bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of hyperosmolarity on the activity of amino acid transport system L in avian fibroblasts
Authors: Tramacere Mariarosaria , Petronini Pier Giorgio , Borghetti Angelo F. 
Published: February 2005

AbstractThe transport of selected neutral amino acids known as good substrates of amino acid transport System L has been studied in chick embryo fibroblasts exposed for 4 hours to hyperosmolar culture medium. The activity of the L system, as measured by initial rates of L‐phenylalanine uptake, increased in hyperosmolarity treated cells when determined before any cell depletion of intracellular amino acids. This effect was lost after depletion but reappeared after reloading the cells with pertinent substrates of System L. This transport activity appeared to be related to the internal level of amino acids capable of exchange through System L. In hyperosmolarity‐treated chick embryo fibroblasts a higher level of System L substrates was obtained during the reloading phase in comparison to control cells. This expanded amino acid pool reflected an increased activity of transport System A, an agency of amino acid mediation known to enlarge its capacity following a hyperosmolar treatment of chick embryo fibroblasts (see Tramacere et al., 1984). L‐Methionine, a preferred substrate of both A and L systems, appeared to be involved in the coupling between the activity of amino acid transport Systems A and L in these cells.
Temperature‐dependent transmembrane potential changes in cells infected with a temperature‐sensitive moloney sarcoma virus
Authors: Lai C. N. , Gallick G. E. , Arlinghaus R. B. , Becker F. F. 
Published: February 2005

AbstractNormal rat kidney cells (NRK) infected with the temperature‐sensitive (ts) transformation mutant of Moloney murine sarcoma virus yielded a clone of cells, 6m2, that exhibited a transformed morphology at 33°C and a normal morphology at 39°C. Transmembrane potential (Em) was measured fluorometrically using a cyanine dye diS‐C3‐(5). Fluorescence was inversely correlated with Em. Cells at 33°C had lower Em. Em changes were recorded within 15 minutes of temperature shift from 33°C to 39°C in both directions, increasing in the 33°C to 39°C direction and decreasing in the 39°C to 33°C direction. Uninfected NRK cells when shifted under the same condition exhibited small fluorescence changes in the 33°C to 39°C direction. Shifting from 39°C to 33°C resulted in Em changes similar to those in 6m2 cells. Also studied was a cell line infected with a spontaneous revertant of the ts mutant, designated 54‐5A4; it was transformed at both temperatures. Shifting from 33°C to 39°C in both directions yielded small changes. Transmembrane potential changes in 6m2 cells precede other transformation‐specific changes that occur after a temperature shift.
The role of increased proteolysis in the atrophy and arrest of proliferation in serum‐deprived fibroblasts
Authors: Gronostajski Richard M. , Goldberg Alfred L. , Pardee Arthur B. 
Published: February 2005

AbstractWhen cultured fibroblasts are deprived of serum, the degradation of long‐lived proteins and RNA increases, the cells stop proliferating, and they decrease in size. To determine the role of the increased protein catabolism in these responses, we studied the effects of inhibitors of intralysosomal proteolysis in Balb/c 3T3 cells. When these cells were placed in serum‐deficient medium (0.5% serum), the rate of degradation of long‐lived proteins increased about twofold within 30 min. This increase was reduced by 50‐70% with inhibitors of lysosomal thiol proteases (Ep475 and leupeptin) or agents that raise intralysosomal pH (chloroquine and NH4Cl). By contrast, these compounds had little or no effect on protein degradation in cells growing in 10% serum. Thus, in accord with prior studies, lysosomes appear to be the site of the increased proteolysis after serum deprivation. When 3T3 cells were deprived of serum for 24‐48 hours, the rate of protein synthesis and the content of protein and RNA and cell volume decreased two‐ to fourfold. The protease inhibitor, Ep475, reduced this decrease in the rate of protein synthesis and the loss of cell protein and RNA. Cells deprived of serum and treated with Ep475 for 24‐48 hours had about twice the rate of protein synthesis and two‐to fourfold higher levels of protein and RNA than control cells deprived of serum. The Ep475‐treated cells were also about 30% larger than the untreated cells. Thus, the protease‐inhibitor prevented much of the atrophy induced by serum deprivation. The serum‐deprived fibroblasts also stopped proliferating and accumulated in the G1 phase of the cell cycle. The cells treated with Ep475 accumulated in G1 in a manner identical to untreated serum‐deprived cells. Other agents which inhibited protein breakdown in serum‐deprived cells also did not prevent the arrest of cell proliferation. Thus the enhancement of proteolysis during serum deprivation appears necessary for the decrease in size and protein synthesis, but probably not for the cessation of cell proliferation. When cells deprived of serum in the presence or absence of Ep475 were stimulated to proliferate by the readdition of serum, the larger Ep475‐treated cells began DNA synthesis 1–2 hours later than the smaller untreated cells. Thus, after treatment with Ep475, the rate of cell cycle transit following serum stimulation was not proportional to the cell's size, protein, or RNA content, or rate of protein synthesis.
Apparent heterogeneity in the response of quiescent swiss 3T3 cells to serum growth factors: Implications for the transition probability model and parallels with “cellular senescence” and “competence”
Authors: Brooks Robert F. , Richmond Frances N. , Riddle Peter N. , Richmond K. M. Veronica 
Published: February 2005

AbstractWhen subconfluent, Swiss 3T3 cells made quiescent by serum deprivation are stimulated with low concentrations of serum (ca. 1%), only a proportion of them (roughly 50%) enter S phase despite daily replacement with fresh, low‐serum medium. The cells that fail to enter S phase are not incapable of doing so, since most of them initiate DNA synthesis after transfer to 10% serum. It would appear that individual cells vary in their growth factor requirements. Using time‐lapse cinemicroscopy a few of the cells that respond to low serum were seen to give rise to several generations of progeny, while the majority of cells failed to divide at all, or divided once at most. Despite this, differences between cells in growth factor requirements do not seem to be heritable in the long term, since attempts to enrich for responding cells by prolonged culture in 1% serum have been unsuccessful. Rather, it would appear that the capacity to respond to low serum is an unstable property lost after a few generations in low serum. The loss of responsiveness shows parallels with “cellular senescence” and could conceivably result from decay of the platelet‐derived growth factor‐induced state of “competence.” But regardless of why some cells respond to low serum while others do not, it is clear that the kinetics of entry into S phase after serum stimulation of quiescent 3T3 cells are not strictly first‐order, since the labelling index plateaus after roughly 3 days at values substantially below 100%. As such, the kinetics, though not contradicting the transition probability model, cannot be taken to support it as was previously thought.
Cell cycle regulation by environmental pH
Authors: Taylor Ian W. , Hodson Pamela J. 
Published: February 2005

AbstractPurified populations of quiescent human tumour cells were isolated from plateau phase cultures of PMC‐22 cells by centrifugal elutriation. Dilution into fresh medium resulted in these quiescent cells entering S phase exponentially with a t1/2 of 12 hr, after a 18‐20‐hr lag period during which cellular RNA content increased. Subsequent studies showed that recruitment of quiescent cells into the cell cycle could be regulated by extracellular pH. When exponentially growing PMC‐22 cells were exposed to acidic extracellular pH levels, three growth patterns were observed: (1) Normal growth between pH 7.2 to pH 6.8; (2) A reduction in growth rate associated with accumulation of cells with a G1 DNA content between pH 6.7 and 6.4 (this was also shown to occur in a number of other tumour cell lines); (3) Non‐cell‐cycle‐phase‐specific arrest of growth at pH levels less than 6.3. Further studies with purified quiescent cell populations showed the possible existence of a pH‐dependent restriction point in the G1 phase of these tumour cells. The implications of these observations to tumour biology are discussed.
Phorbol esters inhibit the binding of low‐density lipoproteins (LDL) to U‐937 monocytelike cells
Authors: Rouis M. , Goldstein S. , Thomopoulos P. , Berthelier M. , Hervy C. , Testa U. 
Published: February 2005

AbstractThe present study demonstrates that U‐937 monocytelike human cells possess specific LDL receptors. 125I‐LDL binds at 4°C on the cell surface. The bound molecules are releasable by heparin. The reaction requires Ca2+ and the binding sites are sensitive to proteolysis. Unlabeled LDL compete with 125I‐LDL, whereas HDL are ineffective. At 37°C, LDL are internalized and degraded by a chloroquine‐sensitive pathway. Tumor‐promoting phorbol esters inhibit the binding of 125I‐LDL to its receptor on U‐937 cells. This inhibition exhibits temperature, time, and concentration dependence. At 37°C, inhibition is 50% at 5 × 10−9 M of TPA. After removal of phorbol esters, treated cells recover their 125I‐LDL‐binding activity in 60 min. The inhibitory activities of various phorbol esters are proportional to their tumor‐promoting activities. Inhibition appears to be due to a reduction in the number of available LDL receptors rather than a decrease in receptor affinity.
Correlation between trypsin binding to a specific receptor and prostacyclin production in cultured vascular endothelial cells
Authors: Savion Naphtali , Naveh‐Floman Nava 
Published: February 2005

AbstractThe correlation between the binding and processing of trypsin and its effect on prostacyclin (PGI2) production in cultured adult bovine aortic endothelial (ABAE) cells was studied. ABAE cells demonstrated an ability to produce PGI2 in a dose‐response manner to trypsin at the range of 0.1–2.0 μg/ml with a saturation at a concentration of 1 μg/ml; Likewise, 125I‐trypsin binding to the cultured cells increased in a dose‐response way and reached saturation at a concentration of about 1 μg/ml; 125I‐trypsin was bound to a specific high‐affinity cell‐surface receptor with a dissociation constant (Kd) of 1.5 × 10−8 M and each of the confluent ABAE cells has about 1.2 × 105 such receptors sites. The cell‐surface receptor for trypsin displayed specific characteristics and an excess amount of unlabeled trypsin successfully abolished 125I‐trypsin binding while thrombin in excess failed to compete for 125I‐trypsin binding. Only a small fraction of the cell‐surface‐bound 125I‐trypsin was internalized and subsequently degraded by ABAE cells as compared to the process of 125I‐trypsin internalization by human skin fibroblasts (HSF). This study demonstrated that the stimulatory effect of trypsin on prostacyclin production and release by ABAE cells might be mediated by a specific cell‐surface receptor for trypsin on these cells distinct from the thrombin receptor.
Production and characterization of interferon from endothelial cells
Authors: Einhorn Stefan , Vlodavsky Israel , Fuks Zvi , Eldor Amiram , Panet Amos 
Published: February 2005

AbstractThe capacity of cultured bovine aortic, capillary, and corneal endothelial cells as well as of human umbilical cord endothelial cells to produce interferon (IFN) was investigated. The endothelial cells of the two species produced significant amounts of IFN in response to various viruses and poly (I) poly (C). The IFN produced by human umbilical cord endothelial cells was a mixture of α‐ and β‐IFN, as determined by neutralization with antibodies directed against these two types of IFNs as well as by measuring the antiviral activity on heterologous cells. Bovine endothelial cells also produced a mixture of at least two IFN subspecies, one of them labile at pH 2 and active on human cells and the other stable at pH 2 and inactive on human cells.
Induction of stress proteins in chicken embryo cells by low‐level zinc contamination in amino acid‐free media
Authors: Whelan Sandra A. , Hightower Lawrence E. 
Published: February 2005

AbstractIt has been reported that chicken embryo cells deprived of exogenous amino acids for 4 hours synthesize stress (heat‐shock) proteins. Herein, we show that amino acid deprivation is not sufficient to cause induction of stress proteins. Zinc contaminating a component of commercial cell culture medium used to prepare amino acid‐free medium was an inducer in our cultures. In the absence of exogenous amino acids, the concentration of zinc ions needed for half‐maximal induction of stress proteins was an order of magnitude lower than the dose required for cells in complete medium. Histidine and cystine, which have high affinities for zinc ions, were the amino acids most effective in blocking the induction of stress proteins by zinc. Problems posed by heavy metal ions in culture media and biologic fluids for searches for in vivo inducers of the cellular stress (heat shock) response are discussed.
Induction of endoreduplication in temperature‐sensitive mutants of rat 3Y1 fibroblasts
Authors: Yamada Koji , Kimura Genki 
Published: February 2005

AbstractFour temperature‐sensitive mutants of rat 3Y1 fibroblasts belonging to separate complementation groups (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) are arrested mainly with a 2C DNA content, when cells proliferating at 33.8°C are shifted up to 39.8°C (Ohno et al., 1984). Zaitsu and Kimura (submitted for publication) showed that 3Y1tsF121 cells synchronized in the early S phase were arrested with a 4C DNA content at 39.8°C. We studied the traverse through the S and G2 phases at 39.8°C in the four ts mutants synchronized at the early S phase and found that 3Y1tsG125 and 3Y1tsH203 cells were arrested with a 4C DNA content as 3Y1tsF121, while 3Y1tsD123 cells went through S and G2 phases and underwent mitosis. When 3Y1tsF121 and 3Y1tsG125 mutants arrested at 39.8°C were shifted down to 33.8°C, a substantial fraction of the cells with a 4C DNA content started, with a certain lag period, DNA synthesis without intervening mitosis and underwent the first mitosis with a lag period similar to that in the cells arrested with a 2C DNA content. The tetraploid cells thus generated had a proliferating ability lower than that of diploid cells.
Lineage specific receptors used to identify a growth factor for developmentally early hemopoietic cells: Assay of hemopoietin‐2
Authors: Bartelmez Stephen H. , Sacca Rosalba , Stanley E. Richard 
Published: February 2005

AbstractA new approach, based on the occurrence of receptors for the mononuclear phagocyte lineage specific hemopoietic growth factor (HGF) colony stimulating ractor‐1 (CSF‐1) on developmentally early multipotent cells, is utilized to detect and assay rapidly another HGF, hemopoietin‐2. This method is also used to determine the relative maturity of hemopoietin‐2 target cells, to investigate synergism between hemopoietin‐2 and CSF‐1, and to measure CSF‐1 receptor levels on maturing cells. While the target cell specificities of hemopoitin‐2 and CSF‐1 overlap, hemopoietin‐2 causes the appearance of developmentally earlier 125I‐CSF‐1 binding cells de novo in the absence of CSF‐1. Increased CSF‐1 receptor densities are observed on cells incubated with either HGF, consistent with acquisition of the capacity for increased expression of the receptor by mononuclear phagocyte progenitor cells just prior to their differentiation to adherent mononuclear phagocytes. Together, both HGFs have a synergistic effect on the generation of 125I‐CSF‐1 binding cells with elevated CSF‐1 receptor densities. Preliminary characterization of hemopoietin‐2 from medium conditioned by WEHI‐3 cells indicates that it is very similar to, if not identical with, interleukin‐3 (IL‐3) and the HGF(s) acting on multipotential cells and cells giving rise to erythroid cells, granulocytes, mononuclear phagocytes, and megakaryocytes. Purified IL‐3 was shown to possess hemopoietin‐2 activity.
FACS analysis of a hyperthermia‐induced alteration in Hoechst 33342 permeability and direct measurement of its relationship to cell survival
Authors: Rice Glenn C. , Gray Joe W. , Dewey William C. 
Published: February 2005

AbstractHeat‐induced alterations in CHO‐10B cell Hoechst 33342 (Ho342) permeability in vitro were analyzed by flow cytometry. Immediately after 45.5°C heating, uptake was decreased in a dose‐dependent manner with cytotoxicity. Kinetic analysis indicated that a treatment that reduced cell survival to approximately 10%, reduced the maximal velocity, Vmax, to 53% of control and increased the dissociation constant, Km, to 156% of control. Also, little change in Ho342 efflux was found to occur from control up to 90 min after heating. Upon incubation at 37°C after the heat treatment from 1 to 24 hr (depending on the severity of the dose) diffuse heterogeneity of Ho342 staining developed which was not evident immediately after heating. The altered staining was not due to the presence of trypan blue staining cells. Membrane permeabilization and nuclei isolation studies indicated that the lesion responsible was most likely a plasma membrane event. Induction of the heterogenous staining was not inhibited by either actinomycin D or hydroxyurea but was inhibited by incubation at 4°C. An inverse correlation existed between Ho342 permeability and clonogenicity, with nearly a 10‐fold difference in survival between the high and low fluorescence intensity sorted cells. Also, larger fractions of heatsensitive S and G2M‐phase cells were found in the highly fluorescent sorted fractions. These results are discussed in terms of the putative molecular events that may be involved in hyperthermic modulation of Ho342 permeability.
Uptake of transferrin and iron by cultured rat placental cells
Authors: McArdle H. J. , Douglas A. J. , Morgan E. H. 
Published: February 2005

AbstractThis paper describes a method for the culture of rat placental cells. The method involved separation of the basal layer from the labyrinth and sequential digestion of the cells. The cells were demonstrated not to be fibroblasts and are described in terms of their appearance under the light and electron microscopes. Transferrin and iron uptake by the cells was examined and compared with results achieved using other methods of study. The results showed that transferrin bound to receptors on the cell surface and that the transferrin, once bound, was taken into the cell. Only this internalized transferrin was capable of donating iron to the cells. The iron was accumulated within the cells and did not appear to be released to the incubation medium. The apparent dissociation constant (Ka) for transferrin was found to be 6.96 × 106 M−1, a value similar to that described by earlier workers. The placental cells had 3.4 × 1011 binding sites/μg DNA, equivalent to approximately 1 × 106 sites/cell. From these data, and from the rate of accumulation of iron by the cells, the receptor turnover time was estimated as being between 5 and 10 min.
Regulation of proliferation of bovine aortic endothelial cells, smooth muscle cells, and adventitial fibroblasts in collagen lattices
Authors: Weinberg Crispin B. , Bell Eugene 
Published: February 2005

AbstractWe compared the proliferation of bovine aortic cells grown in collagen lattices. Smooth muscle cells continued to divide for 2 weeks while adventitial fibroblasts ceased to divide after 4–5 days. Endothelial cells did not proliferate within an untreated collagen lattice; however, if the lattice was covered with culture medium, endothelial cells populated its surface and proliferated to form a monolayer. We also found that both smooth muscle cells and endothelial cells, like fibroblasts, are able to contract a collagen lattice to a small fraction of its original volume, although endothelial cells are able to do so only if the lattice is covered with culture medium.
Calcium regulation of phosphatidyl inositol turnover in macrophage activation by formyl peptides
Authors: Holian Andrij , Stickle Douglas F. 
Published: February 2005

AbstractStimulation by the tripeptide N‐formyl norleucyl leucyl phenylalanine (FNLLP) of the guinea pig alveolar macrophage gives rise to transient production of superoxide anion (O2−). Components of the phosphatidyl inositol (PI) cycle (phosphatidic acid) (PA), phosphatidyl inositol‐4,5‐bisphosphate (TPI) and phosphatidyl inositol‐4‐phosphate (DPI) were monitored using 32P in order to examine the possible association of this cycle with the FNLLP‐stimulated production of O2−. Macrophage stimulation by FNLLP led to an increased flux of metabolites through the PI cycle. The level of 32P label in both TPI and DPI rapidly decreased upon exposure to FNLLP, followed by a 5‐min period during which the 32P label in TPI and DPI approached prestimulated levels. During this period, there was a fivefold increase in 32P‐PA. It is suggested that diacylglycerol (DAG) is the O2− production. The importance of continued cycling of PI in the stimulated mechanism is demonstrated by the inhibition by LiCl of the extent, but not the initial rate, of both O2− production and the formation of 32P‐PA upon peptide stimulation after 1‐h preincuexamined. It has previously been demonstrated that intracellular availability of calcium can influence the rate and extent of O2− production. In cells preloaded with quin‐2, which acts as a high‐affinity sink for calcium in the cytosol, the initial rate of FNLLP‐stimulated O2− production is inhibited in low (10 μM) extracellular calcium medium. High extracellular calcium (1 mM) completely reverses this inhibition and also significantly extends the time course of O2− production in both quin‐2 and control cells (Stickle et al., 1984). In parallel with these effects on O2− production, varying calcium conditions is demonstrated to influence the rate and extent of PA formation. These same calcium conditions were found to have little or no effect on the initial unstimulated levels of TPI, DPI, and PA. These results indicate that the influence of an intracellular pool of calcium on O2− production may be via its influence on stimulated PI turnover.
The effect of ionophores and related agents on the induction of doming in a rat mammary epithelial cell line
Authors: Paterson Frieda C. , Graham John M. , Rudland Philip S. 
Published: February 2005

AbstractAddition of dimethyl sulfoxide (DMSO) and the mammotropic hormones prolactin, hydrocortisone, insulin, and estradiol to confluent cultures of the epithelial cell line Rat Mammary (Rama) 25 increases dramatically the formation of domes in the cell monolayer after 48–72 hr. Associated with the increase in doming is an increase of 24% in the activity of the Na+/K+ ATPase. Both Ca2+ (A23187) and Na+ (monensin, gramicidin J, melittin) ionophores can replace DMSO in inducing domes whilst the K+ ionophore valinomycin inhibits doming. However, there are no synergistic nor additive effects, respectively, with suboptimal or optimal concentrations of A23187 and melittin together. Ouabain, at concentrations which inhibit the Na/K ATPase in vitro, and amiloride, at concentrations reported to inhibit the passive transport of Na+, both inhibit completely the formation of domes induced by DMSO, A23187, and melittin. EGTA, however, inhibits only the induction of doming by DMSO and A23187; it is without effect with melittin. A23187 and melittin induce the major polypeptide changes that occur in doming cultures with DMSO, and most of these changes are also inhibited with ouabain. It is suggested that one possible interpretation of the findings is that the induction of doming by DMSO in Rama 25 cells occurs by means of sequential increases in Ca2+ and Na+ influxes into the cell, and that the increased intracellular concentration of Na+ so produced stimulates the Na+/K+ ATPase, with a net effect of pumping liquid beneath the cellular monolayer.