate, palmitylcarnitine and β‐hydroxybutyrate as substrates declined in rats after the age of 20 months. There was no significant decline in pyruvate‐malate, α‐oxoglutarate, palmityl‐CoA, succinate and ascorbate cytochrome c oxidation. Skeletal muscle mitochondria from senescent animals showed a similar decline in glutamate‐malate oxidation but not in palmityl‐CoA, palmitylcarnitine, succinate and ascorbate‐cytochrome c oxidation. The controlled oxidation with ADP‐limiting (State 4) and the ADP/O ratio were not affected. The results indicate an alteration in the subtle regulatory capacity for mitochondrial oxidation in senescent rats. It is suggested that the alteration may be in certain anion transport and associated functions across the mitochondrial membrane or dehydrogenase activity.
Effects of prednisolone on the distribution and activity of two phosphoesterases in membrane preparations from HeLa cells
Authors: Costlow Mark E. , Melnykovych George 
Published: February 2005

AbstractActivities of two membrane associated enzymes, viz. 5′‐nucleo‐tidase (EC 3.1.3.5) and alkaline phosphatase (EC 3.1.3.1) are known to be altered by glucocorticoid treatment of cells in culture. In certain HeLa cell lines, their activity is elevated, while in others, it is decreased. In order to confirm the data obtained previously with cell homogenates, cells were fractionated essentially as described by Bosmann, Hagopian and Eylar ('68) after 96 hours exposure to 0.5 μg/ml prednisolone. This treatment resulted in changes both in the specific activity and in the distribution of the two enzymes among the isolated membrane fractions. The alterations in specific activity in the individual membrane fractions reflected changes previously observed in preparations from whole cells. A shift in distribution of total enzymatic activity to fractions of higher density occurred in both cell lines in response to the steroid. These results may be indicative of cellular membrane alterations as a consequence of steroid treatment.
Formation in agar of fibroblast‐like colonies by cells from the mouse pleural cavity and other sources
Authors: Metcalf Donald 
Published: February 2005

AbstractColonies of elongated fibroblast‐like cells (stellate colonies) developed in agar cultures of mouse pleural cavity cells mixed with whole blood. Cultures of pleural cells alone developed only abortive clusters of round cells. The frequency of colony‐forming cells in the pleural cavity was highest in neonatal mice (200/105 cells) and fell progressively with aging. Stellate colony‐forming cells were not in cell cycle but were radiosensitive. In adult mice, only occasional colony‐forming cells were detected in peritoneal cavity, thymic, spleen, lymph node or bone marrow cell populations. Stellate colony formation was not stimulated by the granulopoietic regulator, colony stimulating factor. The active component in whole blood required for stellate colony formation was present in plasma but not serum or washed red or white cells.
Multiplication‐stimulating activity for chicken embryo fibroblasts from rat liver cell conditioned medium: A family of small polypeptides
Authors: Dulak Norman C. , Temin Howard M. 
Published: February 2005

AbstractA partially purified multiplication‐stimulating activity for chicken embryo fibroblasts in cell culture was isolated from rat liver cell conditioned medium (see preceding paper, Dulak and Temin, 1973). It has been analyzed by isoelectric focusing and by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Multiplication‐stimulating activity resided in a family of at least four polypeptides which were similar in apparent molecular size, but different in electrical charge. These polypeptides have a specific activity of about 50,000 with respect to serum. One of them has been purified on a small scale to apparent homogeneity in a sodium dodecyl sulfate polyacrylamide gel.
On the kinetics of erythroid cell differentiation in fetal mice. I. Microspectrophotometric determination of the hemoglobin content in erythroid cells during gestation
Authors: Steiner Rudolf , Vogel Helmut 
Published: February 2005

AbstractIn a microspectrophotometric study, photographic emulsions and a computer are used for measuring the hemoglobin content of a large number (about 50,000) of erythroid cells in fetal mice. Histograms of the hemoglobin content in erythroid cells illustrate the kinetics of erythropoiesis in yolk sac derived nucleated cells in the fetal peripheral blood, in fetal liver, and in fetal spleen. After the occasional extrusion of their nucleus, yolk sac derived erythrocytes remain as “macrocytes” in fetal circulation two or three days longer than the nucleated yolk sac derived erythrocytes do. Erythrocytes in fetal liver have a constant hemoglobin content of 28 pg 2 until day 17 of gestation. During further erythropoiesis in liver and then in the spleen, this amount is gradually adapted to the normal hemoglobin content in red blood cells of 16 pg.
Erythropoietic progenitors capable of colony formation in culture: State of differentiation
Authors: Gregory C. J. , McCulloch E. A. , Till J. K. 
Published: February 2005

AbstractThe differentiated state of mouse erythropoietic progenitor cells (CFU‐E), detected by their ability to form erythropoietin‐dependent colonies in vitro, has been investigated. Transfusion‐induced plethora was found to reduce the population size of CFU‐E in both spleen and femoral marrow, which indicates that a significant number of CFU‐E arise by differentiation processes that are themselves erythropoietin‐dependent. Individual spleen colonies were found to be heterogeneous in their content of CFU‐E, and the numbers of CFU‐E per colony were not correlated either positively or negatively with the numbers of granulocyte‐macrophage progenitors (CFU‐C) present in the same colonies. The absence of a negative correlation between CFU‐E and CFU‐C indicates that the erythropoietic and granulopoietic pathways of differentiation are not mutually exclusive within individual spleen colonies. The numbers of CFU‐E per spleen colony were also found to vary independently of the numbers of pluripotent stem cells (CFU‐S) per colony; in contrast, as found previously, the numbers of CFU‐C and CFU‐S per colony were positively correlated. These results indicate that more randomizing events separate CFU‐E from CFU‐S than separate CFU‐C from CFU‐S, and are consistent with the view that CFU‐E occupy a position on the erythropoietic pathway of differentiation that is more remote from the pluripotent stem cells than is the corresponding position of CFU‐C on the granulopoietic pathway.
Characteristics of calcium accumulation by lymphocytes and alterations in the process induced by phytohemagglutinin
Authors: Whitney Richard B. , Sutherland Robert M. 
Published: February 2005

AbstractCalcium uptake by normal human lymphocytes was found to be a saturable process which was competitively inhibited by manganese indicating the existence of a carrier‐mediated mechanism for calcium uptake. Exchange diffusion was not observed, Phytohemagglutinin (PHA) significantly stimulated calcium uptake within minutes after treatment. The increased uptake was attributed to a decreased Km for the proposed membrane carrier rather than to an increased Vmax. Also PHA did not stimulate a normally unused exchange diffusion process, nor did it affect calcium efflux. Uptake by both unstimulated and PHA‐treated lymphocytes was not influenced by magnesium or by cycloheximide or actinomycin D.
Cell division, ciliary regeneration and cyclic amp in a unicellular system
Authors: Wolff Jason 
Published: February 2005

AbstractIt is possible, by direct measurements, to demonstrate the presence of cyclic AMP in Tetrahymena. Its presence in a unicellular eukaryote suggests a fundamental role in cellular metabolism independent of its function as a “second messenger.” Caffeine, an inhibitor of phosphodiesterase, raises the intracellular concentration of cyclic AMP and causes an inhibition of cellular division. Dibutyryl cyclic AMP also causes a partial inhibition of proliferation and is potentiated by caffeine. Inhibited cells do not recover spontaneously during continued exposure to caffeine but the inhibition is reversible resulting in a synchronous wave of division peaking one generation time after return to fresh medium.Synchronous cells subjected to pulses of caffeine at various intervals of the cell cycle are set back in time as measured by the excess division delay. There is a linear relationship between the age of the cells at the pulse and the duration of the excess division delay such that the older the cells are the greater is the setback.Caffeine and dibutyryl cyclic AMP inhibit ciliary regeneration as does also deuterium oxide.
Effect of fluoride and other metobolic inhibitors on intracellular sodium and potassium concentrations in l cells
Authors: Quissell D. O. , Suttie J. W. 
Published: February 2005

AbstractFluoride, iodoacetate, oxamate, 2,4‐dinitrophenol, cycloheximide, and ouabain were studied to determine if any of these inhibitors affected the intracellular concentration of sodium and potassium in an L cell strain of mouse fibroblasts and to determine if the changes observed in these parameters could be correlated with growth rate. The results indicated that (1) the intracellular concentration of sodium and potassium could not be correlated with growth rate, (2) fluoride, iodoacetate, oxamate, 2,4‐dinitrophenol, and cycloheximide at concentrations having an equal effect on growth had a similar effect on the intracellular sodium and potassium concentration These changes were not as great as those seen with ouabain, which at a concentration which did not inhibit growth, had an equal or greater effect on the intracellular sodium and potassium concentration.
Proteins from melanosomes of mouse and chick pigment cells
Authors: Doezema Philip 
Published: February 2005

AbstractPurified subcellular fractions containing melanosomes from B‐16 mouse melanoma were treated with 2% sodium dodecyl sulfate or 0.5 M sodium hydroxide to dissolve protein. Quantitative measurements indicate that each melanosome contains 0.065×10−10 of protein or about 19% by weight. SDS acrylamide gel electrophoresis of proteins from purified melanosomes resolved six polypeptide bands of major density and about 15 minor bands. These results indicate that the melanosome may be more complex than previous genetic, biochemical or morphological evidence had suggested.
Sedimentation velocity characterisation of the cell cycle of granulocytic progenitor cells in monkey hemopoietic tissue
Authors: Williams Neil , Moore Malcolm 
Published: February 2005

AbstractSedimentation velocity separation of Rhesus monkey bone marrow cells has demonstrated a reproducible but heterogeneous size distribution of cells capable of forming granulocytic colonies in agar culture (CFC's). This heterogeneity is shown to be due to the cell cycle status of the progenitor cell population. In vitro exposure of bone marrow cells to lethal doses of tritiated thymidine (H3TdR) either before or after separation restricts the size distribution of CFC's, greatly reducing the proportion of rapidly sedimenting cells. The calculation of the volume distribution of such cells before and after H3TdR exposure indicates that 55% of total CFC's in adult marrow are in G0 or G1 with a volume of 410 μ3, 42% are in S phase and of volume 450–950 μ3, and the remainder are in G2 and mitosis with a volume of between 600–950 μ3. CFC's in mid gestation fetal liver were larger than their adult counterparts and were of homogeneous volume indicative of a single non cycling population with no evidence of an S or G2 component. H3TdR exposure confirmed the non‐cycling status of these fetal progenitor cells.