bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of HgCl2 to evaluate the cosubstrate: Amino acid transport stoichiometry in ehrlich ascites tumor cells
Authors: David Dawson W. , Robinson Susan C. , Smith Thomas C. 
Published: February 2005

AbstractRecent investigations have indicated that cellular rheogenic properties may interfere with the correct estimation of Na+ and amino transport stoichiometry. We have reevaluated the stoichiometry of Na+ and α‐aminoisobutyric acid (α‐AIB) cotransport in Ehrlich ascites tumor cells depleted of Na+ and ATP by incubation in Na+ ‐free HEPES‐buffered medium (pH 7.2) containing 160 mM K+ and 2.5 μM valinomycin. Transfer of the cells to a medium with 10 mM 22Na+, 10 mM 3H‐AIB, and 150 mM K+ resulted in an enhancement of Na+ flux above basal levels, which represents 0.6 of the AIB uptake. Under these conditions the membrane potential, −7.0 ± 0.1 mV (SEM), does not change with the addition of AIB, −7.3 ± 0.6 mV (SEM). HgCl2 (10 m̈M) added to the medium inhibited AIB flux and AIB‐stimulated Na+ flux by 45–50% but did not change the coupling ratio. HgCl2 (10 m̈M) does not inhibit the basal Na+ flux nor does it affect cellular Na+ or K+ content. In physiological medium cotransport is electrogenic. The membrane potential of Ehrlich cells in physiological medium is −22.3 ± 0.8 mV (SEM) and depolarizes to −16.7 ± 0.7 mV (SEM) upon addition of AIB. Under these conditions the coupling ratio was highly variable but the ratio of codepression is 0.90 ± 0.02 (SEM) in the presence of HgCl2 (10 m̈M). These results are consistent with a model (Smith and Robinson, 1981) in which the stoichiometry is one cosubstrate molecule per molecule of α‐AIB. We suggest that H+ provides the alternative cosubstrate in this low Na+ environment and that in high Na+ medium the Na+ :AIB stoichiometry approaches 1:1.
Coordinate secretion of rat and mouse albumin by mouse hepatoma × rat hepatoma hybrid cells directly reflects the intracellular concentration of the corresponding mRNAs
Authors: Sellem Carole H. , Cassio Doris , Sala‐Trepat Joséa M. , Weiss Mary C. 
Published: February 2005

AbstractThe ratio of mouse to rat albumin secreted by mouse hepatoma × rat hepatoma hybrid cells is constant (of the order of 5.0) irrespective of the total amounts produced. The present results establish for seven independent hybrid clones that the coordination in the ratio of mouse to rat product applies also at the level of accumulation of albumin mRNAs of the two species. The interpretation that coordinate synthesis reflects coordinate transcription of the relevant genes is thus reinforced.
Comparative biochemical and cytochemical studies on superoxide and peroxide in mouse macrophages
Authors: Badwey J. A. , Robinson J. M. , Lazdins J. K. , Briggs R. T. , Karnovsky M. J. , Karnovsky M. L. 
Published: February 2005

AbstractMaximal rates of superoxide (O) release, and the cytochemical locales of peroxide staining in resident, elicited, and activated macrophages have been determined. Macrophages elicited into the peritoneum with either casein (1.2% w/v) or proteose‐peptone (10.0% w/v) release about twice as much O as macrophages activated by infection of the animals with either Listeria monocytogenes, or Bacille Calmette‐Guerin (BCG) followed by immune boosting with Purified Protein Derivative (PPD) (i.e., about 35 vs. 14–18 nmol O/min/107 cells). Macrophages elicited with thioglycollate (3.0% w/v) and resident macrophages produce negligible amounts of O upon stimulation with PMA. These data are compared with those reported by other investigators who used different procedures. A cytochemical procedure for localizing peroxide has been modified for use with murine macrophages. No production of H2O2 by macrophages is detected cytochemically in the absence of stimulation. Upon exposure to PMA, resident macrophages are still largely unresponsive. Approximately 20% of the casein elicited macrophages and BCG‐PPD activated macrophages exhibit H2O2 staining, which is largely restricted to the cytoplasmic vesicles and channels induced by PMA in these cells. The only exception to this staining pattern is a small population (about 2%) of activated macrophages which exhibits H2O2 staining in the cytoplasmic vesicles and channels and on the plasmalemma as well.
Properties of growth hormone receptors in relation to the adipose conversion of 3T3 cells
Authors: Nixon Tracy , Green Howard 
Published: February 2005

AbstractCultured preadipose 3T3 cells undergo a process of differentiation in which they convert to adipose cells. Growth hormone promotes this conversion. Since 3T3 sublines vary in their susceptibility to adipose conversion, it was of interest to examine the properties of the growth hormone receptors in relation to that susceptibility. It was found that preadipose 3T3‐F442A cells, which are able to convert to adipose cells with high frequency, are able to bind about 104 growth hormone molecules per cell with Kd ∼︁ 10−9M. After adipose conversion, no appreciable change in hormone binding was detected. The binding of growth hormone to 3T3‐C2 cells (a line virtually insusceptible to adipose conversion) was indistinguishable from that to 3T3‐F442A cells. Internalization and degradation of the hormone were also similar in the two cell lines. Susceptibility to adipose conversion is therefore not determined by the relative ability of the cells to bind or degrade the hormone, but must instead depend on some response, as yet unidentified, that follows binding of the hormone.
The formation of capillary‐like tubes by calf aortic endothelial cells grown in vitro
Authors: Feder J. , Marasa J. C. , Olander J. V. 
Published: February 2005

AbstractCloned, large vessel endothelial cells derived from fetal bovine and bovine calf aortas formed three‐dimensional structures in vitro without tumor‐conditioned medium or special substrata. Transmission electron microscopy showed the structures to be hollow tubes composed of typical endothelial cells with overlapping and interdigitating cytoplasmic processes typical of those seen in in vivo capillaries. The putative lumen of these tubes generally contained abundant electron‐dense fibrous material, which by ruthenium red and indirect immunofluorescent staining appeared to be extracellular matrix. This suggests that the endothelial cell orientation in the tubes is the reverse of that normally found in in vivo vessels.
The role of the mannose/N‐acetylglucosamine receptor in the pinocytosis of horseradish peroxidase by mouse peritoneal macrophages
Authors: Sung Sun‐Sang J. , Nelson Rolf S. , Silverstein Samuel C. 
Published: February 2005

AbstractSaccharomyces cerevisiae mannan inhibits the pinocytosis of horseradish peroxidase (HRP) by resident, thioglycollate‐, proteose peptone‐, and Co‐rynebacterium parvum‐elicited macrophages from 30 to 70% when 1 mg/ml HRP is used, and 65 to 87% when 250 μg/ml HRP is used. In contrast, HRP uptake by J774 cells, a macrophage cell line reported to have little mannose receptor activity, is inhibited only about 25% by mannan. HRP uptake by resident and thioglycollate‐elicited (thio) macrophages is also inhibited 34 and 66% by addition of EGTA to the medium and 55 and 79% by trypsin treatment of the macrophages, respectively. The inhibitory effect of EGTA can be reversed by 1 mM excess Ca2+. High extracellular concentrations of Ca2+, in the range of 10–20 mM, however, inhibit pinocytosis in resident macrophages by about 50%. Sucrose uptake by resident macrophages is not appreciably affected by mannan. These results support the hypothesis that HRP uptake is mediated by the macrophage mannose/N‐acetylgluco‐samine receptor. PMA stimulates fluid‐phase pinocytosis of HRP by thio‐macrophages but does not affect receptor‐mediated uptake of HRP, while the combination of adenosine, homocysteine, and erythro‐9‐(2‐hydroxy‐3‐nonyl) adenine (EHNA) selectively inhibits bulk‐phase uptake by thio macrophages.
Calcium‐dependent activation of lymphocytes by ionophore, A23187, and a phorbol ester tumor promoter
Authors: Mastro Andrea M. , Smith M. C. 
Published: February 2005

AbstractThe phorbol ester tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) and the calcium ionophore, A23187, have similar effects on many different cells. For example, both show mitogenic and comitogenic activities for lymphocytes. It had been suggested that some of TPA's effects are due to its ability to act as a calcium ionophore. In order to test this idea, we compared the ability of TPA and ionophore to synergize with concanavalin A (Con A) in a two‐phase system of lymphocyte mitogenesis. We found that ionophore was most comitogenic with Con A when present in the early phase of stimulation. TPA was only comitogenic when present in the late phase, lonophore and TPA could not replace one another in the system. However, both ionophore and TPA together could replace Con A and stimulate DNA synthesis when they were presented to the cells in the sequential order of ionophore followed by TPA. Both compounds required the presence of external calcium to be effective.
Metabolic characteristics of cells cultured from human umbilical blood vessels: Comparison with 3T3 fibroblasts
Authors: Bruttig Stephen P. , Joyner William L. 
Published: February 2005

AbstractLittle metabolic information is available for cells cultured from umbilical vascular tissue. These studies were undertaken to compare the metabolism of cells isolated from human umbilical arteries and veins with that of umbilical vascular segments. These studies also compared umbilical vascular cells to standard fibroblast preparations. Oxygen consumption by umbilical venous cells or tissues was greater than that for either arterial cells or tissues. Cellular adenosine triphosphate (ATP) content was greater in umbilical venous than arterial cells. However, an oxidation‐phosphorylation ratio (R) was constant for either arterial or venous cells. Oxygen consumption by vascular cells was greater than that by nonvascular cells, as was cellular ATP content. R for nonvascular cells was much greater than that for vascular cells, indicating loose coupling between oxygen consumption and cellular ATP content. Finally, cellular oxygen consumption was dependent upon cell density, and upon media serum content in vascular endothelial cells. We conclude therefore that the metabolism of umbilical vascular cells in culture reflects that of the parent tissue but is different from that of either vascular or nonvascular fibroblasts.
Tumor‐promoting phorbol esters inhibit the binding of colony‐stimulating factor (CSF‐1) to murine peritoneal exudate macrophages
Authors: Chen Ben D.‐M. , Lin Hsiu‐San , Hsu Shin 
Published: February 2005

AbstractL‐cell colony‐stimulating factor (CSF‐1) is a sialoglycoprotein of molecular weight 70,000 daltons that specifically stimulates macrophage colony formation by single committed cells from normal mouse bone marrow and by various classes of more differentiated tissue‐derived mononuclear phagocyte colony‐forming cells (Stanley et al., 1978). CSF‐1 interacts with target cells by direct and specific binding to membrane receptors (CSF‐1 receptors) that are present only on cells of the mononuclear phagocyte series and their precursors. We studied the effect of tumor‐promoting phorbol esters on the binding of 125I‐labeled CSF‐1 (125‐CSF‐1) to murine peritoneal exudate macrophages (PEM). Biologically active TPA (12‐O‐tetradecanoyl phorbol‐13‐acetate) inhibits the binding of 125I‐CSF‐1 to its receptor on PEM. This inhibition exhibits temperature, time, and concentration dependence. At 37°C, maximum inhibition occurred at about 10−7 M; inhibition was 50% at 5 × 10−9 M. At 0°C, the inhibitory activity of TPA is diminished. The action of TPA on PEM is transient. Treated cells recover their 125I‐CSF‐1‐binding activity whether TPA is later removed or not. The process of recovering CSF‐1‐binding activity is completely blocked by the addition of cycloheximide. When several phorbol derivatives were tested for their inhibitory activities, only biologically active phorbol esters were found to possess such activities. Furthermore, the inhibitory activities of various phorbol esters are proportional to their tumor‐promoting activities. Inhibition appears to be due to a reduction in the total number of available CSF‐1 receptors rather than a decrease in receptor affinity.
Characteristics of an amiloride‐sensitive sodium entry pathway in cultured rodent glial and neuroblastoma cells
Authors: Benos Dale J. , Sapirstein Victor S. 
Published: February 2005

AbstractWe have studied the induction of an amiloride‐sensitive sodium influx into C6 glioma, NIE, and NB2A neuroblastoma cell lines. In late log phase, cells grown continuously in the presence of 10% fetal calf serum showed Na+ influxes of approximately 25–30 nmol/mg protein min; < 5% of this flux was inhibited by amiloride. Removal of serum for 24 h caused a decrease in the total Na+ influx to 15–20 nmol/mg protein/min. Upon readdition of serum to the incubation medium, there was an increase in total Na+ influx, depending on the cell type, of 20–400% within 2 min. This increment in Na+ influx represented an increase in amiloride‐sensitive Na+ transport with an apparent K′, of 0.4 mM. By adding serum back at various times after serum deprivation, it was determined that 4 h was required to observe a detectable increase in the amiloride‐sensitive Na+ flux. Thus, serum removal results in the induction of the amiloride transport system which, however, remains latent until the reintroduction of serum to the medium. Addition of 5 μg/ml of cycloheximide blocked the increase in Na+ transport, indicating that de novo protein synthesis mediated this serum deprivation–induced increase in Na+ transport. Moreover, inhibition of de novo lipid synthesis by 0.1 mM fenfluramine also blocked the induction of this transport activity, suggesting that a coordinated synthesis of lipid and protein is required for the expression of this sodium transport site. We have also found that this serum stimulated Na+ influx did not saturate with Na+ concentration, up to 140 mM. Also, among commonly used inhibitors of passive Na+ entry into epithelial tissues, only amiloride was capable of inhibiting this transport system in these neural cell lines.
Adenosine metabolism in wild‐type and enzyme‐deficient variants of Chinese hamster ovary and Novikoff rat hepatoma cells
Authors: Plagemann Peter G. W. , Wohlhueter Robert M. 
Published: February 2005

AbstractVariants of Chinese hamster ovary and Novikoff rat hepatoma cells resistant to tubercidin and 2,5‐diaminopurine, or to both drugs, were isolated, and their ability to convert adenosine and various adenosine analogs to nucleotides was compared to that of wild‐type cells, both in intact cells and cell‐free extracts. Adenosine deamination, and thus its conversion to nucleotides via inosine‐hypoxanthine‐inosine monophosphate, was inhibited by pretreatment of the cells or cell extracts with 2‐deoxycoformycin. Cell‐free extracts of the tubercidin‐resistant variants, as well as of two adenosine‐resistant mutants of Chinese hamster ovary cells, phosphorylated adenosine, tubercidin, pyrazofurin, or tricyclic nucleoside in the presence of ATP at < 1% of the rate of extracts of wild‐type cells. However, addition of phosphoribosyl pyrophosphate stimulated the conversion of adenosine to nucleotides 40‐fold. Similarly, intact adenosine kinase‐deficient cells failed to phosphorylate the adenosine analogs, but still converted adenosine to nucleotides at 5–10% the rate observed with wild‐type cells. Phosphorylation of adenosine and tubercidin in wild‐type cells was inhibited by substrate at concentration above 5–10 μM. In contrast, the rate of conversion of adenosine to nucleotides by adenosine kinase‐deficient cells increased linearly up to a concentration of 400 μM adenosine, with the consequence that, at this concentration, these cells took up adenosine almost as rapidly as wild‐type cells. Adenosine uptake by these kinase‐deficient cells was inhibited by adenine and 5′‐deoxyadenosine, and was largely abolished in mutants devoid also of adenine phosphoribosyltransferase. We conclude that adenosine is converted to nucleotides in adenosine kinase‐deficient cells via adenine. Indirect evidence implicates 5′‐methylthioadenosine phosphorylase as the enzyme responsible for the degradation of adenosine to adenine.
Adenosine and tubercidin binding and transport in Chinese hamster ovary and Novikoff rat hepatoma cells
Authors: Plagemann Peter G. W. , Wohlhueter Robert M. 
Published: February 2005

AbstractThe uptake of adenosine and tubercidin by control and ATP‐deleted wild‐type and adenosine kinase‐deficient cells was measured by rapid kinetic techniques. Adenosine deamination was inhibited by pretreatment with 2‐deoxy‐coformycin. Control wild‐type cells phosphorylated adenosine so rapidly that the kinetics of transport per se could not be assessed unambiguously. ATP depletion and adenosine kinase deficiency did not abolish the conversion of adenosine to nucleotides, but reduced it to such an extent that initial velocities of uptake could be safely construed as transport velocities in both zerotrans and equilibrium exchange modes. The same was true for tubercidin, which was not phosphorylated in adenosine kinase‐deficient cells. It accumulated intracellularly, however, to concentrations 50 to 120% higher than those in the extracellular space, apparently due to binding to some intracellular component(s). Binding was not saturated up to a concentration of 200 μM, but seemed to be slow relative to transport. Fits of appropriate integrated rate equations based on the simple carrier model to uptake time courses obtained under these conditions yielded Michaelis‐Menten constants for adenosine and tubercidin transport of 100 to 200 μM and maximum velocities of 10 to 30 pmol/μl cell H2O ċ sec, whereas the rate of intracellular phosphorylation was maximal at concentrations between 2 and 8 μM. The first‐order rate constant (Vmax/Km) for adenosine phosphorylation, however, seemed to be appreciably higher than that for its transport. This indicates that at physiological concentrations, which fall in the first‐order range for both processes, adenosine trapping is very efficient. Adenosine, tubercidin, tricyclic nucleoside, 2′‐deoxyadenosine, and 3′‐deoxyadenosine all inhibited uridine and thymidine transport to about the same extent, whereas pyrazofurin was signficantly less effective.
Efflux of 45CA2+ from human fibroblasts in response to serum or growth factors
Authors: Owen Nancy E. , Villereal Mitchel L. 
Published: February 2005

AbstractPrevious studies have indicated that intracellular Ca2+is involved in fetal bovine serum (FBS)‐ or growth factor (GF)‐stimulated Na+ influx in human foreskin fibroblasts (HSWP). In the present study, 45Ca2+ efflux from serum‐deprived HSWP cells was measured in response to 10% FBS or GF [lys‐bradykinin, vasopressin, epidermal growth factor, and insulin]. Efflux data were analyzed using a computer program and the best fit indicated the presence of three Ca2+ compartments: a compartment (C1) with a very fast turnover rate, one (C2) with a fast turnover rate, and one (C3) with a slow turnover rate. When serum‐deprived cells were treated with 10% FBS, efflux from C2 and C3 increased significantly (p>0.05). Similar effects on efflux were observed when serum‐deprived cells were treated with individual GFs. Combination of the four GFs produced a higher stimulation than any single factor and a response that was equal to that for FBS. On the other hand, when cells were serum‐treated in the presence of the intracellular Ca2+ antagonist, 8‐(N‐N, diethylamino)‐octyl 3,4,5‐trimethoxybenzoate (TMB‐8), 45Ca2+ efflux from C2 was substantially reduced. Finally, when cells were treated with the Na+ transport inhibitor amiloride, there was no significant effect on serum‐stimulated Ca2+ efflux. These results are consistent with a FBS‐ or GF‐induced mobilization of Ca2+ that can be blocked by intracellular Ca2+ antagonists, and support the hypothesis that the action of these agents on Na+ influx may be via their effects on intracellular Ca2+.
Growth stimulatory precipitates of CA2+ and pyrophosphate
Authors: Bowen‐Pope D. F. , Rubin H. 
Published: February 2005

AbstractInorganic pyrophosphate (PPi) forms an insoluble precipitate with calcium in growth medium when its concentration exceeds about 0.1 mM. This PPi precipitate can reproduce the effects of 10% calf serum on all cell processes examined in Balb/c 3T3 cells, including hexose uptake and metabolism to lactate, 3H‐uridine, and 3H‐choline uptake, and the incorporation of 3H‐leucine and 3H‐thymidine into trichloroacetic acid (TCA)‐insoluble material. Concentrations of PPi insufficient to form a precipitate are without effect on cell metabolism. The precipitates are most effective when prepared with concentrations of PPi just sufficient to result in precipitate formation and become considerably less effective as the PPi concentration increases, even though the quantity of precipitate formed continues to increase with PPi concentration up to 1 mM PPi. Precipitates formed at low PPi concentrations consist largely of Ca2+ (81% of cations). PPi (77% of anions), and Pi (23% of anions). Precipitates formed with higher concentrations of PPi contain proportionately less Ca2+ and Pi and more monovalent cations and PPi. We have distinguished cell surface‐bound PPi from intracellular PPi by differential extraction. The quantity of surface‐bound PPi increases sharply when the PPi concentration reaches the point of precipitate formation. If the precipitate is prevented from binding to the cell surface by inverting monolayer cultures in precipitate‐containing medium, the cells are not stimulated. These findings suggest that the binding of PPi precipitate to the cell surface is involved in the stimulation of cell metabolism by PPi. PPi precipitates do not absorb serum mitogens or inhibitors from the culture medium, nor do they affect the binding of 125I‐platelet‐derived growth factor to its specific cell‐surface receptor, suggesting that PPi precipitates do not act directly through either of these mitogen‐receptor systems. In analogy to cell stimulation by epidermal growth factor and by antigens, we suggest that PPi may be active only in the form of a precipitate because multivalent binding of receptors with formation of clusters is required for stimulation. The inhibitory effects of high concentrations of PPi may be due to interference by free PPi with formation of active receptor clusters.
Effect of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) on the growth inhibitory and increased phosphatidylinositol (PI) responses induced by epidermal growth factor (EGF) in A431 cells
Authors: Smith Kathryn B. , Losonczy Ilona , Sahai Atul , Pannerselvam Mounanandham , Fehnel Paula , Salomon David S. 
Published: February 2005

AbstractEpidermal growth factor (EGP) inhibited the growth of A431 human epidermoid carcinoma cells. The tumor promoting, phorbol ester, 12‐O‐tetradeca‐noylphorbol‐13‐acetate (TPA) also retarded A431 cell growth. Addition of both TPA and ECF inhibited cell growth in an additive or synergistic manner depending upon the initial plating density of the cultures. EGF increased the production of diacylglycerol (60–70%) and stimulated the synthesis of phosphatidylinositol (PI) from 3H‐inositol (three‐ to fourfold increase). Both of these responses were attenuated in the presence of TPA. TPA alone stimulated the production of diacylglycerol (DG) but had little effect on PI synthesis. The biological effect of TPA appeared to be mediated by the presence of a high‐affinity receptor for phorbol esters on A431 cells. Moreover, the binding of 125I‐EGF to A431 cells was unaffected by TPA, suggesting that the antagonistic effects of TPA were occurring distal to the EGF receptor. These findings also indicated that although TPA and EGF both inhibited A431 cell growth, this effect could be dissociated from changes in PI synthesis but may be dependent upon transient changes in DG production.