bluuebunny/crossref_metadata_2025 huggingface dataset:
An inhibitor of protein synthesis in cytoplasmic extracts of density inhibited cells
Authors: Engelhardt Dean L.
Published: February 2005

Cytoplasmic extracts of green monkey kidney‐Vero M3 cells that have been grown to high cell density and have entered the stationary phase of growth lose the capacity to synthesize proteins after they have been frozen and thawed. The same loss of protein synthetic capacity is not observed when cytoplasmic extracts of low cell density Vero M3 or HeLa S‐3 cells are frozen and thawed before assay, nor when high cell density Vero M3 cell extract is assayed without having been frozen. The loss of the protein synthesis capacity of the frozen and thawed extracts of stationary phase Vero M3 cells is accounted for by the appearance of an inhibitor. The inhibitor is precipitated in the 30 to 70% ammonium sulfate fraction of the 100,000 g supernatant. It is inactivated by heat and is non‐dialyzable. It blocks the transfer of amino acids from tRNA to growing peptide chains.

The amount of this inhibitor in the extract (measured by relative inhibition of in vitro protein synthesis) increases as a function of the density of the cells from which the extract was made, and the increase can be correlated with the progressive turnoff of protein synthesis in whole cells.
Susceptibility to polycythemia of hemopoietic spleen colonies produced by cultured embryonal liver cells
Authors: Latsinik Natalia V. , Samoylina Nina L. , Chertkov J. L.
Published: February 2005

The survival of colony‐forming cells in organ cultures of the mouse embryonal liver was studied. During cultivation colony‐forming cells acquire the type of regulation characteristic of the adult organism. Factors affecting the change in the type of regulation from embryonal to adult of the hemopoietic stem cells in cultures are discussed.
The kinetics of resensitization of Tetrahymena following recovery from effects of cycloheximide
Authors: Heyer Carolyn B. , Frankel Joseph
Published: February 2005

Synchronized cells of Tetrahymena pyriformis strain GL‐C were exposed to cycloheximide (CHI) (0.2 μg per ml) from 40 to 140 minutes after the end of the heat synchronizing treatment. Recovery takes place during this treatment (Frankel, 1970). The CHI was washed out at 140 minutes. At various times after washout dividing cells were isolated in micro‐drops under oil, and one daughter was transferred to a test drop containing CHI (0.2 μ per ml). The generation time of both daughters was recorded, and the “percent prolongation” of generation time brought about by the test exposure of one cell to CHI was computed for each cell‐pair. This procedure was carried out for groups of cell‐pairs at different times after the end of the CHI pretreatment. Comparable tests were performed with two control series, one which had not previously been exposed to CHI and another for which CHI was present continuously. Comparison of the prolongation observed in control and experimental series demonstrated that cells which have earlier undergone recovery in CHI gradually become resensitized following washout of the drug. Cells progressively lose most of their original resistance in a period of somewhat over three cell generations; however, a small but significant fraction of this resistance is still retained seven to eight generations after the CHI pretreatment.
Coordination of ribosomal RNA synthesis in vertebrate cells
Authors: Hill Richard N. , McConkey Edwin H.
Published: February 2005

Xenopus embryo cells and HeLa cells were investigated under various conditions to test for coordinate synthesis of high molecular weight (28S and 18S) and low molecular weight (5S) rRNA. Xenopus embryos initiate 28S and 18S rRNA synthesis at gastrulation (Brown and Littna, '64); we found that 5S rRNA synthesis is coordinately initiated with the 28S and 18S rRNAs at the same time in development. Dissociated Xenopus blastula cells were cultured in vitro for several hours to condition the medium; post‐gastrula cells were then grown in the conditioned medium to test for the existence of an inhibitor of rRNA synthesis. No inhibitor was detected.

Low doses of actinomycin D profoundly inhibit the synthesis of 28S and 18S rRNA in HeLa cells, while 5S rRNA synthesis is less affected by this treatment. Therefore, actinomycin D does not produce a coordinate inhibition of all rRNA species. Similar effects of the antibiotic were found in cultured amphibian cells. Synchronized HeLa cells reinitiating RNA synthesis following mitosis also respond to actinomycin D in a non‐coordinate manner.
The release of membrane‐bound calcium by radiation and sulfhydryl reagents
Authors: Tolberg Adelaide B. , Macey Robert I.
Published: February 2005

Effects of ionizing radiation and of sulfhydryl reagents on the 45Ca binding of red cell membranes were studied. Corresponding effects of these agents on potassium leak from intact red cells were also determined. Essentially all the 45Ca associated with the ghosts appeared to be bound. Calcium binding could be described by assuming two independent groups of binding sites with dissociation constants of about 6 × 10−4 m and 2 × 10−4 m. The total binding capacity was about 2.5 × 10−4 moles/g ghost protein. Membrane calcium was decreased by radiation and by the two sulfhydryl reagents, p‐chloromercuribenzoate (PCMB) and N‐ethyl maleimide (NEM). The tightly bound calcium fraction appeared to be most affected by these agents. Changes in potassium leak evoked by varying doses of agents appeared to parallel effects on membrane calcium. These investigations suggest that the increased cation permeability observed after exposure or red cells to radiation or sulfhydryl reagents may be related to alterations in the calcium‐binding properties of the cell membrane.
Lipid components of sarcotubular membranes
Authors: Sanslone W. R. , Bertrand H. A. , Yu B. P. , Masoro E. J.
Published: February 2005

The lipid composition of a highly purified preparation of rat skeletal muscle sarcoplasmic reticulum was studied. These membranes contain per mg of protein 0.50 ± 0.02 μmoles of phosphatidylcholine, 0.13 ± 0.02 μmoles of phosphatidylethanolamine and 0.07 ± 0.02 μmoles ofphosphatidylinositol. These three components account for 97.3% of total lipid phosphorus. Unlike other mammalian membranes so far studied, this preparation contains neither sphingomyelin nor phosphatidylserine. Neural lipids were also measured and it is concluded that neither cholesterol nor other neutral lipids are components of the membranes studied. The results of this study indicate therefore that the lipid profile of sarcotubular membranes is relatively simple compared with most other membranes.
Lanthanum‐Induced alterations in cellular electrolytes and membrane potential in ehrlich ascites tumor cells
Authors: Levinson Charles , Mikiten Terry M. , Smith Thomas C.
Published: February 2005

We have investigated the effect of varying La+3 concentrations (0.01 mM to 2.0 mM) on membrane potential and electrolyte composition of Ehrlich ascites tumor cells. La+3 concentrations less than 0.02 mM had no effect. Above 0.02 mM, La+3 induced concentration‐dependent loss of electrolytes and water from the cells. At 1.0 mM the effect was maximal and resulted in an 87% reduction in cellular K+, 79% in Cl− and 21% in Na+ within 4.8 minutes. The Na+ loss occurred even in the face of an electrochemical potential gradient favoring Na+ entry. La+3 increased the recorded values of membrane potential; the magnitude of the effect was related to the external La+3 concentration, and was maximal at 1.0 mM. Studies using 140La showed that La+3 binds rapidly to the cell surface and does not enter the cells. The amount of La+3 bound to the cells was related to the external La+3 concentration by a sigmoidal curve and was maximal at about 1.0 mM. The bound La+3 could not be displaced by either added La+3 or Ca+2. Agents known to effect the integrity of the cell membrane, such as phospholipase C, neuraminidase, pronase and Hg+2 were tested for their ability to displace bound La+3. Only pronase displaced bound La+3, indicating that La+3 associates with cell protein. It is hypothesized that La+3 rapidly interacts with membrane protein causing alterations in membrane permeability and capacity to actively transport ions.
Hemopoietic inductive environment necessary for an early stage in differentiation of thymic immune cells: Effect of antilymphocytic serum
Authors: Bennett Michael
Published: February 2005

Treatment of adult mice with rabbit anti‐mouse thymocyte serum decreased the number and frequency of alloantigen‐sensitive units responsible for graft‐versus‐host reactions and prolonged the survival of skin allografts. Whereas alloantigen‐sensitive units were suppressed directly in vitro, they were not apparently suppressed directly in vivo since the fall‐off of their numbers and/or function did not occur during the first day after serum injection. Treatment of prospective recipients of thymus cell grafts impaired the production of alloantigen‐sensitive units by transplanted primitive progenitors. Differentiation with proliferation of alloantigen‐sensitive units was less affected.

Similarly, treatment of prospective recipients of thymus cell grafts with antilymphocytic serum impaired the production of specific inducer cells responsive to sheep erythrocytes by transplanted more primitive cells, presumably antigenreactive cells. Production of new precursors of anti‐sheep erythrocyte hemolytic plaque‐forming cells by transplanted bone marrow was not affected. Thus, antilymphocytic serum impairs the generation of immunocompetent cells of thymic origin by altering a hemopoietic inductive environment necessary for an early stage in differentiation.
Effects of anthramycin and actinomycin on RNA synthesis patterns in L1210 cells
Authors: Kann Herbert E. , Kohn Kurt W.
Published: February 2005

Anthramycin and actinomycin D, two different types of DNA‐binding antibiotics, were compared for their effects on RNA synthesis in suspension cultures of mouse leukemia L1210 cells. RNA was labeled with radioactive uridine and selective effects on the synthesis of different classes of RNA were studied by sucrose gradient sedimentation of RNA purified from whole cells or from nucleolar and nucleoplasmic fractions.

Two major differences were noted. (1) Whereas actinomycin produced two phases in the inhibition of uridine incorporation, the rapid phase being complete within a few minutes, anthramycin produced only a slow progressive inhibition. (2) Whereas actinomycin selectively inhibits nucleolar 45s RNA synthesis, anthramycin inhibits this RNA equally to the inhibition of the same size RNA in the nucleoplasm.

Both antibiotics caused a shift towards lower molecular weight (slower sedimentation) in the distribution of nucleoplasmic RNA molecules synthesized in the presence of drug. When the two antibiotics were compared at concentrations producing equal extents of inhibition of nucleoplasmic RNA synthesis, anthryamycin produced the greater shift. The shift in sedimentation anthramycin produced the greater shift. The shift in sedimentation was not due to a slowing of RNA chain growth rate, since the change in sedimentation persisted when uridine incorporation time was increased so as to compensate for the reduction in RNA synthesis rate.

The selective inhibition of nucleolar RNA synthesis by actinomycin could be due to possible differences in the properties of the different RNA polymerases, or to differences in the initiation rates for transcription. The absence of selectivity in the case of anthramycin might be related to the near irreversibility of its binding to DNA. The shift towards lower molecular weight of the RNA synthesized is compatible with (but does not constitute strong evidence for) premature termination of RNA chains.
Density distribution and cation composition of red blood cells in newborn puppies
Authors: Lee Ping , Miles P. R.
Published: February 2005

The density distribution and cation composition of red blood cells from newborn puppies have been studied. The density distribution of red cells from a newborn puppy in a bovine serum albumin density gradient resembles a normal distribution with a peak density at a region less than that found for adult dog red cells. In two weeks the whole distribution shifts toward a more dense region, and a second cell peak appears so that the distribution becomes bimodal. This second cell peak is smaller than the original peak, and it appears at a region of lower density. In nine weeks the distribution becomes a normal one again, but the peak density corresponds to the peak density of the second cell peak which first appeared at two weeks. Evidence has been obtained to show that fetal red cells are located in the more dense cell peak and neonatal cells are in the less dense second peak. These results were obtained by labeling fetal cells with Cr51 and neonatal cells with Fe59. The analysis of the cation content of these cells shows that fetal cells contain more K and Na and have a higher K/Na ratio than adult red cells. Furthermore, neonatal cells contain considerably less cation and hemoglobin than do fetal cells. From a study of the cation and hemoglobin content of red cells appearing in various density fractions it is concluded that fetal cells lose K and Na during the first two weeks after birth. Thus, the change in the density disribution of the erythrocytes is thought to be due to two factors: (1) An increase in the density of fetal cells due to the loss of K and Na and, hence, water during the first two weeks after birth, and (2) the entry of less dense neonatal cells into the circulation.
Properties and cellular distribution of cyclic AMP‐dependent protein kinase from thymus
Authors: Klein Monroe I. , Makman Maynard H.
Published: February 2005

A protein kinase that catalyzes the phosphorylation of histone was partially purified from rat thymus, and the rate of histone phosphorylation was stimulated three‐ to fourfold by 1 × 10−6 M adenosine 3′,5′‐monophosphate (cyclic AMP). Thymic protein kinase was more active than the enzyme from spleen. Histone fractions f1, f2a, f2b, and f3 were all capable of serving as phosphate acceptors for the thymic protein kinase, and the rate of phosphorylation of each fraction was stimulated by cyclic AMP. The ability of various 3′,5′‐mononucleotides to stimulate protein kinase activity was compared. Inosine 3′,5′‐monophosphate (cyclic IMP) was the most effective substitute for cyclic AMP.

The cellular distribution of cyclic AMP‐dependent protein kinase and adenylate cyclase activities in the thymus was determined. Cyclic AMP‐dependent protein kinase activity is present in both small thymocytes and residual thymic tissue. The specific activity of protein kinase from residual tissue, both for basal and cyclic AMP‐stimulated enzyme, was greater than that of enzyme from small thymocytes. In contrast to this, adenylate cyclase activity is predominately localized in the thymocytes.
Fibrinogen inhibits red cell adhesion to glass
Authors: George James N.
Published: February 2005

Studies of human erythrocyte adhesion to glass have demonstrated consistently greater adhesion with serum‐containing media than with a comparable concentration of plasma. This serum‐plasma difference is explained by the adhesion‐inhibiting property of plasma fibrinogen. The fibrinogen effect is probably mediated through its firm binding to glass, since no adsorption onto the red cell surface could be demonstrated.

The ability of more red cells to adhere to a foreign surface after plasma coagulation (the formation of serum from plasma) may be significant in the red cell surface interactions necessary for the formation of a fibrin‐red cell thrombus.
The multiple hemoglobins of the chick embryo
Authors: Fraser Ronald , Horton Bennett , Dupourque Daniel , Chernoff Amoz
Published: February 2005

Two embryonic hemoglobins are found in chick erythrocytes during early development by column chromatography on DEAE‐cellulose and by electrophoresis on starch gel and gelatinized cellulose acetate. Beginning during the sixth day of incubation these are replaced by three different hemoglobins. Following hatching, chicks lose the most alkaline component, so that in the adult two hemoglobins are again found. Chromatographic fractionation on phosphonic acid cellulose also revealed an increase in the number of hemoglobins present in chicks during their development. We report the presence of at least 11 hemoglobins whose relative concentrations rise and fall during chick ontogeny. Failure to recognize the multiplicity of chicken hemoglobins is believed to be the major source of the confusion regarding this subject in the present literature.
Effect of X‐irradiation of one partner on hybrid frequency in fusions between Chinese hamster cells
Authors: Harris Morgan
Published: February 2005

Sublines derived from V79 and B150 Chinese hamster cells lack hypoxanthine‐guanine phosphoribosyltransferase (HGPRT) and thymidine kinase (TK) respectively. When these strains are cultivated together without virus treatment in HAT medium, hybrid colonies with normal enzymic patterns arise in high frequency. The ratio of proliferating hybrid colonies to the minority cell inoculum in mixed cultures is approximately 1/1000. This observation has been used to examine the effect of x‐irradiation pretreatment of one cell type on the frequency of hybrid formation in mixed cultures. B150 cells (TK‐) were irradiated in monolayer cultures at dose levels of 200–4000r (180 KV, 15 ma). After trypsinization, the irradiated cells were mixed with unirradiated V79 cells (subline 129, HGPRT‐) and cultivated in HAT medium. The per cent decline in hybrid frequency as a function of x‐irradiation was compared to the relative decline in viability of x‐irradiated B150 cells when assayed in cultures alone. These curves diverged markedly, with the frequency of proliferating hybrids decreasing much less rapidly with radiation dose than survival of B150 cells. By contrast, when B150 cells were subjected to acute heat shock for graded intervals and subsequently mixed with untreated V79–129 cells, both viability of B150 cells and hybrid formation declined at the same rate. Our results suggest that lethally irradiated cells can still fuse with normal cells, and may contribute functional chromosomes to the hybrid karyotype. At limiting doses of x‐irradiation this technique may be useful as a means for induced segregation of marker chromosomes.
Lanthanum‐induced alterations of cellular electrolytes in Ehrlich ascites tumor cells: A new view
Authors: Levinson Charles , Smith Thomas C. , Mikiten Terry M.
Published: February 2005

We have shown previously that Ehrlich ascites tumor cells maintained at room temperature under an oxygen atmosphere lose Na+, K+ and Cl− isosmotically when exposed to La+++ (0.1 to 1.0 mM). Concomitant with these changes there is an increase in the recorded membrane potential (increasing intracellular negativity). The present studies further characterize the effect of La+++ on electrolyte distribution. Ehrlich ascites tumor cells were maintained at 0.5° C to permit Na+ gain and K+ loss. The addition of 1 mM La+++ to low temperature cells induces rapid loss of Na+, K+ and Cl−. This net loss of cellular electrolytes occurs even in cells depleted of ATP content using 2‐deoxyglucose (5 mM) and rotenone (10−6 M). Analysis of the appearance of tracer 22Na in the environment of cells preloaded with the radioisotope shows that La+++‐induced changes in membrane permeability or in active ion transport mechanisms are not responsible for the dramatic loss of electrolytes from experimental cells. The electrolyte loss occurs only when the cells are resuspended mechanically during the washing procedure used to prepare the cells for electrolyte determination.

We conclude that the results of La+++ interaction with Ehrlich ascites tumor cells are twofold. As we have previously reported, La+++ stabilizes and causes a hyperpolarization of the membrane potential. Secondly, La+++ predisposes the cell membrane to become highly permeable when subjected to mechanical stress.
Nuclear magnetic resonance relaxation time and self‐diffusion coefficient measurements of water in frog ovarian eggs (Rana pipiens)
Authors: Mild Kjell Hansson , James Thomas L. , Gillen Kenneth T.
Published: February 2005

Self‐diffusion coefficient measurements of water in untreated ovarian eggs of Rana pipiens using nuclear magnetic resonance indicate that cytoplasmic water has reduced translational mobility compared with pure water. Using a simple two‐state model, we find that ∼67% is “relatively immobile.” Consideration of the nuclear magnetic resonance spin‐lattice and spin‐spin relaxation times indicates that the decreased mobility can largely be ascribed to hydration. Our value for the self‐diffusion coefficient (6.8 × 10−6 cm2/sec) is lower than those reported by other investigators using isotopic water exchange techniques on frog eggs chemically treated to remove the membrane. However, the results reported here are in agreement with unpublished data on untreated frog eggs implying that chemical treatment has modified the cytoplasm in some manner.
Activation of a ribonuclease on dispersion of rat liver to a single cell suspension and incubation of the cells at 37°
Authors: Kumar B. Vijaya , Bhargava P. M.
Published: February 2005

Incubation of rat liver parenchymal cell suspensions at 37° results in degradation, to acid‐soluble material, of 15% of cellular RNA at 30 minutes and 40% at three hours, beyond which there is little, if any, further degradation. The RNA which remains in the acid‐insoluble form in the cells up to 30 minutes appears to exist largely in the native state. However, after 30 minutes, the acidinsoluble RNA of the cells is found to be partially depolym‐erised. These observations suggest the activation of an intracellular nuclease on dispersion of the liver tissue to a single cell suspension and incubation at 37°. This nuclease appears to be responsible also for the degradation, reported earlier, of exogenous RNA taken up by the cells. Activation of the nuclease is not due to depletion of pool of ATP or of other ribonucleotides from the cells, during either dispersion of the tissue or incubation at 37°. Incubation of the cells at 28°, or of liver slices at 37°, does not lead to any significant degradation to acid‐soluble material, or to partial depolymerisation, of RNA. Analysis of RNA obtained from cells incubated at 37° for various periods showed that chromatography on methylated albumin‐kiesulguhr (MAK) and Sephadex columns is not suitable for detecting partial depolymerisation of cellular RNA; RNA shown to be partially depolymerised by analysis on sucrose density gradient, in an analytical ultracentrifuge, and on a cellulose column, gave the normal pattern in MAK or Sephadex runs.
Contraction of protoplasm. IV. Cinematographic analysis of unfertilized sea urchin eggs stimulated with continuous direct current
Authors: Perkins Donald L. , Jahn Theodore L.
Published: February 2005

The response of unfertilized sea urchin eggs stimulated with continuous D.C. was studied using cinematographic techniques. As reported by previous workers, the initiation of the response was anodal in polarity and followed a typical strength‐duration curve. However, the anodal response may be swelling and/or contraction, depending on the amplitude of the applied stimulus, i.e., the magnitude of the contraction is directly related to the applied stimulus and is a graded response. It is suggested that the phenomena of anodal swelling and anodal contraction represent a continuum of responses based on ion exchange.
Physical separation of colony stimulating cells from in vitro colony forming cells in hemopoietic tissue
Authors: Moore M. A. S. , Williams N.
Published: February 2005

Hemopoietic colony formation in agar occurred spontaneously in mass cultures of marrow cells obtained from a number of species (guinea pig, rat, lamb, rabbit, pig, calf, human and Rhesus monkey). This contrasted with the observation that colony formation by mouse bone marrow exhibited an absolute requirement for an exogenous source of a colony stimulating factor. Analysis of spontaneous colony formation in Rhesus monkey marrow cultures revealed the presence of a cell type in hemopoietic tissue, capable of elaborating colony stimulating factor when used to condition media or as feeder layers. Equilibrium density gradient centrifugation separated colony stimulating cells from in vitro colony forming cells in monkey bone marrow. Separation studies on spleen, blood and marrow characterized the stimulating cells as of intermediate density, depleted or absent in fractions enriched for cells of the granulocytic series and localized in regions containing lymphocytes and monocytes. Adherence column separation of peripheral blood leukocytes showed the stimulating cells to be actively adherent, unlike the majority of lymphocytes, and combined adherence column and density separation indicated that stimulating cells were present in hemopoietic tissue within the population of adherent lymphocytes or monocytes.
The effect of cyclic AMP and cytochalasin B on tissue cultured melanophores of Xenopus laevis
Authors: Lyerla Timothy A. , Novales Ronald R.
Published: February 2005

The effects of cytochalasin B or low concentrations of adenosine 3′,5′‐monophosphate (cyclic AMP) were tested on melanophores in hanging drop preparations of neural fold explants from Xenopus laevis embryos in Barths' solution. After one week in culture, the melanophores were punctate in this medium. Cyclic AMP at 5 mM consistently caused reversible morphological transformation of these cells to the stellate state, whether they were situated within an epithelial outgrowth or isolated on the surface of the coverglass. Only the isolated melanophores consistently responded to 1 mM cyclic AMP. Cytochalasin B at 1–10 μg/ml caused aggregation of melanin granules in stellate cells, but left long, narrow cell branches containing some melanosomes. Its effect was at least partially reversible and appeared to be dose dependent. At 1% concentration, dimethyl sulfoxide caused melanin dispersion.
A cell line which is temperature‐sensitive for cytokinesis
Authors: Smith B. J. , Wigglesworth N. M.
Published: February 2005

We have isolated several cell lines which are temperature‐sensitive for growth. One of these appears to be temperature‐sensitive for cytokinesis. It was isolated from a Syrian hamster cell line by selecting cells which were not killed by 1 μg/ml cytosine arabinoside at 39° but which grew normally at 31°. It shows an increased proportion of binucleate cells when shifted to the non‐permissive temperature and time‐lapse photomicroscopy shows that a high proportion of attempted mitoses fail at 39°, apparently at the stage of cytokinesis. The cells which have failed to complete mitosis reattach to the plate and have two normal‐size nuclei but otherwise behave normally.
Fluctuations of Feulgen‐ and diphenylamine‐DNA in peripheral leukocytes,
Authors: Fontaine Julia C. , Swartz Frank J.
Published: February 2005

The circulating leukocyte is usually considered a mature, differentiated cell which does not normally divide. Cytophotometry of human and mouse leukocyte nuclei, however, reveals significant fluctuations in amounts of Feulgen‐DNA in all leukocytes at various times of the day. When analyzed for DNA content by the diphenylamine method, the same samples demonstrate variations closely correlated with those obtained by cytophotometry. Although these data may be interpreted as suggesting, among other things, the presence of metabolic DNA, a preliminary radioautographic study of the uptake of tritiated thymidine in mouse leukocytes failed to demonstrate evidence of DNA synthesis in the entire population of cells. In this study only 6–7% of the total leukocyte population was labelled over a 24‐hour period. This discrepancy, when considered in light of other uncertainties concerning the Feulgen and diphenylamine reactions, has led to reservations over the ability of either reaction to reflect the true amount of DNA in cells at all times. Rather, we consider it more likely that both procedures reveal similar incomplete fractions of leukocyte DNA at various times of the day, and that the magnitude of this fraction is, perhaps, determined by cyclic influences acting on such parameters as nuclear volume and degree of packing of the nucleohistones.
Calcium‐mediated effects of calcitonin on cyclic AMP formation and lymphoblast proliferation in thymocyte populations exposed to prostaglandin E1
Authors: Whitfield J. F. , MacManus J. P. , Franks D. J. , Braceland B. M. , Gillan D. J.
Published: February 2005

The calcitonin (SCT) from salmon ultimobranchial bodies which (like mammalian calcitonins) lowers the plasma calcium concentration in mammals can also affect cyclic AMP (cyclic adenosine 3′,5′‐monophosphate) metabolism and proliferation of lymphoblasts in normal and prostaglandin E1 (PGE1)‐treated rat thymocyte populations in three different ways. In the first case, low concentrations (0.5–5.0 ng per milliliter) of SCT lower (by a calcium‐mediated process) the ability of PGE1 to transiently increase cyclic AMP synthesis, but the reduced surge of cyclic AMP production is still ample to stimulate lymphoblasts in the cell population to initiate deoxyribonucleic acid (DNA) synthesis. Secondly, these low SCT concentrations affect the eventual progression of the PGE1‐stimulated, DNA‐synthesizing lymphoblasts into mitosis by a calcium‐mediated process. Depending on the extracellular calcium concentration and the magnitude of the initial increment in the intracellular cyclic AMP content, SCT can either promote or inhibit the progression of the stimulated cells into mitosis. SCT's third action is a rapid (within 5 minutes), calcium‐independent elevation of the cellular cyclic AMP content in otherwise untreated thymic lymphocyte populations exposed to a very high concentration (100 ng per milliliter) of the hormone. This early, transient rise in the cyclic AMP level is followed by a calcium‐dependent increase in lymphoblast proliferation. An attempt is made to interrelate and explain the different actions of SCT on cyclic AMP metabolism and mitogenesis.
Cell size distribution in the thymus as a function of age
Authors: Salinas F. A. , Smith L. H. , Goodman J. W.
Published: February 2005

Although it is well known that thymus function changes with age, it is not known whether these changes are associated with specific thymocyte populations. Since one criterion of specificity is cell size, we studied the size distribution of thymocytes from mice 0.5 days to 30.5 months of age. Body weight, thymus weight, and thymocyte yield were also measured. The mean cell volume of thymocytes from 8.5 to 13 week old mice was 326 μ3, with two detectable subpopulations. Mean thymocyte size was found to change with age. During the first postnatal week, the mean cell volume of the whole thymocyte population increased from 200 to 350 μ3, and the percentage of large cells increased greatly and constituted 90% of the whole population at four days of age. A rather slow decline in mean cell volume with some fluctuation occurred throughout the remaining life span, and at 30.5 months the mean had dropped to about 190 μ3. We suggest on the basis of these data that large thymocytes are involved in the contribution of the thymus to early postnatal development of the immune system and that the age‐related functional capacity of the thymus is related to the size of the thymocyte population.
Biochemical characteristics of normal and virally transformed mouse cell lines
Authors: Yoshikawa‐Fukada M. , Nojima T.
Published: February 2005

Normal and virally transformed mouse cells respond differently in vitro to high concentrations of potassium. A higher potassium concentration is required to inhibit multiplication of SV40 transformed 3T3 cells to the same extent as that of normal 3T3 cells. This potassium effect correlates to specific activity of Na‐K dependent ATPase in membranous fraction, normal 3T3 cells having the higher enzyme activity being more sensitive to potassium than SV40‐3T3 cells which have the lower specific activity of the enzyme.

Contact inhibition of growth and changes of concanavalin A binding sites which are characteristics of viral transformation influence specific activities of Na‐K dependent ATPase and of adenyl cyclase. Incubation with trypsinized concanavalin A causes SV40‐3T3 to show contact inhibition of growth and at the same time, higher specific activities of both enzymes than the observed in untreated cells. Cellular content of cyclic 3′,5′‐AMP of contact inhibited 3T3 is higher than that in transformed SV40‐3T3, but no difference is detectable in ATP content.
Calcium accumulation by isolated sarcoplasmic reticulum of skeletal muscle during development in tissue culture
Authors: Lough John W. , Entman Mark L. , Bossen Edward H. , Hansen James L.
Published: February 2005

The calcium uptake and ATPase activities of isolated sarcoplasmic reticulum were studied during the first six days of chick skeletal muscle maturation in tissue culture. Statistically significant increases in these activities were observed between the second and the sixth day of maturation. Increases in oxalate‐dependent calcium uptake were demonstrated at concentrations of 2.5 × 10−5 M calcium and 10−4 M calcium. Calcium‐binding determinations conducted in the absence of oxalate displayed changes manifested by an increase at day 5 followed by a significant decrease at day 6. Increases in total ATPase activity during maturation paralleled the sequential increases in calcium uptake. Calcium‐stimulated ATPase activity, however, did not change significantly during periods of marked increase in calcium uptake, suggesting that these activities are dissociated during development of the sarcoplasmic reticulum. These data demonstrate that calcium uptake and total ATPase activity increase during muscle maturation in tissue culture and that these activities are present prior to spontaneous contractions.
Effect of AMP and related compounds on glycogen content of Tetrahymena
Authors: Blum J. J.
Published: February 2005

Addition of AMP to cultures of Tetrahymena pyriformis caused an increase in glycogen content of the cells and a small inhibition of growth. Adenine, adenosine, ADP, and ATP also increased glycogen content. Inosine and GMP were less effective; cytidine and uridine were ineffective. The increase in glycogen content was also observed in cultures supplemented with ribose, fructose, or glycerol, and when glyconeogenesis was increased by partial anaerobiosis. Adenine itself did not serve as a glycogen precursor, nor could the lipids of the cell have been the source of the carbon for the increased glycogen. The specific activity of glycogen from cultures supplemented with labelled amino acids was lower in AMP‐treated cells than in controls. AMP‐treatment had little effect on 14CO2 production from labelled glucose, acetate, or pyruvate, but baused a marked inhibition of the oxidation of labelled glyoxylate. It was suggested that AMP increases the rate of glyconeogenesis from precursors other than amino acids and interferes with malate synthase activity or malate transfer from peroxisomes to mitochondria.
Heats of activation for the exosmotic flow of water across the membrane of leucocytes and leukemic cells
Authors: Hempling Harold G.
Published: February 2005

The permeability of the membranes of different types of leucocytes from several mammalian species to the exosmotic flow of water has been measured at different temperatures. Heats of activation for the process have been calculated. Results indicate that the leucocyte has an unusually high heat of activation for the osmotic movement of water across its outer membrane, ranging between 13 to 18 kcal/mole. Unconstrained water movement usually has values between 3 to 5 kcal/mole. This property characterizes all leucocytes examined to date, regardless of species or type. It is apparent that water is intimately associated with the outer boundary of the cell and that this association is quite sensitive to the structural changes which must occur in response to changes in temperature.
A low molecular weight factor in lung‐conditioned medium stimulating granulocyte and monocyte colony formation in vitro
Authors: Sheridan J. W. , Metcalf D.
Published: February 2005

Medium conditioned by excised whole lungs from endotoxin‐injected C57BL mice was highly active in stimulating hemopoietic colony formation, particularly of granulocytic type, in agar cultures of mouse bone marrow cells. The colony stimulating factor (CSF) in this material had an α1‐α2 electrophoretic mobility, was eluted from calcium phosphate gel by 0.04 M phosphate buffer and had an unusually low apparent S20W of 1.9. Sequestered polymor‐phonuclear neutrophils were excluded as a major source of this CSF. The high specific activity and ease of preparation of lung conditioned medium make it valuable both for the large scale production of CSF and as a source of an unusual type of CSF.
The response of normal and polyoma virus‐transformed BHK/21 cells to exogenous purines
Authors: Clarke G. D. , Smith Carole
Published: February 2005

Adenosine (10 μM) stimulates the initial growth rate of BHK/21 cells seeded at low but not high density in monolayer culture; it does not affect final cell density or permit growth in agar. In labelling experiments With tritiated thymidine, adenosine also increases the response of quiescent cells to low concentrations of serum. Dialysis of serum to remove oxypurines only marginally reduces its effect on quiescent cell labelling or growth, indicating that BHK/21 cells are able to synthesise purines. The response of quiescent cells to 5% serum is inhibited by high MW (2 × 106) dextran sulphate at 2 μg per milliliter. Low MW dextran sulphate (30,000) and heparin at 20 μg per milliliter produce the same effect. Exogenous adenosine (10 μM) prevents this inhibition. Many other purine derivatives replace adenosine for all the above activities but xanthine is completely inactive in all. It, therefore, appears that nucleotide synthesis is a necessary function of these compounds.

The growth of cells of a polyoma‐virus‐transformed BHK/21 line in monolayer is not stimulated by exogenous purine, though their colony‐forming ability in agar is increased five‐fold. The stimulating effects of exogenous purines on normal BHK/21 cells and the absolute requirement for them in the presence of polyanions is discussed in relation to possible mechanisms of growth control.
Histone mediated changes in morphology and confluent density of cultured cells
Authors: Kolodny G. M.
Published: February 2005

Calf thymus histones and histone subfractions were added to media overlying subconfluent mouse fibroblast cells in culture. The histones caused significantly higher cell densities at confluence than control cultures and disruption of the normal ordered arrangement of cells. These changes were seen on application of histones to growing cells but not confluent cells and were reversed when the histones were removed and the cells replated with more growth area. The slightly lysine rich histone fraction had the greatest effect and the lysine rich fraction had the least effect on cell morphology and cell number at confluence. These effects could not be duplicated with other highly charged basic proteins.
The ability of calcium to change cyclic AMP from a stimulator to an inhibitor of thymic lymphoblast proliferation
Authors: Whitfield J. F. , MacManus J. P. , Gillan D. J.
Published: February 2005

Calcium is a major regulator of thymic lymphoblast proliferation in vivo and in vitro. The proliferative activity of the lymphoblasts in thymic lymphocyte (thymocyte) populations in vitro is both constant and low in the presence of calcium concentrations between 0 and 1.0 mM, but higher concentrations increase proliferation by an endogenous cyclic AMP‐mediated promotion of the initiation of DNA synthesis.

Lower concentrations (10−7 to 10−5 M) of exogenous cyclic AMP (but not 5′‐AMP) stimulate lymphoblast proliferation in a low‐calcium (0.5 mM) medium, but higher concentrations do not. However, all exogenous cyclic AMP concentrations between 10−7 and 10−3 M (but again not 5′‐AMP) block the stimulation of lymphoblast proliferation in a high‐calcium (1.5 mM) medium. Exogenous cyclic AMP does not prevent calcium from “activating” lymphoblasts, but it reversibly blocks the reaction responsible for the initiation of DNA synthesis in these stimulated cells. Finally, cyclic AMP's inhibitory action, in contrast to its stimulatory action in low‐calcium medium, is not specific for the cyclic nucleotide since a low, non‐mitogenic concentration of cyclic GMP also prevents calcium from stimulating DNA synthesis and cell proliferation.
The effect of trypsin on membrane transport of non‐electrolytes
Authors: Tsan Min‐Fu , Taube Rebekah A. , Berlin Richard D.
Published: February 2005

Trypsinization of alveolar macrophages depresses lysine transport but has no effect on nucleoside transport. The depression of the initial rate of lysine transport is due to a decreased rate of exchange diffusion presumably secondary to lowered intracellular pools of amino acids. It is shown directly that trypsinization accelerates the efflux of amino acids but not certain other metabolites, and reduces the capacity of the cell to concentrate amino acids.
Genetics of somatic mammalian cells. XVII. Induction and isolation of chinese hamster cell mutants requiring serine
Authors: Jones Carol , Puck Theodore T.
Published: February 2005

The induction, isolation and some of the properties of serine‐requiring mutants of Chinese hamster ovary cells have been described. These cells promise to be useful in biochemical genetic studies and cancer research.
A Calcium‐sensitive lanthanum inhibition of amoeboid movement
Authors: Hawkes R. B. , Holberton D. V.
Published: February 2005

The effects of lanthanum ions upon amoeboid movement and upon the redistribution of dense cytoplasmic inclusions following centrifugation were investigated in Amoeba discoides. Treatment with low lanthanum concentrations produced a characteristic inhibited condition in which locomotion ceased while saltatory movements continued. The resorting of stratified cytoplasm by local internal cytoplasmic flow was unaffected. This contrasted with p‐hydroxymercuribenzoate treatment which inhibited both locomotion and saltatory movements. The inhibitory effects of lanthanum ions were antagonised by calcium ions but not by magnesium ions. It is reasoned that lanthanum competes for a peripheral binding site thereby disrupting a calcium‐mediated regulatory mechanism of amoeboid movement.
Cellular responsiveness to stimulation in vitro: Strain differences in hemopoietic colony forming cell responsiveness to stimulating factor and suppression of responsiveness by glucocorticoids
Authors: McNeill T. A. , Fleming W. A.
Published: February 2005

Granulocyte‐macrophage colony formation from bone marrow cells in soft agar is dependent upon the presence of a stimulating factor and the number of colonies is related to its concentration. This dose‐response effect provided a measurement of the responsiveness to stimulation of colony forming cell populations in marrows from different sources. There were significant differences between the responsiveness of cells from different strains of mice which paralleled the previously observed myelopoietic and immune responsiveness of these strains to stimulation in vivo.

Low concentrations of hydrocrotisone reduced the responsiveness of colony forming cells (a) when added to cultures of normal marrow or (b) when cells were taken from hydrocortisone‐treated mice and cultured in its absence. The reduction which followed inoculation was not apparent until the 4th day and occurred irrespective of mouse strain, type of drug or route of inoculation and with a dose (100 μg) which did not affect the actual number of colony forming cells in the marrow.
The effect of extracellular calcium and magnesium on the proliferation of murine lymphoblasts
Authors: Brennan James K. , Lichtman Marshall A.
Published: February 2005

We have shown that the murine lymphoblast, L5178Y, requires extracellular magnesium or calcium for proliferation in suspension culture. Although both cations produce biphasic effects on growth, magnesium is the more potent since it: (1) stimulates proliferation at lower concentrations; (2) supports optimal proliferation over a wider concentration range; (3) maintains higher cell densities at stationary phase; and (4) produces less inhibition at high concentration.

At suboptimal concentrations, calcium facilitates the effect of magnesium but at optimal concentration, no facilitation is evident. A concentration of 3.2 mM calcium or magnesium inhibits growth, while the same concentration composed of equimolar calcium and magnesium does not inhibit proliferation.

Extracellular calcium and magnesium may influence proliferation by effecting changes in intracellular calcium and magnesium since: (1) reduction in extracellular concentrations sufficient to produce decreased growth rate is associated with decreased cell calcium and magnesium; (2) cell magnesium and growth rate are related such that an exponential decrease in relative doubling time occurs with decrease in cellular magnesium.

Cells cultured at 37°C in magnesium and calcium‐deprived medium will proliferate at a normal rate if either or both cations are replaced within six to 10 hours; however, with longer deprivation the doubling time in restored medium is progressively lengthened.
Isolation and characterization of revertant cell lines. IV. Direct selection of serum‐revertant sublines of SV40‐transformed 3T3 mouse cells
Authors: Vogel A. , Pollack R.
Published: February 2005

SV101, the SV40‐transformed subline of the mouse fibroblast line 3T3, is both serum‐ and density transformed, since it grows in both 1% and 10% calf serum, and grows beyond confluence in 10% calf serum. Negative selection at low cell density in 1% calf serum or in 10% agamma‐depleted serum permits direct recovery of serum‐revertant sublines of SV101. These sublines are unable to grow in 1% calf serum.

Although negative selection at high cell density in 10% calf serum is known to permit recovery of density‐revertant sublines of SV101, most density‐revertants are not serum‐revertant. However, all serum‐revertants isolated so far are density‐revertant as well.
ph, serum and Zn++ in the regulation of DNA synthesis in cultures of chick embryo cells
Authors: Rubin H.
Published: February 2005

Variations in pH, serum concentration and the availability of Zn++ in the medium markedly influence the initiation of DNA synthesis in cultured chick embryo cells. This report considers the interplay of these factors with one another and with other factors such as type of medium, cell population density and the malignaut transformation in an attempt to better define the variables of the growth control system. Conditioned medium seems to protect the cells against the inhibitory effects of lowered pH. Increased serum concentration has a similar, but more striking effect. Increased serum concentration and pH, as well as decreased population density, which stimulate DNA synthesis, also lower the sensitivity of DNA synthesis to inhibition by Zn++ deprivation. Likewise, cell transformation by infection with Rous sarcoma virus lowers the sensitivity of DNA synthesis to inhibition by Zn++ deprivation and by pH reduction. The response of DNA synthesis to pH varies with the type and concentration of buffer used. It is concluded that there are a number of mutually interacting variables involved in the regulation of animal cell multiplication.