bluuebunny/crossref_metadata_2025 huggingface dataset:
The glyceride fatty acid composition and lipid content of brown and white adipose tissue of the hibernator Citellus lateralis
Authors: Spencer W. A. , Grodums E. I. , Dempster G.
Published: February 2005

Glyceride and total phosphatide levels of brown and white fat of Citellus lateralis have been followed throughout the year in biopsy samples.

Extraction of the glycerides for fatty acid analysis is described. As much as 20% of the phosphatide of brown fat was found in the upper fat layer of a centrifuged tissue homogenate. This phosphatide appeared to be present as a low‐density lipoprotein, and may be associated with the lipid globules of the intact cell.

Glyceride and phosphatide levels varied considerably in brown fat, and no particular level was consistently observed to be associated with any part of the hibernation cycle. Fatty acid composition of the glycerides also varied widely. The degree of unsaturation was not related to the hibernation cycle, although there appeared to be a differential utilization of fatty acids during a few weeks prior to spring arousal.

A decrease in tissue glyceride levels was observed in both brown and white fat during arousal from hibernation at 2°C, the loss from brown fat being double the loss from white fat.
Electrophoretic mobility of mouse cells and homologous isolated nuclei
Authors: Mayhew E. , Nordling S.
Published: February 2005

The electrophoretic mobilities of Ehrlich ascites, sarcoma 37 ascites, mouse liver cells and their isolated nuclei were measured under similar environmental conditions. No differences in mobility were detected between cells and homologous nuclei from the same cell population and it was concluded that their surface charge densities were probably the same. The effect of neuraminidase on Ehrlich ascites and liver cells and nuclei was also determined; neuraminidase reduced the mobility of Ehrlich ascites cell nuclei as well as cells. The reduction in mobility of cells and nuclei prepared by a sucrose method was the same; however, the reduction in mobility of citric acid prepared nuclei was less than that of citric acid treated cells. The reduction in mobility of both liver cells and nuclei was small or insignificant. It is suggested that although cells and nuclei have similar electrophoretic mobilities, possibly different groups contribute to their surface charge.
Cholinesterase activity of isolated giant synapses
Authors: Bryant S. H. , Brzin M.
Published: February 2005

Isolated single giant synapses from the squid stellate gangalion, analyzed for cholinesterase activity with the microgasometric magnetic diyer method had a high activity compared to that of pieces of pre‐ and postsynaptic axons.
Effects of inhibitor, competitors and temperature on transport of carbohydrate in Crithidia luciliae
Authors: Min Hong S.
Published: February 2005

Effects of KCN (10−4 M), simultaneous presence of varying concentrations of D‐glucose and L‐sorbose, and temperature on transport of carbohydrate in C. luciliae have been studied. The rate of carbohydrate entrance is inhibited, in all sugars used, ranging from 19% to 70% inhibition at 0.5 mM external concentrations. However, this inhibitor does not affect transport from external concentrations of the order of 0.02 M. At 20 mM external concentration, the rate of L‐sorbose entrance is greatly inhibited by the simultaneous presence of D‐glucose, and the transport mechanism shows enormously greater affinity for glucose than for other monosaccharides. However, at 0.5 mM external concentration, the rate of sorbose entrance is not inhibited at all by the simultaneous presence of D‐glucose. In the temperature interval 15°–25°C, the Q10 for rate of entrance when the external concentration is 0.5 mM is 2.8 times larger than the Q10 when the external concentration is 20 mM. These data are interpreted as strongly suggesting two mechanisms for carbohydrate entrance: (a) facilitated diffusion, of importance only at high external concentrations; (b) an active transport mechanism, active at low external concentrations and dependent upon a supply of metabolic energy. These results are compared with those reported in the literature for other types of cells.
Amino acid requirements for attachment and outgrowth of the mouse blastocyst in vitro
Authors: Gwatkin R. B. L.
Published: February 2005

Arginine, cystine, histidine, leucine and threonine were needed for outgrowth of the mouse blastocyst in vitro. Omission of lysine, methionine, phenylalanine, tryptophane and tyrosine from the culture medium markedly reduced blastocyst outgrowth, but did not inhibit it completely; while omission of isolecine and valine reduced the extent of outgrowth only slightly. Blastocysts kept for seven days in a free‐floating condition by omitting arginine and leucine from the medium, grew out when these amino acids were added. Such behavior may be analogous to delayed implantation in utero and suggests that the free amino acid content of the uterus could be an important factor in the control of implantation. Blastocysts delayed from implanting in the uterus by ovariectomy were activated to outgrowth in a complete medium, but the intracellular changes associated with outgrowth occurred more slowly than in undelayed blastocysts.
The presence of ribonucleic acid within the peripheral zones of two types of mammalian cell
Authors: Weiss L. , Mayhew E.
Published: February 2005

An attempt has been made to locate RNA as a structural component of the peripheries of cultured cells derived from a human osteogenic sarcoma, and L1210 mouse leukaemia cells. In the case of cells derived from the osteogenic sarcoma, their detachment from glass was facilitated by incubation with ribonuclease; on removal from glass, they left cellular “footprints” behind, which were visulized in radioautographs of cells previously labeled with tritiated uridine, and removable with ribonuclease. The electrophoretic data show loss of charge by both types of cell following incubation with ribonuclease.

These results are interpreted to indicate that RNA is a structural component of the peripheries of these cells. No attempt is made to speculate on the obvious biological improtance of these observations if they are applicable to cells in general.
Stimulation by normal and leukemic mouse sera of colony formation in vitro by mouse bone marrow cells
Authors: Robinson W. , Metcalf D. , Bradley T. R.
Published: February 2005

Using a modification of the agar gel method for bone marrow culture, serum from various strains of mice has been tested for colony stimulating activity. Ninety percent of sera from AKR mice with spontaneous or transplanted lymphoid leukemia and 40–50% of sera from normal or preleukemic AKR mice stimulated colony formation by C57B1 bone marrow cells. Sera from 6% of C3H and 30% of C57B1 mice stimulated similar colony formation. The incidence of sera with colony stimulating activity rose with increasing age. All colonies were initially mainly granulocytic in nature but later became pure populations of mononuclear cells.

Bone marrow cells exhibited considerable variation in their responsiveness to stimulation by mouse serum. Increasing the serum dose increased the number and size of bone marrow cell colonies and with optimal serum doses, 1 in 1000 bone marrow cells formed a cell colony. Preincubation of cells with active serum did not stimulate colony formation by washed bone marrow cells.

The active factor in serum was filterable, non‐dialysable and heat and ether labile.
Analysis of colonies developing in vitro from mouse bone marrow cells stimulated by kidney feeder layers or leukemic serum
Authors: Metcalf D. , Bradley T. R. , Robinson W.
Published: February 2005

An analysis has been made of cell colonies developing in agar cultures from mouse bone marrow cells following stimulation either by neonatal kidney cell feeder layers or AKR lymphoid leukemia serum. Colonies arose by cell proliferation and were mixtures of granulocytic and mononuclear cells.

Colonies stimulated by kidney feeder layers reached a mean size of 2000 cells by day 10 of incubation and remained predominantly granulocytic in nature. When bovine serum was substituted for fetal calf serum, cell colonies grew to a smaller size and lost their granulocytic nature, finally becoming almost pure populations of mononuclear cells.

Colonies stimulated by AKR leukemic serum reached a mean size of 350 cells by day 10 of incubation. Although these colonies initially were granulocytic in nature, they finally became almost pure populations of mononuclear cells.

The colony mononuclear cells actively phagocytosed carbon, and contained metachromatic granules probably derived from ingestion of agar.

The mononuclear cells in these colonies may not have been members of the original colony, but may have been incorporated in the colony as it expanded in size, subsequently proliferating in the favourable environment of the colony.
Some physicochemical factors relevant to cellular interactions
Authors: Brooks D. E. , Millar J. S. , Seaman G. V. F. , Vassar P. S.
Published: February 2005

Colloidal stability theory is discussed to accomodate the conditions imposed by biological systems. It is shown that to obtain potential curves with secondary minima, Hamaker's constant must be in the range of 1–5 × 10−14 ergs. The effect of increasing the dielectric constant is shown in theory to lower the surface potential and electrophoretic mobility but to increase the total energy of interaction. Calculations made from the theory predict the forces between model cells to be ca. 4.0 × 10−7 dynes.

By cone‐plate shearing of cell aggregates, the most successful of several techniques tried and discussed, at shear rates approaching 1 × 10−4 second−1 (1.5 × 10−4 dynes) semi‐complete disaggregation was achieved although cell disruption was apparent; analysis of blood viscosity data indicates 5–10 × 10−7 dynes are required to separate red cells suspended in plasma. Colloidal stability theory, while not applicable to cell systems associated by special areas of attachment, seems to describe the physicochemical interaction of freely moving or reversibly adherent cells.
Observations and measurements of sea urchin eggs with a centrifuge microscope
Authors: Hiramoto Y.
Published: February 2005

Eggs of the sea urchins, Arbacia punctulata and Lytechinus variegatus were observed with a centrifuge microscope. The protoplasmic viscosity calculated from the displacement velocity of the nucleus in a centrifugal field is about 30 poises. The surface forces of the unfertilized egg, which were determined from the relationship between the deformations of the egg in centrifugal fields and the magnitudes of the centrifugal forces, are 0.046 dyne/cm in Arbacia and 0.087 dyne/cm in Lytechinus (mean values). Both of these values increase as the deformation of the egg increases. The cleavage plane of the first cleavage of the egg in the centrifugal field (35–140 × g) is parallel to the direction of the centrifugal force. The flattening of the fertilized egg in a constant centrifugal field changes during development, probably owing to the change in the surface force. The flattening attains a minimum shortly before the onset of cleavage and another minimum during the cleavage, corresponding to a peak of the surface before the cleavage and another peak during the cleavage.
DNA synthesis in the giant salivary chromosomes of Drosophila virilis prior to pupation
Authors: Pettit Barbara J. , Rasch Robert W. , Rasch Ellen M.
Published: February 2005

Both two‐wavelength microspectrophotometry of Feulgen‐stained whole nuclei and autoradiography of H3‐thymidine incorporation by giant salivary chromosomes in Drosophila virilis demonstrate a net decrease in the relative rate of salivary DNA synthesis during the late third instar and prepupal stages of development. Amounts of DNA‐Feulgen per nucleus were distributed into several classes, the means of which closely approximated values projected as geometric multiples of the basic somatic DNA level estimated from hemocyte nuclei of the same larvae. Comparison of DNA polytene class frequencies showed no statistical difference between male larvae of different development stages, although female prepupae showed a greater frequency of nuclei in higher polytene classes when compared to male prepupae of the same age. Comparison of chromosomal H3‐thymidine incorporation with previously described H3‐histidine incorporation suggests that the amino acid labeling, which reaches a maximum during the prepupal period, has a physiological significance distinct from chromosomal endoreplication.
Effect of ribonuclease and neuraminidase on the electrophoretic mobility of tissue culture cells in parasynchronous growth
Authors: Mayhew E.
Published: February 2005

Cultured mammalian cells (RPMI no. 41) in parasynchronous growth were treated, at different stages of the mitotic cycle, with neuraminidase and ribonuclease, separately and sequentially, and their electrophoretic mobilities determined. Changes in the electrophoretic mobility of these cells are probably mainly due to variations in the density of negatively charged groups susceptible to neuraminidase, although variations in groups susceptible to ribonuclease may occur. It is suggested that the observed variations in electrophoretic mobility of different cells may be due to differences in the relative lengths of different life‐cycle phases. Where G2 phase is relatively long or G1 relatively short the cell populations will hve higher mean electrophoretic mobilities.
Calcium binding by subcellular fractions of bovine adrenal medulla
Authors: Borowitz J. L.
Published: February 2005

Significantly more calcium per gram protein was found in a relatively pure granule fraction isolated from fresh bovine adrenal medulla than in predominantly mitochondrial fractions isolated from the same tissue. Sixty‐four and 55% of the calcium associated with chromaffin granule and mitochondrial fractions, respectively, was released into the supernatant upon lowering the tonicity of the medium. The per cent calcium released by this procedure was significantly greater for granules than for mitochondria (p < 0.05). The amount of calcium per gram protein released into the supernatant also was greater in granule fractions than in mitochondrial fractions (p < 0.05). These data, coupled with a previous report that 10−3 M EDTA does not markedly decrease the calcium content of whole granules, indicate that the excess calcium of the granule fractions relative to the mitochondrial fractions is maintained within the particles of that fraction. The functional significance of the relatively large amount of calcium in chromaffin granules is not clear.

The presence of 150 mM sodium chloride or potassium chloride decreases calcium binding by granule or mitochondrial fragments incubated in 2.2 mM calcium chloride in 0.2 M Tris, pH 7, by about 50%. EDTA, 10−3 M, removes all but a small residual of the calcium associated with the granule or mitochondrial fragments whereas lowering the concentration of Tris increases calcium binding to about the same extent in both these subcellular fractions. The calcium‐binding properties of granule and mitochondrial fragments therefore appear to be quantitatively and qualitatively similar. Inhibition of catecholamine release by relatively high concentrations of sodium may be explained by competitive inhibition of calcium binding. Calcium binding by granule fragments decreases with an increase in hydrogen ion concentration.
The relation of karyotypic change to loss of contact inhibition of division in human diploid cells after SV40 infection
Authors: Weinstein David , Moorhead Paul S.
Published: February 2005

Following in vitro infection of human cell cultures with simian virus 40, karyotypic analyses were performed on the earliest serial culture in which cells were released from contact inhibition of division. In these cultures of diploid fibroblast‐like cells, normal karyotypes were found in excess of the statistical expectation for the number of background dividing cells. Thus, loss of contact inhibition of cell division occurs prior to the alteration of chromosome morphology. These events are two of the prime alterations in the series of steps comprising transformation by this virus. The chromosomal changes which were present represent the first cytological alteration detectable. Their distribution in the human karyotype was examined, but was found to have no relation to any specific chromosome or chromosome group.
Properties of mitotic cells prepared by mechanically shaking monolayer cultures of chinese hamster cells
Authors: Tobey R. A. , Anderson E. C. , Petersen D. F.
Published: February 2005

A technique has been developed for the selective detachment of mitotic cells from monolayer cultures of Chiness hamster cells with a simple reciprocating shaking machine. Cultures prepared by the shake treatment and placed in spinner flasks are routinely obtained, in which the mitotic fraction drops from 0.95–0.05 in 19 minutes. Some properties of mitotic cells prepared by this technique are described, along with a simple procedure for producing large quantities of mitotic cells. Cells chilled immediately after collection from a series of shake treatments complete mitosis synchronously upon subsequent resuspension in warm medium.
The incorporation of microinjected 14C‐amino acids into TCA insoluble fractions of the giant axon of the squid
Authors: Fischer S. , Litvak S.
Published: February 2005

Giant squid axons were microinjected with serine, valine and leucine‐C14 under controlled electrophysiological conditions. These amino acids are incorporated into TCA insoluble fraction in the isolated axon.

This incorporation is higher in the stimulated axons as compared to non‐stimulated ones. By processing separately the axoplasm and axon sheath, it was found that the last one is responsible almost entirely for the observed incorporation.

Through differential centrifugation of homogenates of microinjected axons was shown that the highest incorporation occurred in the 1500 × g sediment, which probably corresponds to membranes.

The incorporation of amino acids in stimulated axons, is strongly inhibited by chloramphenicol and actinomycin D.
Electrophysiological studies of the isolated posterior moiety of the electroplax of the electric eel
Authors: Webb George D.
Published: February 2005

Intracellular microelectrodes were used to measure resting and action potentials of electric eel electroplax cells from which the middle portion of the anterior moiety had been removed. External electrode studies of this preparation have been described by Chagas and Esquibel (C. R. Acad. Sc., Paris, 260: 3172 ('65)). In the present studies it was found that the resting and action potentials were almost as large as normal in the intact portion of the preparation, whereas these potentials were greatly reduced in the areas from which the anterior moiety had been removed. The reduction in amplitude was greater the farther the microelectrode was from the intact portion, indicating the possibility of decremental spread from the intact portions. The action potentials measured with external electrodes appeared to be an average of potentials from the various areas of the preparation. In other experiments the entire anterior moiety of the electroplax was removed, leaving only the innervated plasma membrane plus some adhering cytoplasm and extracellular material. Various high K+ solutions were used to bathe the inner surface. No action potentials could be elicited from these preparations, but resting potentials as high as 51 mV were observed using external electrodes. The resting potential could be reduced reversibly by carbamylcholine applied to the outer surface. Carbamylcholine applied to the inner surface had no effect.
A change in growth potential of cells after conversion by Rous sarcoma virus
Authors: Bader John P.
Published: February 2005

Chick embryo cells transformed by Rous sarcoma virus (RSV) were able to grow in suspension, either as colonies when trapped in nutrient agar, or in spinner cultures using liquid medium. Two strains of RSV, RSV (RAV‐1) and Schmidt‐Ruppin RSV, were able to increase the ability of chick embryo cells to grow in suspension but Rous‐associated virus (RAV‐1) and polyoma virus were not. Cells growing in suspension supported high levels of RSV production and a simple method for propagating large amounts of virus is suggested. Suspended noninfected cells, which do not grow extensively, lose their ability to be infected by RSV, suggesting that cellular divisions must be in progress for successful infection by RSV.
The need for direct cell contact in “contact” inhibition of cell division in culture
Authors: Schutz Leonard , Mora Peter T.
Published: February 2005

Non‐dividing mouse embryo fibroblasts which grew to a confluent cell density on one side of an ultra‐thin filter did not inhibit the active multiplication of the same type of cells growing at low cell density on the other side of the filter directly opposite the confluent side. The close proximity of the cells across the filter was not sufficient to cause inhibition of cell division. The phenomenon of “contact” or “density dependent” inhibition of cell division is therefore probably not mediated by a cellular product which remains concentrated near the cell surface.

The degree of contact inhibition of cell division was correlated with the local cell density on the same side of the filter. This relationship was found to be influenced strongly by the surface on which the cells were growing.
Growth of mouse fibroblasts in the presence of irradiated and lyophilized monolayers of the same type of cells
Authors: Schutz Leonard , Mora Peter T.
Published: February 2005

Certain cells, such as 3T3 mouse embryo fibroblasts, are inhibited from dividing when they grow to a characteristic cell density on a surface in tissue culture. We asked whether the inhibition of cell division could be attributed to the inert chemical composition of neighboring cells, that is, whether the residues of lyophilized cells retained the ability to inhibit the division of normal cells. In addition, we wanted to know whether cells in which DNA synthesis was imparied by irradiation would retain the capacity to effectively inhibit normal cells.

To answer these questions, confluent and non‐confluent layers of 3T3 cells were prepared in tissue culture dishes and the cells were either lyophilized or irrariated in situ. Fresh 3T3 cells were then added to these prepared layers and their growth was followed using radioactive label. There was no growth of added cells on the confluent monolayers of either untreated or irradiated cells. Growth was unimpeded on the monolayers of lyophilized cells. When cells were added to non‐confluent cultures of either normal or irradiated cells the added cells grew until they had covered the remaining surface of the culture dish and had come into contact with the pre‐existing cells. In the discussion, consideration is given to the role of available surface over which the cells can spread as well as to the possible interactions between neighboring cells.
Potentiation of bone marrow colony growth in vitro by the addition of lymphoid or bone marrow cells
Authors: Metcalf Donald
Published: February 2005

Colony formation and growth in vitro by C57B1 mouse bone marrow cells were analysed following stimulation by a standard dose of serum colony stimulating factor. Under restricted conditions, colony crowding was observed to potentiate colony growth rates. The addition of thymic or lymph node lymphoid cells or nonviable bone marrow cells also potentiated colony growth. Extensive reutilisation of nuclear material by bone marrow colony cells was observed when labeled lymphoid and bone marrow cells were added to the culture system. The results provide evidence that lymphocytes can exert trephocytic effects on proliferating hematopoietic cells.
Myogenesis of striated muscle in vitro: Hormone and serum requirements for the development of glycogen synthetase in myotubes
Authors: De La Haba Gabriel , Cooper George W. , Elting Virginia
Published: February 2005

The fusion in vitro of embryonic myoblasts to form multinucleated myotubes requires the addition of serum to a basal nutrient medium. The serum requirement for fusion can be satisfied by insulin with somatotropin potentiating its effect. Myotubes formed under these conditions fail to differentiate to cross‐striated, spontaneously contractile muscle fibers. This arrest of development is reversible if serum is restored to the medium.

Development of the enzyme glycogen synthetase was studied as an additional indicator of muscle differentiation. In cultures developing in the presence of serum, this enzyme was demonstrated by autoradiography to be highly concentrated in myotubes as compared to mononuclear cells. The activity of the enzyme remains low in (1) cultures formed in response to insulin and somatotropin in the absence of serum, as well as (2) in cultures formed in unsupplemented basal medium which are virtually lacking in myotubes. The addition of serum to (1) restores the development of this enzyme. Serum which has been extensively digested with the proteolytic preparation, pronase, and subjected to boiling temperature, when combined with insulin and somatotropin is also capable of promoting the development of glycogen synthetase to a specific activity which exceeds the control. The serum factor is not lost on exhaustive dialysis, nor can enzyme promoting activity be liberated by heat denaturation of serum proteins.
Regulation of melanin synthesis in mammalian cells, as studied by somatic hybridization. I. Evidence for negative control
Authors: Davidson Richard , Ephrussi Boris , Yamamoto Kohtaro
Published: February 2005

Somatic hybrids between pigmented Syrian hamster cells and unpigmented mouse cells were isolated and propagated in vitro. These hybrids are unpigmented and lack dopa oxidase (and tyrosinase) activity, which is correlated with the pigmentation of the Syrian hamster cells. In contrast, the presence of three other enzymes (LDH, MDH, and thymidine kinase) also specified by the hamster genome but unrelated to pigment synthesis is observed in the hybrid cells. This suggests that the repression of dopa oxidase in these cells is a specific effect on the enzyme associated with the differentiated state of pigment cells. It is concluded that the genetic control of differentiation in this case involves a diffusible regulator substance which functions negatively.
Persistent synthesis of 5S RNA when production of 28S and 18S ribosomal RNA is inhibited by low doses of actinomycin D
Authors: Perry Robert P. , Kelley Dawn E.
Published: February 2005

To determine whether transcription of the genes coding for 5S ribosomal RNA depends upon the concurrent activity of the genes for 28S and 18S ribosomal RNA we studied the synthesis of 5S RNA in cultured L cells when the synthesis of the 45S precursor of 28 and 18S RNA was inhibited with low doses of actinomycin D. Synthesis of 5S RNA was measured by following the incorporation of 3H uridine into components which, upon acrylamide gel electrophoresis, co‐migrated with markers of 5S RNA obtained from 32P labeled ribosomes. We observed that the synthesis of 5S RNA persists in the absence of detectable 28S and 18S RNA synthesis, continuing at the normal rate for several hours and at a reduced rate for at least a generation time. This strongly supports the concept that 45S RNA is not a precursor of 5S RNA, and indicates furthermore that neither the 45S component, nor any of the intermediates involved in its transition to 28S and 18S RNA, are involved in controlling the output of the 5S genes The 5S RNA which is made during actinomycin treatment is retained predominantly in the nucleoplasm and undergoes a turnover of about 3.5% per hour. It apparently cannot be utilized when ribosome synthesis resumes following removal of the actinomycin.
The retinal rod outer segment of the frog: Detachment, isolation, phosphorus fractions and enzyme activity
Authors: Lolley Richard N. , Hess Helen H.
Published: February 2005

Frog retinal rod outer segments were detached from dark adapted retinas by (1) agitation in frog Ringer's solution or (2) by crushing between two glass surfaces. The resulting suspensions were further purified by low and high speed centrifugation procedures in Ficoll density gradients. The density of the outer segments in Ficoll solutions was found to be 1.09. The large frog outer segments, unlike bovine outer segments, are not readily separated from nuclei, which were estimated to comprise 2.6–8% of the material, based on DNA analyses. The RNA/DNA ratio was 0.4–0.5, like that of neuronal nuclei. Representative enzymes of glycolysis (lactic dehydrogenase and glyceraldehyde phosphate dehydrogenase), phosphogluconate oxidation (glucose‐6‐phosphate dehydrogenase and 6‐phosphogluconate dehydrogenase), the citric acid cycle (malic dehydrogenase) and ATP degradation (ATPase) were assayed. A major part of the malic dehydrogenase activity was probably due to inner segments attached to some of the outer segments. Glyceraldehyde phosphate dehydrogenase and glucose‐6‐phosphate dehydrogenase (but not lactic dehydrogenase) activities were lower in detached outer segments purified on Ficoll gradients than in samples of outer segment layer microdissected from freeze‐dried sections of frog retina, as well as in whole retina. The data suggest that the activities of all the enzymes studied are intrinsically low in rod outer segments.
Separation of cells by velocity sedimentation
Authors: Miller Richard G. , Phillips R. A.
Published: February 2005

A system for fractionating populations of living cells by velocity sedimentation in the earth's gravitational field is described. The cells start in a thin band near the top of a shallow gradient of 3% to 30% fetal calf serum in phosphate buffered saline at 4°C. Cell separation takes place primarily on the basis of size and is approximately independent of cell shape. A sharply‐defined upper limit, called the streaming limit, exists for the cell concentration in the starting band beyond which useful cell separations cannot be achieved. This limit, which varies with the type of cell being sedimented, can be significantly increased by proper choice of gradient shape. For sheep erythrocytes (sedimentation velocity of 1.6 mm/hour) it is 1.5 × 107 cells/ml. Measured and calculated sedimentation velocities for sheep erythrocytes are shown to be in agreement. The technique is applied to a suspension of mouse spleen cells and it is shown, using an electronic cell counter and pulse height analyzer, that cells are fractionated according to size across the gradient such that the sedimentation velocity (in mm/hour) approximately equals r2/4 where r is the cell radius in microns. Since cells of differing function also often differ in size, the system appears to have useful biological applications.
The calcium‐mediated promotion of mitotic activity in rat thymocyte populations by growth hormone, neurohormones, parathyroid hormone and prolactin
Authors: Whitfield J. F. , Perris A. D. , Youdale T.
Published: February 2005

Growth hormone, oxytocin, parathyroid hormone, prolactin and lysine vasopressin strongly stimulate mitotic activity in rat thymocyte populations maintained in vitro. These hormones have no mitotic effect on cells maintained in calcium‐free medium. It is concluded that they stimulate mitosis only indirectly by sensitising the mitotically competent segment of a thymocyte population to the action of calcium. The stimulatory action of calcium itself is opposed by low concentrations of the mucopolysaccharide chondroitin sulphate. However, the inhibitory action of chondroitin sulphate can be overcome by growth hormone.

A possible common mechanism of action of these hormones on mitotically competent cells is discussed.
Evidence from studies of birefringence of structure across the dimple region of red cells
Authors: Shrivastav B. B. , Burton A. C.
Published: February 2005

Analysis of the equilibrium of the normal biconcave human red cell, in terms of its tension and a pressure inside, suggests a force of attraction between the opposite membranes at the dimple regions. The analogous attraction that causes rouleaux formation is mediated by long‐chain molecules. Single cells hanging on edge between polarizer and analyser, almost “crossed,” were photographed at different angles to the axis of the polarizer. Enlarged prints were scanned by a photometer. For single cells the records showed non‐significant fluctuations of intensity, but mean values for 32 cells showed a very significant sinusoidal variation with angle, as predicted by theory for birefringence in the cell at the dimple region. For the rim region, the averaged data showed no variation with angle. In cells moderately osmotically swollen, birefringence in the centre of the dimple region was absent, but persisted close to the inside of the membranes. The latter disappeared in cells further swollen to a biconvex shape. The data is interpreted as indicating oriented chains of molecules across the interior of the cell at the dimple region. The behaviour on swelling was what had been seen in a model with nylon fibres oriented between the charged plates of a condenser, in which the variation of attractive force with distance was adequate to explain the equilibrium of the red cell membrane.
Incorporation of H3‐uridine and the isolation and characterization of RNA from squid axon
Authors: Fischer S. , Gariglio P. , Tarifeño E.
Published: February 2005

H3‐Uridine microinjected in the giant axons of the squid is incorporated in a TCA insoluble material. There is no difference between stimulated and resting axons as to the amount incorporated.

The amount incorporated is increased if the stimulation precedes the microinjection of the tracer.

RNA was purified and characterized from the axoplasm, axon sheaths and from a purified membrane preparation obtained from squid retinal nerve.
Early alterations in amino acid pools and protein synthesis of diploid fibroblasts stimulated to synthesize DNA by addition of serum
Authors: Wiebel F. , Baserga R.
Published: February 2005

Diploid human fibroblasts in culture (WI 38) were allowed to reach a stationary phase and were then stimulated to reenter DNA synthesis and cell division by addition of serum to the culture medium. The rate of protein synthesis increased during the first hours after addition of serum reaching at three hours a plateau value that continued for at least 24 hours after serum addition. Inhibition of protein synthesis during the early hours after serum addition abolished the stimulation of DNA synthesis occurring 20 to 28 hours later.

Increased protein synthesis was preceded by a rapid decrease in the intracellular pool size of most amino acids. These changes were independent of concomitant protein synthesis. They suggest that serum exerts an immediate effect on the function of the cell membrane.
Differentiation of a cell line of myeloid leukemia
Authors: Ichikawa Yasuo
Published: February 2005

A cell line was established in vitro from a spontaneous myeloid leukemia of SL strain mice. This cell line was cytologically identified as myeloblast, and its normal differentiation appeared to be completely blocked in mass culture. When the line cells were seeded in soft agar with a conditioned medium from normal cells, either macrophages or neutrophil granulocytes appeared from a single clone. The rate of formation of colonies containing differentiated cells always increased with an increase in the concentration of conditioned medium. The conditioned medium from this line cell was not as effective as was that from normal cells in inducing differentiation.
Migration and proliferation of diploid human fibroblasts following “wounding” of confluent monolayers
Authors: Raff E. C. , Houck J. C.
Published: February 2005

Six diploid human fibroblast strains were grown in confluent monolayers. Holes were scraped in these monolayers and the number of cells proliferating into these “wounds” with time were determined. The migration and mitotic aspects of the proliferation of fibroblasts into these wounds were analyzed separately.

Small amounts of undialysed or dialysed serum were essential for cell division but not migration. Saline extracts of skin could not substitute for serum in the medium. Neither zinc nor cupric ion at tolerable concentrations (10−5M) increased the rate of cell proliferation.

Normal human fibroblasts did not immediately start to divide from confluency into the “wound” space. Their generation time was about 32–39 hours. Fibroblasts from patients with cystic fibrosis began to divide almost immediately into the “wounded” area. Their generation time was about 48 to 56 hours.
Photolysis in a culture medium for Tetrahymena pyriformis
Authors: Lee Donald
Published: February 2005

Considerable variability has been found in the yield of cells in batch cultures of Tetrahymena pyriformis grown axenically in 1% tryptone/0.05% yeast extract. This variability has been traced to the photolysis by visible light of the flavin mononucleotide and thiamine components of yeast extract.
Density dependent inhibition of cell growth in cultures of primary and established lines of cells
Authors: Oren Rachel , Kohn Alexander
Published: February 2005

The effect of cell crowding on DNA synthesis (incorporation of 3HTdR and 32PO4) was studied by an improved method in monolayers of secondary cells and established cell lines, either normal or transformed by viruses or carcinogens. The method was based mainly on pulse labeling of cultures of cells a few hours after their seeding in equal numbers onto areas of different size in identical dishes, a condition which ensured equal physiological conditions and different degrees of crowding of cells.

DNA synthesis was hardly inhibited in crowded monolayers of secondary chick, mouse and hamster embryo cells. The incorporation of radioactive thymidine and phosphate into DNA of cell lines such as BHK 21, 3T3/SV40 and L929 was strongly inhibited. An SV40‐transformed line of hamster kidney cells (HKT7) synthetized DNA equally well in sparse as in crowded monolayers. In lines of human amnion (FL) and BHK 21 cells which were more extensively studied the degree of inhibition of DNA synthesis was inversely proportional to their density.

Autoradiography after 3HTdR pulse‐labeling indicated that the same proportion of cell nuclei were labeled in sparse and in crowded cultures. The extent of labeling (number of grains per nucleus) was lower in crowded cultures of those cells that also showed inhibition of incorporation of this label as measured by scintillation. The inhibition is thus expressed in retardation of DNA synthesis in cells in S phase rather than arresting it in a larger percentage of cells.
Divalent cation activation of flagellar ATP‐phosphohydrolase from bull sperm
Authors: Young L. G. , Nelson L.
Published: February 2005

The apparently inconsistent reports on flagellar ATPase properties may be resolved by elimination of adenylate kinase from the system. Removal of the adenylate kinase from alkaline M/2 KCl extracts of bull sperm flagella yields a spermosin‐ATPase which liberates only the terminal phosphate of ATP. In any case spermosin is preferentially activated by calcium. However, combination of spermosin with flactin (e.g., by addition of digitonin and MgCl2 to the extraction medium) produces an ATPase much more highly activated by magnesium. But flactospermosin has so far resisted purification from its adenylate kinase contaminant. In divalent cation activation, pH optima and nature of ATP hydrolysis, the flagellar contractile protein system closely parallels the muscle system.
Contraction of protoplasm. III. Cinematographic analysis of the contraction of some heterotrichs
Authors: Jones Alick R. , Jahn Theodore L. , Fonseca James R.
Published: February 2005

The contraction of Stentor and Blepharisma, in response to mechanical and electrical stimulation and of Spirostomum in response to mechanical stimulation is described. All three species respond to electrical stimulation by contraction of the cytoplasm, beginning at the anodal end regardless of orientation of the animal. The differences in contractile ability and shapes during contraction are discussed in relation to body form and microanatomy. Stentor and Spirostomum also respond to mechanical stimulation. Dropping a weight on the slide causes contraction of the whole body of Spirostomum, but not of Stentor. Stimulation of the oral region of Stentor by means of a vibrating needle causes a contraction of the entire body, but this sensitivity is limited to the oral region. Blepharisma does not respond to mechanical stimulation. Spirostomum and Stentor undergo rapid spontaneous contractions, but Blepharisma does not contract spontaneously.
Contraction of protoplasm. IV. Cinematographic analysis of the contraction of some peritrichs
Authors: Jones Alick R. , Jahn Theodore L. , Fonseca James R.
Published: February 2005

The contraction and relaxation of Vorticella difficilis, V. campanula and Carchesium sp. were studied by high speed cinematography. In Vorticella it was shown that coiling of the stalk usually started near the zooid and spread downwards; the point of initiation bore no relation to the position of the stimulating electrodes. Contraction took about 5 msec to complete, and the fully contracted animals were 29 ± 3.9% of their original lengths. The zooids were 66 ± 5.0% and the stalks 14 ± 6.0% of their original lengths (V. difficilis). The shortening of the stalk was mostly in the form of coiling. Measurement of the myoneme length demonstrated that its real shortening was less than 10%. Thus the contraction is virtually isometric, producing a helical deformation of the stalk. As the stalk contracts it takes the form of a steeply pitched helix. This change in shape should produce rotational forces on the zooid (torque). Physical models of similar proportions produced about 1.5 revolutions of torque for similar changes in pitch. However during contraction no turning of the zooid was detected, though rotation did occur after the completion of contraction.

In Carchesium the contraction is not so isometric, the myoneme apparently shortening by 20%. While the coiled shape of the contracted Vorticella stalk can be explained by its acentric structures, the stalk of Carchesium is much more symmetrical in cross‐section, demonstrating that a high acentricity is not necessary for helical coiling. In all three species there seems to be some separation of the control of zooid and stalk contraction.
Enzyme kinetics in mammalian cells. II. Simultaneous determination of rate constants for the first three steps of galactose metabolism in red cells
Authors: Hill Helene Z. , Puck Theodore T.
Published: February 2005

The method for simultaneous measurement of the first two sequential enzymes of galactose metabolism of red cells has been extended to include the third step of the chain, epimerization of uridine diphosphogalactose to uridine diphosphoglucose. The method is rapid and precise and is applicable to a variety of genetic‐biochemical problems.
An improved chemically defined culture medium for strain L mouse cells based on growth responses to graded levels of nutrients including iron and zinc ions
Authors: Higuchi Kiyoshi
Published: February 2005

Nutritional factors were evaluated for effects on growth of mouse fibroblast cells in suspension in a chemically defined medium. Quantitative requirements for each of the essential amino acids, choline, inorganic phosphate, iron, and zinc were established. An improved chemically defined medium was formulated on the basis of the findings yielding populations of L cells in excess of 5 × 106 per ml without nutrient replenishment. When spent medium was replaced periodically, yields approaching 30 × 106 cells per ml were attained. The efficiency of utilization of most amino acids in the new medium appears to be 2‐ to 3‐fold better than results reported by others.
Nitrogen metabolism during synchronous growth of chlorella. II. Free‐, peptide‐, and protein‐amino acid distribution
Authors: Hare Theodore A. , Schmidt Robert R.
Published: February 2005

The levels of free‐, peptide‐, and protein‐amino acids were measured during the synchronous growth and division cycle of a thermophilic strain of Chlorella pyrenoidosa. Most of the protein amino acids exhibited little periodism (as % of total cellular‐N); however, the free‐ and peptide‐amino acids showed a variety of dramatic changes in level during the cell cycle.

Fractionation of the acid‐soluble peptides by Sephadex gel‐filtration showed that an average of only 2.8% of the peptide amino acids were associated with peptides of high molecular weight (> 5000), while approximately 75% of the peptide amino acids were components of low molecular weight peptides (< 700). The low molecular weight peptides were predominately made up of relatively few amino acids (i.e., alanine, glutamate, lysine, glycine and arginine accounted for approximately 92% of the low molecular weight peptide amino acids).

Several experiments revealed that nucleotide‐peptides do not contribute significantly to the pool of acid‐soluble peptides during the cell cycle of this organism.
Tracer kinetic analysis of incorporation of glucose and adenine by yeast cells
Authors: Burns Victor W. F.
Published: February 2005

A kinetic model of adenine and glucose incorporation into log phase yeast cells has been developed, and experimental tests of certain predictions of the model validate it. The cellular pool of purine nucleotides is 6 × 10−3 μmoles per 107 cells, the turnover time of this pool is 21.8 minutes, and the rate of incorporation into nucleic acids is 4.86 × 10−2 μmoles per hour per 107 cells. Corresponding figures for glucose are given. The model should be useful in other kinetic studies and the method of applying it is explained.
Characterization of RNA molecules restricted to the nucleus in mouse L‐cells
Authors: Shearer Ruth W. , McCarthy Brian J.
Published: February 2005

RNA molecules which are restricted to the nucleus in mouse L‐cells were characterized by the technique of RNA/DNA hybridization. Competition of cytoplasmic RNA with labeled nuclear RNA of various sizes revealed that the RNA restricted to the cell nucleus is heterogeneous in size. Competition for sites on fractions of mouse DNA of various base compositions indicated that this unstable RNA is also heterogeneous in base composition. Fractionation of nuclei into three subfractions failed to separate the uniquely nuclear RNA from the precursors of cytoplasmic RNA. The significance of the selective transport of RNA from the nucleus to the cytoplasm and its importance in the control of gene activity in eucaryotic cells is discussed.
Density distribution analysis of In vivo and In vitro colony forming cells in bone marrow
Authors: Haskill J. S. , McNeill T. A. , Moore M. A. S.
Published: February 2005

The technique of buoyant density separation in gradients of Bovine Serum Albumin has been used to separate hemopoietic cell populations in mouse bone marrow that form in vivo spleen colonies and in vitro colonies of granulocytes and macrophages in an agar culture system. The density distribution profiles showed a number of reproducible density subpopulations of both in vivo and in vitro colony forming cells (C.F.C.'s). The mean density of in vitro C.F.C.'s exceeded that of the in vivo but overlap of the density profiles of the two populations was evident. Density‐related differences in seeding efficiency of in vivo C.F.C.'s were observed.

Freund's adjuvant treatment increased marrow and spleen in vitro C.F.C. populations. Marrow density profiles obtained three and seven days after adjuvant showed a progressive increase in in vitro C.F.C.'s in a restricted density region with no associated elevation of in vivo activity.

The antimitotic agent, vinblastine, revealed differences in mitotic activity between the two cell populations, reducing the in vitro C.F.C. population to .07% and the in vivo to 5% of normal in 24 hours. Density separation of vinblastine‐treated marrow produced density regions devoid of in vitro activity but containing in vivo in vivo C.F.C.'s which, upon transfer to irradiated recipients, regenerated both in vivo and in vitro density distribution profiles.