bluuebunny/crossref_metadata_2025_split huggingface dataset:
Osmotic properties of a proliferating and differentiating line of cells from the bone marrow of the rat
Authors: Cicoria A. D. , Hempling H. G. 
Published: February 2005

AbstractThe effects of cellular differentiation on the osmotic properties of a proliferating line of bone marrow cells has been investigated. This population proliferated and differentiated into distinct maturation phases which have been separated quantitatively by velocity sedimentation at 1g in a Ficoll gradient.Certain osmotic characteristics were evaluated. The volume of osmotically active water increased linearly with maturation. The osmotically inactive volume was variable during proliferation and maturation. Several correlations that concerned the exosmotic movement of water were noted, as follows: (1) membrane permeability to water increased with an increase in the diameter of the nucleus, (2) the ratio of osmotically active water to mean corpuscular volume increased with an increase in the diameter of the nucleus, (3) membrane permeability to water increased with an increase in the osmotically active water normalized to the mean cell volume, and (4) the heat of activation associated with the permeability of the membrane to water increased during maturation and varied inversely with the ratio b/MCV.These results were used to assess the effects of cellular maturation on membrane function and the state of water in a maturing cell population. The permeability data suggest that charged groups on membrane proteins and phospholipids can vary the state of water in the membrane from a thermodynamically mobile state to an “ice‐like” state. These unusual properties may be a direct result of a dynamic and functional relationship between cellular water and active biological macromolecules.
Similarities between alkaline phosphatase and CA2+ ATPase activities in HeLa cells
Authors: Brahmacupta Prem , Melnykovych George 
Published: February 2005

AbstractParallel changes in the enzyme activities of Ca2+ ATPase and alkaline phosphatase were observed in HeLa cells. Both enzymes were inhibited to a similar degree by L‐phenylalanine, L‐tryptophan, and L‐leucine, while being relatively resistant to L‐homoarginine. Exposure to heat (56°C, 60°C, and 65°C) resulted in a loss of both enzyme activities. Both alkaline phosphatase and Ca2+ ATPase, when treated with EGTA, required Ca2+ for the restoration of activity. Cells grown in the presence of agents that affect alkaline phosphatase (dexamethasone, butyric acid, and hyperosmolar NaCl) showed similar changes in the activities of both enzymes.
Chemical and biological properties of a growth factor from human‐cultured osteosarcoma cells: Resemblance with platelet‐derived growth factor
Authors: Heldin Carl‐Henrik , Westermark Bengt , Wasteson Åke 
Published: February 2005

AbstractA human osteosarcoma cell line, U‐2 OS, cultured under serumfree conditions, was shown to produce a growth factor (osteosarcoma‐derived growth factor, ODGF) for human‐cultured glial cells, fibroblasts, and other cells. ODGF, collected from the spent medium of 2 OS cultures, was purified by a sequence involving heparin‐Sepharose chromatography, hydrophobic chromatography, gel chromatography, and preparative gel electrophoresis in SDS. Purified ODGF, at a concentration of 3 ng/ml, elicited a mitogenic response in human glial cells equivalent to 50% of that afforded by human serum at a final concentration of 1%. The preparation was estimated to be > 50% pure.The biological activity of ODGF resided in a cationic, relatively heat‐resistant, reduction‐susceptible protein with a molecular weight of 30,000 (by gel chromatography and SDS‐gel electrophoresis). The electrophoretic behaviour of radioiodinated ODGF suggested that the protein was composed of two different polypeptide chains (about 13,000‐14,000 and 16,000‐17,000 daltons, respectively) linked via disulphide bonds. The molecular makeup of ODGF was thus similar to that of platelet‐derived growth factor. 125I‐ODGF could be precipitated by an antibody to platelet‐derived growth factor, indicating that the two factors were immunologically related. Resemblance with platelet‐derived growth factor was also indicated by the finding that the latter (but not, e.g., fibroblast growth factor or epidermal growth factor) competed with 125I‐ODGF for binding to human‐cultured glial cells.
Decreased initiation of DNA synthesis in a temperature‐sensitive mutant of hamster cells
Authors: Eilen Eric , Hand Roger , Basilico Claudio 
Published: February 2005

AbstractWe have analyzed ongoing DNA replication in ts BN‐2, a dna− mutant of BHK‐21 cells (Nishimoto et al. '78). At the non‐permissive temperature of 39.5°C, inhibition of 3H‐thymidine into acid‐precipitable material begins 1 to 2 h after the cells are released from a block at the start of the S‐phase. The fraction of nuclei incorporating 3H‐thymidine is similar to that of wild‐type cells through the synchronized S‐phase of 8 h. Alkaline sucrose gradient analysis shows tht pulse‐labeled DNA from mutant cells is incorporated into high molecular weight material after 3 h at eithr the permissive or non‐permissive temperature. DNA fiber autoradiograms reveal that, at 39.5°C, the rate of replication fork movement is about 30% increased in the mutant as compared to wild‐type cells. In the mutant cells, however, the interval between adjacent initiation sites is increased and the relative frequency of initiation events is decreased at the restrictive temperature. The results indicate that there is a block to ongoing replication in ts BN‐2 at the level of initiation of synthesis on individual replication units; elongation of nascent chains is not inhibited.
Compartmentalized ATP pools produced from adenosine are nuclear pools
Authors: Rapaport Eliezer 
Published: February 2005

AbstractIncubation of African green monkey kidney (BS‐C‐1) cells and mouse fibroblasts (3T6) in the presence of adenosine for 4 hours resulted in increases in the nuclear compartment pools of adenosine 5′‐triphosphate (ATP) and nuclear ATP/adenosine 5′‐diphosphate (ADP) ratios. Adenine and inosine, which yield increases in total cellular ATP pools and ATP/ADP ratios similar to those promoted by adenosine, do not produce similar increases in the nuclear compartment. Adenosine‐promoted increases in nuclear ATP pools were higher in the untransformed, serially propagated, BS‐C‐1 cells than in the spontaneously transformed 3T6 cells. Adenosine‐promoted compartmentalized ATP pools in primary chick embryo fibroblasts were reduced upon transformation of these cells with Rous sarcoma virus, resulting in free mixing of all the ATP pools synthesized from various salvage precursors. The growth regulatory properties of the nuclear compartment pools of adenine nucleotides is suggested by the big increases in nuclear ATPase and adenosine 5′‐monophosphate (AMP) demainase activities upon the entry of 3T6 cells into the S phase of their cycle. These enzymatic activities would tend to lower the nuclear ATP/ADP ratios and reduce the total adenine nucleotide pools in these nuclei respectively – conditions which were shown by earlier in vitro studies to be favorable to DNA replication.
Influence of proliferative rates and a system substrate availability on proline transport in primary cell cultures of the R3230AC mammary tumor
Authors: Gay Roger J. , Hilf Russell 
Published: February 2005

AbstractRegulation of A system amino acid transport was studied in primary cultures of the R3230AC mammary adenocarcinoma. Higher rates of carrier‐mediated Na+‐dependent proline transport, vc, was decreased and was attributed to a two‐fold decrease in Vmax and a two‐fold increase in Km. When compared to cells grown in standard media (Eagle's minimal essential medium, MEM), cells grown in media supplemented with A system substrates (alanine, serine, glycine, and proline) demonstrated adaptive decreases in proline transport; the decrease was due to two‐fold reduction in Vmax, with no change in Km for proline. Even in the presence of preferred substrates for the A system, a density‐dependent decrease in proline transport was manifested. Both fast‐ and slow‐growing cultures maintained in MEM exhibited rapid increases in proline transport when switched to buffers devoid of amino acids; two‐fold increases in Vmax were seen within 4 hr, but Km was unchanged. This starvation‐induced adaptation was completely prevented by inclusion in the buffer of 10 mM proline, 0.1 mM ‐(methylamino)‐isobutyric acid (MetAIB) or 10 mM serine, whereas inclusion of the poorer A system substrate, phenylalanine (10 mM), had no effect. The effects of MetAIB to prevent starvation‐induced increases in proline transport were dose‐related, rapid, and reversible. Amino acid starvation‐induced increases in proline transport were partially blocked by cycloheximide or actinomycin D. Data were obtained demonstrating a temporal relationship between increasing intracellular [proline] and decreasing vc for proline uptake. In addition, efflux of proline from preloaded cells preceded the increase in initial rates of proline entry. Taken together, we concluded that: (1) A system transport in primary cultures of this mammary adenocarcinoma is regulated by cell density as well as by availability of A system substrates, but these two types of regulation are kinetically distinct; and (2) starvation‐induced enhancement of proline transport appears to be due to release from transinhibition, but may also involve a derepression‐repression type of mechanism.
Mammalian cells do not have a stringent response
Authors: Pollard J. W. , Lam T. , Stanners C. P. 
Published: February 2005

AbstractA key attribute of the stringent response of bacteria is the rapid inhibition of ribosomal RNA synthesis mediated by unusual nucleotides in response to uncharged tRNA. The question as to whether mammalian cells show a stringent response analogous to that of bacteria was critically tested by the effective rapid amino acid starvation of both normal and transformed cells. Rapid starvation giving a high proportion of uncharged tRNA for leucine was produced within 7 minutes of expression of a nonleaky ts leucyl tRNA synthetase mutation in transformed CHO cells (tsH1) and in its normal growth control revertant (L‐73). To control for the effect of temperature alone, tsrevertants of tsH1 and L‐73 were included in the study, and to control for effects due simply to the inhibition of protein synthesis, the translational elongation inhibitor cycloheximide was used. In addition, rapid starvation for histidine was effected by incubation of both the CHO cell lines and of freshly explanted normal Chinese hamster embryo fibroblasts in histidine‐free medium containing high concentrations of histidinol.The rate of preribosomal RNA synthesis and the extent of its maturation to mature rRNA was measured using (3H‐methyl) methionine as a donor of methyl groups during synthesis and methylation of pre‐rRNA. There was no effect on pre‐rRNA synthesis of the rapid generation of uncharged tRNA for 45 minutes for any of the cell types tested. A nonspecific inhibition of maturation of 18S rRNA and late (3 hour) inhibition of pre‐rRNA synthesis was observed, but could be mimicked by the inhibition of protein synthesis to comparable levels with cycloheximide. Less severe amino acid starvation resulting in a more physiological inhibition of protein synthesis to 30% also had no specific effect on pre‐rRNA synthesis and maturation.Intracellular nucleotide pools were also examined for the appearance of unusual nucleotides such as guanosine tetraphosphate or pentaphosphate and for changes in the levels of normal nucleotides after severe amino acid starvation. No such changes could be detected.We conclude that although mammalian cells may have some biochemical reactions which respond to uncharged tRNA, they do not possess a macromolecular control system analogous to the stringent response of bacteria.
Human dermal microvascular endothelial cells in vitro: Effect of cyclic AMP on cellular morphology and proliferation rate
Authors: Davison P. M. , Karasek M. A. 
Published: February 2005

AbstractMacrovascular endothelial cells isolated from the human umbilical vein and microvessel endothelium from the newborn foreskin dermis differ in their requirements for optimal growth in vitor. In the presence of 5 x 10−4 M dibutyryl cyclic AMP (Bt2cAMP), human dermal microvessel endothelial cell proliferation rate increased to give a cell number of 203% of control values by day 10 in culture. The cells retained their characteristic endothelial cell morphology, reached confluence, and could be serially passaged. Cells grown in the absence of Bt2cAMP did not proliferate readily and grew in a disorganized pattern. The effect of Bt2cAMP on microvascular endothelial cell proliferation rate and morphology could be duplicated by cholera toxin (CT) used together with isobutyl methyl‐xanthine (IMX). These agents were found to elevate intracellular levels of cyclic AMP in microvascular endothelium over 40‐fold. Human umbilical vein cells in culture failed to respond to either Bt2cAMP or CT together with IMX.The growth‐promoting effect of dibutyryl cyclic AMP (Bt2cAMP) on human foreskin dermal microvascular endothelium in vitro is in marked contrast to the lack of response of human umbilical vein cells. These results provide further evidence of differences in the mechanisms that regulate macro and microvessel endothelial cell proliferation in vitro.
A unitary cause for the exclusion of NA+ and other solutes from living cells, suggested by effluxes of NA+, D‐arabinose, and sucrose from normal, dying, and dead muscles
Authors: Ling Gilbert N. , Walton Cheryl L. , Ochsenfeld Margaret M. 
Published: February 2005

Abstract1. The effluxes of labeled Na+, D‐arabinose, and sucrose from normal muscle and muscle poisoned with low concentrations of iodoacetate were studied. The procedure involved repeated loading with isotope, followed by washing of the same muscle while still normal and at different states of dying. 2. The rates of Na+ efflux in both the fast and slow fraction remained either quite constant or showed some unpredictable, minor fluctuations. This was true for both Na+ and the two sugars studied, confirming earlier conclusions that the steady levels of these solutes were not maintained by pumps. 3. In all cases studied, the efflux curves showed at least two fractions. It is the fast‐exchanging fraction that steadily and consistently increased in magnitude as the muscles were dying, until finally the concentration of solute in this fraction reached and sometimes surpassed the labeled solute concentrations in the original labeled solutions in which the muscles were equilibrated. The slow fractions showed only a transient increase or none at all. These observations show that it is the fast fraction that represents solute dissolved in cell water and rate‐limited by passage through the cell surface and that the partial exclusion of Na+ and the sugars have a unitary cause—a reduced solubility in the cell water which in the presence of ATP exists in the state of polarized multilayers.
The membrane potential of Ehrlich ascites tumor cells: An evaluation of the null point method
Authors: Smith Thomas C. , Robinson Susan C. 
Published: February 2005

AbstractThe effects of valinomycin (25 pM) on the membrane potential and on initial, passive Na+ and K+ movements have been determined in Ehrlich ascites tumor cells. The membrane potential of steady‐state cells in a physiologic environment was – 23.2 mV. Addition of valinomycin induced a small, significant hyperpolarization (Vm = –29.6 mV) when averaged over the population tested. However, analyses of the response of individual cells to valinomycin showed two different potential effects: (1) the majority of cells hyperpolarized after treatment; but (2) a significant fraction depolarized when exposed to valinomycin. The Vm of steady‐state cells incubated in saline with K+ at concentrations of 21 mM or 75 mM was – 21.4 mV and –22.0 mV, respectively. Addition of valinomycin to these cells was without effect on Vm, thus establishing the “null point” responses. Only for cells incubated in saline with a K+ of 75 mM was there agreement between Vm and K+ equilibrium potential (Vk). Determinations of cellular Na+ and K+ showed that valinomycin induced net losses of K+ and gains of Na+ by cells incubated in either physiologic saline or saline with a K+ concentration of 21 mM. However, the celular K+ of cells incubated in saline with a K+ concentration of 75 mM was unaltered by valinomycin. There was a two‐ to threefold increase in K+ permeability of the cell membrane in the presence of valinomycin. These results are consistent with the existence of two null points in the membrane‐potential response to valinomycin: One is established when the membrane potential corresponds to Vk; the second occurs when the effects of valinomycin on K+ loss from the cell are exactly offset by its inhibition of active Na+ + K+ transport.
Distribution of the inducer of differentiation bis‐acetyl‐diaminopentane in murine erythroleukemia cells
Authors: Tsiftsoglou Asterios S. , Bhargava Kuldeep K. , Rittmann Lana S. , Sartorelli Alan C. 
Published: February 2005

AbstractExposure of murine leukemia cells in culture to bis‐acetyl‐diaminopentane (BADP) caused erythroid maturation as measured by the accumulation of hemoglobin in treated cells. The appearance of differentiated cells in cultures exposed to BADP occurred 18 to 20 hours earlier than in those treated with dimethylsulfoxide (DMSO), a standard inducer of differentiation in this system. Studies with [3H]BADP indicated the occurrence of relatively rapid association of the inducer with cells, and subsequent linear accumulation. Fractionation of cellular components and measurement of radioactivity from BADP therein demonstrated that this agent preferentially associates with a fraction enriched for plasma membrane. In addition, [3H]BADP was capable of binding to the plasma membrane‐enriched fraction isolated from murine erythroleukemia cells as measured by gel filtration. These findings support the concept that interaction of inducers of murine erythroleukemia differentiation such as BADP with components of the surface membrane may be important in the cascade of events that lead to the erythroid maturation of these leukemic cells.
Inhibition of BALB/c‐3T3 cells in late G1: Commitment to DNA synthesis controlled by somatomedin C
Authors: Wharton Walker , Van Wyk Judson J. , Pledger W. J. 
Published: February 2005

AbstractMethylglyoxal bis‐(guanylhydrazone) (mGBG) blocked the stimulation of DNA synthesis in quiescent, density‐inhibited BALB/c‐3T3 cells treated with platelet‐derived growth factor (PDGF) and platelet‐poor plasma (PPP). Competence formation produced by a transient exposure to PDGF was not effected by mGBG. In contrast, mGBG effectively inhibited the PPP‐stimulated progression of competent cells through the G1 phase of the cell cycle, although maximal inhibition was observed when mGBG was present during both the exposure to PDGF‐ and PPP‐supplemented media. When quiescent cells were treated with PDGF and PPP‐supplemented media in the presence of mGBG for 12–18 hours and the mGBG was then removed, cells entered the S phase after a 4 hour lag. The rate of entry into the S phase, but not the time necessary for the cells to progress from the mGBG block into the S phase, was dependent on the concentration of PPP present after removal of the mGBG. Either somatomedin C or insulin, but not epidermal growth factor, fibroblast growth factor, or PDGF were able to substitute for PPP in allowing cells to enter the S phase after the cells were released from the mGBG block. A marked inhibition of (3H)‐leucine incorporation in serum‐stimulated cultures was produced at mGBG concentrations which caused no decrease in the amount of (3H)‐uridine incorporated during a short (15 minute) pulse. The ability of hormones to allow cells to progress to the late G1 phase and become committed to DNA synthesis after a mGBG inhibition was not related to their ability to restore the normal rate of protein synthesis as determined by (3H)‐leucine incorporation.
Factors in the rat submaxillary gland that stimulate growth of cultured glioma cells: Identification and partial characterization
Authors: McClure D. B. , Ohasa S. , Sato G. H. 
Published: February 2005

AbstractThe effect of rat submaxillary extract on the growth of rat C6 glioma cells in serum‐free culture has been examined. Extracts (10–15 μg/ml) of submaxillary glands from both male and female rats markedly enhanced the growth of serum‐deprived C6 cells and, in combination with insulin, transferrin, and NIH‐LH (a source of fibroblast growth factor), were able to stimulate C6 cell growth to an extent comparable to that achieved with an optimal amount of fetal calf serum. The mitogenic activity of rat submaxillary extracts was found to be heat‐labile, acid‐stable, and partially inactivated by protease and 2‐mercaptoethanol. Under our assay conditions, biologically active preparations of purified mouse submaxillary gland epidermal growth factor (EGF) or nerve growth factor (NGF) were not mitogenic for C6 cells, nor was the mitogenic activity of rat submaxillary extracts inhibited by antiserum to these mouse submaxillary gland growth factors. These results suggest that the active component(s) of rat submaxillary extracts is unrelated to either EGF or NGF. The growth‐enhancing effect also appears unrelated to esteropeptidase activity present in these extracts since the mitogenic activity was unaffected by several protease inhibitors. Moreover, two purified mouse submaxillary gland arginylesteropeptidases, EGF‐binding protein and γ‐subunit of 7 S NGF, were unable to elicit a comparable growth response even when added to cell culture medium at unreasonably high concentrations.The C6 cell mitogenic activity of crude submaxillary extracts could be separated into two biologically similar components by either gel filtration on Sephadex G‐100, preparative isoelectric focusing in a pH gradient of 3–10, or adsorption to DEAE‐cellulose followed by elution with a sodium chloride gradient. One of the active components was acidic in nature and had an apparent molecular weight of 40,000, while the other was near neutral in charge and possessed a molecular weight of approximately 20,000. The relationship between these two C6 cell mitogenic components and the rat submaxillary gland component responsible for stimulating Balb/c‐3T3 cell growth in serum‐free, factor supplemented medium (McClure et al., 1979, J. Cell Biol. 83: 96a) is also discussed.
The role of respiration in tumor cell transition from the noncycling to the cycling state
Authors: Olivotto Massimo , Paoletti Francesco 
Published: February 2005

AbstractResting Yoshida AH130 hepatoma cells, harvested at the plateau of tumor development in vivo, were recruited into the cycling state following transfer to an in vitro system whereby these cells were incubated in the autologous ascites plasma diluted with buffered saline and enriched with glucose. In this system, cell recruitment into the phase of DNA synthesis (S phase) strictly depends on the activity of the respiratory chain and is abolished by anaerobiosis as well as by antimycin A, although the intracellular levels of ATP and the rate of protein synthesis are practically unaffected by these treatments. Furthermore, 2,4‐dinitrophenol, at concentrations which uncouple the respiratory phosphorylation and hence enhance both glycolysis and oxygen consumption, does not hinder cell promotion into S phase. Thus, the absolute respiration dependence of cycling resumption by resting ascites cells does not seem to rely on respiratory ATP supply, but rather is linked to the electron flow through the respiratory chain.