bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induction of 86Rb Fluxes by Ca2+ and volume changes in thymocytes and their isolated membranes
Authors: Grinstein S. , Cohen S. , Sarkadi B. , Rothstein A. 
Published: February 2005

AbstractCell swelling and elevated intracellular Ca2+ increase K+ permeability in lymphocytes. Experiments were performed to test whether these effects can also be elicited in isolated plasma membrane vesicles. Rabbit thymocytes, used as a source of membrane vesicles, were found to regain their volume after swelling in hypotonic, low‐K+ media. This regulatory volume decrease (RVD) was inhibited by quinine and trifluoperazine, but not affected by ouabain. Both efflux and uptake of K+ (86Rb) were stimulated by hypotonicity. Addition of A23187 plus Ca2+ also increased 86Rb fluxes. Ca2+ ‐ and volume‐induced 86Rb fluxes were also studied in isolated membranes. A plasma membrane‐rich vesicle fraction, enriched over 11‐fold in 5′‐nucleotidase, was isolated from thymocytes. The vesicles were about 35% inside‐out and trapped 86Rb in an osmotically active compartment of ∼1.3 μl/mg protein. Equilibrium exchange fluxes of 86Rb in the vesicles were unaffected by Ca2+ with or without A23187. Calmodulin had no effect on 86Rb permeability but stimulated ATP‐dependent Ca2+ accumulation. Hypotonic swelling increased both uptake and efflux of 86Rb from vesicles. However, this increase was not blocked by either quinine or trifluoperazine, was not specific for K+ (86Rb), and is probably unrelated to RVD. It is concluded that components essential for the volume‐ and Ca2+‐induced changes in K+ permeability are lost or inactivated during membrane isolation. An intact cytoarchitecture may be required for RVD.
Cell shape and growth regulation in skeletal muscle: Exogenous versus endogenous factors
Authors: Vandenburgh Herman H. 
Published: February 2005

AbstractPassive stretch (10–12%) of tissue‐cultured avian skeletal myotubes in serum‐containing medium stimulates myotube growth in a manner analogous to hormonal stimulation of adult muscle. The resulting increase in myotube length is accompanied by marked reduction in the number of surface microvilli seen by scanning electron microscopy. We investigated the possible involvement of exogenous growth factors in the transduction of stretch‐induced alterations in cell shape into the concurring biochemical changes that are associated with cell growth. We show that the acute stimulation of myotube amino acid transport and protein synthesis by stretch are independent of serum growth factors in the culture medium by evidence obtained from serum dose‐response experiments. The myotubes synthesize and secrete high molecular weight factors into their culture medium, which regulates myotube amino acid transport and protein synthesis. Stretch of the myotubes did not alter the appearance of these factors in the culture medium. The initial growth‐related biochemical alterations induced by myotube stretch in vitro thus depend only on events intrinsic to the cells. However, subsequent stretch‐induced growth of the myotubes occurs only in serum‐containing medium. There are both serum‐independent and serum‐dependent steps in the transduction of the stretch stimulus into myotube growth.
Reduced free‐methionine in methionine‐dependent SV40‐transformed human fibroblasts synthesizing apparently normal amounts of methionine
Authors: Stern Peter H. , Mecham James O. , Wallace C. Douglas , Hoffman Robert M. 
Published: February 2005

AbstractMany different types of cancer cells have been shown to be methionine‐dependent. These cells, unlike normal cells, grow poorly or not at all when methionine is replaced by its immediate precursor homocysteine in the growth medium (Met−Hcy+ medium). We have previously shown that apparently normal total amounts of methionine are synthesized by methionine‐dependent SV40‐transformed human fibroblasts. However, methionine‐dependent cells in Met−Hcy+ medium accumulate reduced amounts of S‐adenosylmethionine (AdoMet) and elevated amounts of S‐adenosylhomo‐cysteine (AdoHcy) that together probably limit growth. In this report, we demonstrate that the amount of free methionine is low in methionine‐dependent SV40‐transformed human fibroblasts in Met−Hcy+ medium compared to normal human diploid fibroblasts. In contrast, in Met+Hcy− medium, the amount of free methionine is comparable in both cell types. The deficient pool of free methionine in methionine‐dependent cells in Met−Hcy+ medium allows only low amounts of AdoMet to be formed. However, large amounts of the biosynthesized methionine are channeled into protein synthesis. Possible mechanisms are discussed to explain this cancer‐associated metabolic defect.
Anchorage dependence and Ca2+ requirement are independently modulated by hydrocortisone hormone in rat C6 glioma cells
Authors: Armelin Mari C. S. , Armelin Hugo A. 
Published: February 2005

AbstractWe had previously shown that hydrocortisone (Hy), a glucocorticoid hormone, regulates the expression of the transformed phenotype of rat C6 glioma cells. The hormone reversibly renders C6 cells dependent on anchorage and high Ca2+ concentration for growth. We had also isolated Hyresistant C6 variants in agarose suspension cultures. Here we report that Hyresistant variants selected in high (1.8mM) Ca2+ medium become growth‐arrested in low (30 μM) Ca2+ medium upon hormone treatment. We conclude that Hy‐induced anchorage dependence and Hy‐induced high Ca2+ requirement for growth of C6 glioma cells, are two independent phenotypes.
Distribution and mobility of concanavalin a receptors on isolated guinea pig epidermal cells at various stages of differentiation
Authors: Takigawa Masahiro , Danno Kiichiro , Furukawa Fukumi 
Published: February 2005

AbstractTrypsinized guinea pig epidermal cells were separated by velocity sedimentation at unit gravity. Based on the relationship between cell size and both morphological and functional aspects of differentiation, the cells were classified as lower (a diameter <12.5 μM), middle (a diameter between 12.5 and 15 μM), and upper (a diameter >15 μM) epidermal cells. Fresh cells exposed to rhodaminated concanavalin A (Con A) were sedimented and reacted with fluoresceinated anti‐Con A serum to distinguish cell surface Con A from intracellular lectin. Labeling at 4°C resulted in a uniform surface distribution of Con A irrespective of cell size. After a 1‐hr incubation of Con A‐labeled cells in lectin‐free medium at 37°C, lower epidermal cells and approximately half of middle epidermal cells internalized Con A/receptor complexes by endocytosis while lectin remained diffusely on the remainder of middle epidermal cells and upper epidermal cells. By electron microscopy, ferritin‐Con A was clustered on surface areas and invaginations of the plasma membrane before being endocytosed. We concluded that the differentiation of epidermal cells was accompanied by progressive decrease in endocytosis and, most probably, mobility of Con A receptors.
Transferrin receptor expression during exponential and plateau phase growth of human tumour cells in culture
Authors: Musgrove E. , Rugg C. , Taylor I. , Hedley D. 
Published: February 2005

AbstractTransferrin receptor expression by the human tumour cell lines CCRF‐CEM leukaemia and PMC‐22B melanoma was studied, measuring the specific binding of fluorescein isothiocyanate (FITC)‐labelled transferrin using a fluorescence‐activated cell sorter. By measuring the fluorescence of cells stained at subsaturating concentrations of conjugate it was possible to calculate the average numbers of receptors per cell and the binding affinity by Scatchard analysis. These values (1.9 × 105 binding sites/cell, KA 1.2 × 109 M−1 for CCRF‐CEM during exponential growth and 6.9 × 104 binding sites/cell, KA 1.4 × 10−9 M−1 for PMC‐22B) are in close agreement with previously published data obtained using radiolabelled transferrin. The present method, however, allowed the transferrin receptor expression of individual cells within a population to be measured and thus it has been possible to test the hypothesis that transferrin receptor is a marker for cycling cells. Frequency‐distribution histograms of transferrin receptor showed a wide range of values for both cell lines during exponential growth. When the extreme ranges were sorted and the cells examined for cellular DNA content it was found that those with the highest transferrin receptor expression were enriched with cells in S, G2, and M phases of the cell cycle, whereas those with low transferrin receptor expression were mainly in G1. However, two‐parameter‐correlated dot plots of transferrin receptor expression versus DNA content showed there was considerable overlap between the ranges of receptor expression for the different cell cycle compartments. Using a stathmokinetic method we have measured the proportion of quiescent cells in fed plateau phase cultures. Transferrin receptor expression was downgraded under these growth conditions but, contrary to expectation, the decline affected the population uniformly, without the emergence of a distinct, transferrin receptor‐negative subpopulation corresponding to the increasing proportion of quiescent cells. Thus, although transferrin receptor expression bears some relation to cell cycle phase and reflects the proliferative activity of populations of cells, it is incapable of identifying individual cells which are out of cycle.
In vitro characteristics of the lipid‐filled interstitial cell associated with postnatal lung growth: Evidence for fibroblast heterogeneity
Authors: Maksvytis Harvey J. , Niles Richard M. , Simanovsky Leonid , Minassian I. A. , Richardson Laura L. , Hamosh Margit , Hamosh Paul , Brody Jerome S. 
Published: February 2005

AbstractThis study explores the in vitro modulation of the lipid‐filled phenotype of the lipid interstitial cell (LIC) isolated from the developing rat lung. Isolated LIC lose their cytoplasmic lipid droplets when cultured in fetal bovine serum (FBS) but retain their potential for lipid storage, since they rapidly reaccumulate lipid when subcultured in neonatal rat serum (NRS) and to a lesser extent in adult rat serum (ARS). The return of LIC to a lipid‐filled state may not represent cell differentiation, since it occurs in the presence of bromodeoxy‐uridine. NRS contains twice the free fatty acids (FFA) of FBS and ARS, and doubling the FFA concentration of FBS and ARS increases LIC storage lipids. Serum triglyceride (TG) is 10 times higher in ARS and 23 times higher in NRS than in FBS. Since LIC lipoprotein lipase (LPL) activity is in the range of 3T3‐L1 adipocytes (0.56 vs. 1.72 units/mg DNA), the LIC has the potential of incorporating serum lipoprotein‐triglyceride. The LPL activity of LIC is 9–12 times that of fetal and adult rat lung fibroblasts and 50 times that of human lung, trachea, or skin fibroblasts; LIC are probably a source of endothelial LPL in the developing lung. The response of LIC and ARLF cyclic‐AMP to hormones known to influence lipid synthesis or degradation showed that: only LIC responded to glucagon; prostagladin E1 was a more potent stimulus to LIC; isoproterenol was a more potent stimulus to ARLF; and neither cell responded to ACTH. The unique nature of LIC tends to support further the concept of fibroblast heterogeneity within tissues.
Homologous and heterologous mitogenic desensitization of Swiss 3T3 cells to phorbol esters and vasopressin: Role of receptor and postreceptor steps
Authors: Collins Mary K. L. , Rozengurt Enrique 
Published: February 2005

AbstractProlonged treatment of Swiss 3T3 cells with phorbol 12,13 dibutyrate (PDB) rendered the cells refractory to subsequent mitogenic stimulation by both PDB and vasopressin. In contrast, the cells retained full responsiveness to a wide variety of other mitogens. An early response to vasopressin and phorbol esters, inhibition of (125l)‐labeled epidermal growth factor [(125l)‐EGF] binding, was also substantially decreased in PDB pretreated cells. The cross desensitization was not produced by vasopressin; this ligand induced homologous but not heterologous desensitization. Exposure of Swiss 3T3 cells to PDB caused a down regulation of (3H)‐PDB receptors but did not reduce the binding of vasopressin to refractory cells. The time‐course (t1/2 = 7 h) and dependence on PDB concentration (half maximal at 20 nM) for this phorbol ester receptor loss paralleled the induction of the mitogenic desensitizations to both PDB and vasopressin. However, the time‐course of recovery revealed an important dissociation between receptor presence and mitogenic response.When Swiss 3T3 cultures, which had been pretreated with PDB, were washed to remove this ligand and incubated in its absence for 24 h, both (3H)‐PDB receptors and PDB or vasopressin inhibition of (125l)‐EGF binding were almost completely restored to control levels. However the homologous and heterologous mitogenic desensitizations showed a very different reversal time. After a 24‐h recovery period PDB‐treated refractory cells were still unable to synthesize DNA in response to PDB or vasopressin. The mitogenic desensitizations were however completely reversible; after a 48‐h incubation in the absence of PDB the cells responded fully to the mitogenic actions of PDB or vasopressin. This finding suggests that a further postreceptor step was also desensitized by prolonged PDB treatment. The presence of a low level of cycloheximide during the PDB pretreatment blocked induction of this postreceptor refractoriness. We propose that this refractory postreceptor step selectively blocks both PDB and vasopressin stimulation of DNA synthesis and may represent the point at which the mitogenic pathways of phorbol esters and vasopressin converge.
Interaction of T lymphocytes and macrophages with cultured vascular endothelial cells: Attachment, invasion, and subsequent degradation of the subendothelial extracellular matrix
Authors: Savion N. , Vlodavsky I. , Fuks Z. 
Published: February 2005

AbstractCirculating macrophages and T lymphocytes can invade the vascular endothelium and migrate from the circulatory system to an extravascular compartment such as inflammatory organs. In an in vitro model system we have examined the capacity of murine T lymphocytes and peritoneal macrophages to attach and invade a confluent vascular endothelial cell monolayer and to degrade sulfated proteoglycans in the subendothelial extracellular matrix.Concanavalin A and antigen‐specific (egg albumin) activated T lymphocytes labeled with [3H]thymidine attached to the apical surface of the vascular endothelium in a time‐dependent manner. A subsequent invasion of the endothelial cell monolayer was observed by scanning electron microscopy. Both activated T lymphocytes and murine macrophages degraded the [35S]O4=‐containing fragments in a process which required cell‐matrix contact but was not dependent on serum proteases.Sulfated glycosaminoglycan chains produced from matrix proteoglycans by treatment with papain or alkaline borohydride were 3–4 times larger than the cell‐mediated degradation fragments. This suggests that both macrophages and T lymphocytes elaborate upon stimulation an endoglicosidase capable of cleaving glycosaminoglycans specifically and releasing heparan sulfate‐rich fragments. The ability of activated cells of the immune system to attach and invade the vascular endothelium and to degrade sulfated proteoglycans is very similar to that reported for highly metastatic tumor cells.
An examination of the efficiency of glucose and glutamine as energy sources for cultured chick pigment epithelial cells
Authors: Barbehenn E. K. , Masterson E. , Koh Shay‐Whey , Passonneau J. V. , Chader G. J. 
Published: February 2005

AbstractEmbryonic chick pigment epithelial cells in culture require glucose as their major energy source for long‐term growth, pigment formation, and colony organization. Cell number increases with glucose concentration at least up to 5.0 mM. Cells can be grown with glutamine as the major energy source but produce comparable cell numbers for only the first 3 days in culture, after which they cease growing. However, they are able to metabolize glutamine at a two to sixfoid higher rate than cells grown in the presence of glucose as measured by CO2 release and by incorporation into protein. In cells grown in the presence of both glucose and glutamine, basal ATP levels were 31.1 nmoles/mg protein; P‐creatine averaged 15.2 nmoles/mg protein and showed marked variability between experimental groups. During starvation, P‐creatine levels fell while ATP levels remained relatively constant. Glucose was required for the recovery of P‐creatine to prestarvation levels when measured 5 min after refeeding. Because of these marked changes in P‐creatine concentration as a function of nutritional status, the ATP/P‐creatine ratio becomes a useful measure of the energy state of the cell.
Compound 48/80 impairs cytokinesis in murine leukemiccells
Authors: Darzynkiewicz Zbigniew , Carter Sally 
Published: February 2005

AbstractCompound 48/80 (poly‐p‐methoxyphenethylmethylamine), an agent commonly used to trigger degranulation of mast cells, at concentrations of 5–20 μg/ml suppresses the proliferation of L1210 and Friend leukemic cells in vitro, inducing the formation of giant cells, which are polykaryons. Both the proportion of polykaryons in cultures and their size (which reflects the number of nuclei per polykaryon) increase during growth in the presence of 48/80 up to 48 hr; thereafter, the cells lose viability. A predominant number of nuclei in these polykaryons contain a 4C, or higher DNA content. The data indicate that compound 48/80 impairs the cleavage (cytokinesis) and perhaps mitotic processes. Mechanisms by which compound 48/80 induces the described effects are unknown but may be related to the polycationic nature of the polymer and its interaction with the cell membrane. Certain attributes of compound 48/80 suggest that this or similar polymers may have value as research tools for the study of regulatory mechanisms involved in cell division.
Calmodulin antagonists sensitize cells to pseudomonas toxin
Authors: Sundan Anders , Sandvig Kirsten , Olsnes Sjur 
Published: February 2005

AbstractL cells and mouse 3T3 cells, which are very sensitive to Pseudomonas aeruginosa exotoxin A (PEA), were protected with weak bases and low concentrations of monensin. BHK cells and a number of other cell lines which are much less sensitive to PEA were much less protected under these conditions. Trifluoperazine, dansylcadaverine, and several other calmodulin antagonists strongly sensitized BHK cells to the toxin whereas they did not affect the sensitivity of the mouse 3T3 and L cells. The sensitization of the BHK cells was counteracted by treatment with weak bases or low concentrations of monensin. Calmodulin antagonists also sensitized cells to toxin which had become inaccessible to antitoxin, indicating that the effect of the calmodulin antagonists is exerted on a process taking place after the toxin is endocytosed.
Differences between the endocytosis of horseradish peroxidase and its conjugate with wheat germ agglutinin by cultured fibroblasts
Authors: Stieber Anna , Gonatas Jacqueline O. , Gonatas Nicholas K. 
Published: February 2005

AbstractA covalent conjugate of wheat germ agglutinin (WGA) with horseradish peroxidase (HRP) was used for a morphologic study of its adsorptive endocytosis by cultured human fibroblasts. Initial binding at 4°C of the conjugate was observed over the entire plasma membrane, including “coated” and smooth pits. Endocytosis of HRP and the WGA‐HRP conjugate was observed in lysosomes, but only the conjugate was seen in a cisterna of the Golgi apparatus (GERL), and in adjacent coated vesicles.
Arrest states in a set of mutants of rat 3Y1 cells temperature‐sensitive for entering S phase
Authors: Zaitsu Hirokazu , Kimura Genki 
Published: February 2005

AbstractFour temperature‐sensitive (ts) mutants of rat 3Y1 cells (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) are arrested at 39.8°C mainly with a 2N DNA content (temperature‐arrested cells). The states of these cells were compared with findings in case of cells arrested at 33.8°C at saturation density (density‐arrested cells), with regard to the ability to enter S phase after release from arrest or after serum stimulation at 39.8°C. With the 3Y1tsD123, the ts defect is an event which seems essential for the initiation of S phase and occurs after mitosis but not after release from the density arrest. The defect in 3Y1tsF121 related to the efficiency of utilization of serum component(s). In case of 3Y1tsG125, the state of temperature arrest appeared to locate between the state of density arrest and the beginning of S phase. There was no significant difference between the density‐ and the temperature‐arrested cells, in case of 3Y1tsH203.
Collagen synthesis by cloned pulmonary artery endothelial cells
Authors: Macarak Edward J. 
Published: February 2005

AbstractPulmonary artery endothelial cells were isolated from bovine fetal blood vessels and used for biosynthetic studies. At confluence, cultures were incubated in minimal essential medium (MEM) without serum containing [U‐14C]proline. After 24 hours, medium was removed and labeled proteins were precipitated by the addition of ammonium sulfate and fractionated by diethylaminoethyl (DEAE)‐cellulose chromatography. The elution profile showed four major peaks and one minor peak. Fractions within each peak were pooled, subjected to digestion by chymotrypsin and/or collagenase, and analyzed by polyacrylamide gel electrophoresis. Peak I contained a collagen which contained approximately 6% of the 3‐hydroxyproline isomer while total hydroxyproline content was approximately 45%. This material was digested by purified bacterial collagenase and had a mobility slightly slower than that of α1(III) which did not change under conditions that reduce disulfide bonds. Upon digestion with chymotrypsin under conditions where native procollagens are converted to α‐chains, this material was digested. These properties suggest that this material is type VIII or EC (endothelial cell) collagen. Peak 2 contained substantial fibronectin while peak 3 contained primarily type III procollagen. The last major peak contained a mixture of collagenous and noncollagenous material. Upon digestion with chymotrypsin, several peptides were generated which were sensitive to bacterial collagenases. The two major chymotrypsin‐resistant components had mobilities slower than that of α(III) and were not disuifide‐bonded.
Partial characterization of a hepatocyte growth factor from rat platelets
Authors: Russell William E. , McGowan Joan A. , Bucher Nancy L. R. 
Published: February 2005

AbstractRat serum has been shown to stimulate DNA synthesis in primary cultures of adult rat hepatocytes 2–3 times more potently than serum from several other mammalian sources, including humans. Parallel to its stimulation of thymidine incorporation into DNA, rat serum increased the total DNA content of the hepatocyte cultures over time, and also increased the frequency of nuclear labeling and mitosis. Moreover, normal rat serum, derived from whole blood (NRS), stimulated DNA synthesis in hepatocytes twice as effectively as platelet‐poor rat serum, derived from plasma (ppNRS). Addition of a rat platelet lysate (RPL) to ppNRS restored the activity to equal that of NRS. The avid binding of the active principle to CM Sephadex and its sensitivity to trypsin digestion suggest that it is a cationic polypeptide with an apparent molecular weight of about 65,000, as determined by gel filtration. It was inactivated by reduction of disulfide bonds, or by exposure to pH below 5.5, to NaCl concentration below 0.05 M, to 65°C for 30 min, or to 100°C for 10 min. Although it resembles the human platelet‐derived mitogen platelet‐derived growth factor (PDGF) in several of its properties, it differs in others. Hence the hepatocyte growth factor from rat platelets, which accounts for 50% of the DNA synthesis‐stimulatory activity of rat serum, appears to be a distinct entity.