bluuebunny/crossref_metadata_2025_split huggingface dataset:
Specific inhibition of endothelial cell proliferation by isolated endothelial plasma membranes
Authors: Teitel Jerome M. 
Published: February 2005

AbstractCultures of human vascular endothelial cells were used to study the phenomenon of density‐dependent inhibition of cell growth. Endothelial cells were disrupted by nitrogen cavitation, and a plasma membrane‐enriched fraction was prepared by differential centrifugation followed in some cases by sucrose density gradient fractionation. Membrane suspension was added to lowdensity early‐passage endothelial cultures grown in microwells. Hemocytometer cell counts and 6 hr 3H‐thymidine pulses were performed in triplicate wells at varying intervals. Plasma membranes suppressed cell proliferation in a reversible, dose‐dependent fashion. Increasing the ambient concentration of endothelial cell growth factor did not alter the inhibitory effect. The antiproliferative effect was sensitive to heat and trypsin and to incubation with 0.1 M sodium carbonate, pH 11.5. Membrane vesicles selectively derived from the apical cell surface also suppressed proliferation. This phenomenon showed at least some specificity for cell type and species in both human and bovine models. Therefore, cell‐cell contact is capable of regulating endothelial cell proliferation in vitro despite the presence of available growth surfaces and of optimally supportive culture medium.
Strain and site dependence of polyploidization of cultured rat smooth muscle
Authors: Rosen Eliot M. , Goldberg Itzhak D. , Shapiro Howard M. , Levenson Stephen E. , Halpin Patricia A. , Faraggi David 
Published: February 2005

AbstractSmooth muscle cell (SMC) growth may play an important role in the pathogenesis of vascular diseases such as atherosclerosis and hypertension. Recent studies have demonstrated that, under different growth stimuli in vivo, SMC may respond by proliferation of diploid cells, polyploidization to the tetraploid (or even octaploid) state, or both. In this study, we used flow cytometry to evaluate the intrinsic tendencies of aortic SMC and nonarterial cells from rats of different strains, ages, and blood pressures to polyploidize in response to in vitro growth stimulation. Significant strain‐related differences in polyploidization of aortic SMC were found (P < 0.001): highest in WKY (normotensive inbred rat related to SHR), intermediate in SHR (genetically hypertensive rat), and lowest in Sprague‐Dawley and Fischer (normotensive outbred and inbred rats). Animal age had less or no effect on the degree of polyploidization. Nonarterial cells (venous SMC and lung cells) from WKY and SHR remained essentially diploid, suggesting tissue specificity of in vitro polyploidization. Studies of the growth kinetics of uncloned and clonal populations of aortic SMC revealed decreased proliferation as the ploidy increased in WKY, SHR, and Sprague‐Dawley, These findings suggest that genetic strain factors as well as cell type/site of origin significantly influence in vitro polyploidization, whereas animal age and blood pressure do not. The findings also emphasize the need to consider ploidy changes when evaluating in vitro SMC growth kinetics. Further studies will improve understanding of SMC growth regulation and the functional significance of vascular polyploidy.
Selective increase of c‐myc mRNA levels by methylglyoxal‐bis (guanylhydrazone) and novobiocin in serum‐stimulated fibroblasts
Authors: Aller Patricio , Baserga Renato 
Published: February 2005

AbstractWe have studied the effect of methylglyoxal‐bis (guanylhydrazone) (MGBG) and novobiocin on the accumulation of specific mRNAs in serum‐stimulated ts13 cells (a temperature‐sensitive mutant of the BHK cell line). The RNAs studied included: c‐myc, v‐ras, ornithine decarboxylase, β‐actin, histone H3, and those represented by clones p2F1 and p1B6 (Hirschhorn et al., Proc. Natl, Acad. Sci. USA, 81: 6004, 1984) All these RNAs accumulated at higher levels when quiescent cells were serum stimulated for 16 h. Both MGBG (25 μM and 100 μM) and novobiocin (200 μg/ml) effectively prevented the transition from G0 to S phase. We found that 100 μM MGBG induced an overaccumulation of c‐myc RNA while H3 RNA was decreased, and the steady‐state levels of all other RNAs were the same as in cells stimulated without the drug. Novobiocin prevented the serum‐induced increase in the amount of all RNAs, which remained at the same levels as in quiescent cells, with the exception of c‐myc, which again accumulated at a higher level in drug‐treated cells than in serum‐stimulated untreated cells. The possible significance of these results is discussed.
Temperature ranges over which rainbow trout fibroblasts survive and synthesize heat‐shock proteins
Authors: Mosser D. D. , Heikkila J. J. , Bols N. C. 
Published: February 2005

AbstractCultures of the rainbow trout fibroblast cell line RTG‐2 withstood temperatures from 0°C to 28°C. At 0°C and 28°C, no prolifertion occurred, but cells persisted for at least 7 days. If the cultures were placed back at 22°C, proliferation returned to normal in those that had been kept at 0°C but was reduced in cultures that had been kept at 28°C. Above 28°C, cultures survived for only short periods. If RTG‐2 cells that were grown routinely at 22°C were shifted to 26, 28, and 30°C, heat shock proteins (hsps) of 100, 87, 70, 68, 60, 39, 27, and 19 kilodaltons were synthesized. Synthesis was most pronounced at 28°C, and at this temperature hsp synthesis was maximal by 2 hr and had returned to control levels by 36 hr. Individual hsps were synthesized maximally at slightly different times and temperatures, but under all conditions hsps 87 and 70 were most abundant. If cultures were shifted to 24°C or 32°C, hsp synthesis was not observed. Neither the placement of cultures at 5°C nor the shift of cultures that had been maintained at 0°C or 5°C back to 22°C induced the synthesis of hsps. However, cultures incubated at 5°C for 24 hr did synthesize hsps at 26°C, 28°C, and 30°C.
Intracellular location of the Ah receptor
Authors: Gudas Jean M. , Karenlampi Sirpa O. , Hankinson Oliver 
Published: February 2005

AbstractThe subcellular distribution of the Ah receptor from the mouse hepatoma line, Hepa‐1, was investigated following cytochalasin B treatment and cell enucleation. Probing the resultant cytoplast and nucleoplast fractions with radiolabelled tetrachlorodibenzo‐p‐dioxin (TCDD) revealed the presence of a specifically bound peak of receptor only in the cytoplast fraction. However, the quantity of receptor recovered in these experiments was only 10–12% of the expected value. We therefore undertook an investigation to determine the fate of the Ah receptor in the presence of cytochalasin B. Incubation of Hepa‐1 cells with this compound resulted in a rapid loss or inactivation of cytosolic binding activity with a concomitant decrease in the amount of receptor partitioned into the nucleus at all time periods examined. Control experiments indicated that cytochalasin B did not compete with TCDD for binding to the Ah receptor and furthermore, that its mechanism of action could not be attributed to a non‐specific effect on all cytosolic proteins. The results obtained are discussed in relation to the proposed models for induction by the estrogen and glucocorticoid binding receptors.
Persistent infection with a nontransforming RNA virus leads to impaired growth factor receptors and response
Authors: Verdin Eric M. , Maratos‐Flier Eleftheria , Carpentier Jean‐Louis , Kahn C. Ronald 
Published: February 2005

AbstractThe potential role of viral persistence with nontransforming viruses on cellular growth and cellular function has received little attention. We found that when infected with type 3 reovirus (five plaque‐forming units (PFU)/cell), balb/C 3T3 cells (a mouse embryo fibroblast cell line) undergo a limited lytic phase. The surviving cells, about 90% of the original cells, appear morphologically normal by light microscopy and exhibit normal growth patterns in serum‐supplemented medium but are persistently infected by electron microscopy. These persistently infected cells shed infectious virus in the culture medium (1.6–60 × 106 PFU per 106 cells per 24 h). In comparison to control uninfected 3T3 cells, the persistently infected cells exhibit a 70–90% decrease in receptor number for epidermal growth factor (EGF). This occurs without production of any EGF‐like material and is associated with a parallel decrease in EGF‐stimulated DNA synthesis. By contrast, insulin receptors are increased in number three‐fold and insulin and serum stimulated DNA synthesis are comparable to control uninfected cells. These results suggest that persistent infection with a nontransforming virus may lead to major alteration in control of cell growth by specific growth factors.
Sodium 22+ washout from cultured rat cells
Authors: Kino Minoru , Nakamura Akitoshi , Hopp Laszlo , Kuriyama Satoru , Aviv Abraham 
Published: February 2005

AbstractThe washout of Na+ isotopes from tissues and cells is quite complex and not well defined. To further gain insight into this process, we have studied 22Na+ washout from cultured Wistar rat skin fibroblasts and vascular smooth muscle cells (VSMCs). In these preparations, 22Na+ washout is described by a general three‐exponential function. The exponential factor of the fastest component (k1) and the initial exchange rate constant (kie) of cultured fibroblasts decrease in magnitude in response to incubation in K+ ‐deficient medium or in the presence of ouabain and increase in magnitude when the cells are incubated in a Ca++ ‐deficient medium. As the magnitude of the kie declines (in the presence of ouabain) to the level of the exponential factor of the middle component (k2), 22Na+ washout is adequately described by a twoexponential function. When the kie is further diminished (in the presence of both ouabain and phloretin) to the range of the exponential factor of the slowest component (k3), the washout of 22Na+ is apparently monoexponential. Calculations of the cellular Na+ concentrations, based on the 22Na+ activity in the cells at the initiation of the washout experiments, and the medium specific activity agree with atomic absorption spectrometry measurements of the cellular concentration of this ion. Thus, all three components of 22Na+ washout from cultured rat cells are of cellular origin. Using the exponential parameters, compartmental analyses of two models (in parallel and in series) with three cellular Na+ pools were performed. The results indicate that, independent of the model chosen, the relative size of the largest Na+ pool is 92–93% in fibroblasts and approximately 96% in VSMCs. This pool is most likely to represent the cytosol.
Heparin inhibition of smooth muscle cell proliferation: A cellular site of action
Authors: Reilly Christopher F. , Fritze Linda M. S. , Rosenberg Robert D. 
Published: February 2005

AbstractThe potential of a given amount of heparin to inhibit smooth muscle cell (SMC) proliferation can be increased more than 13 fold if quiescent cultures are pretreated with this mucopolysaccharide for 48 h. The large increase in antiproliferative activity was attributable to a 74% inhibition of the first cell cycle traverse of SMC after serum addition. If the mucopolysaccharide was added to SMC coincident with serum, the initial cell cycle traverse was only suppressed by 27%. In both heparin pretreated and nonpretreated SMC cultures, 48 to 72 h elapsed before substantial inhibition was observed. The inhibitory effects of heparin were reversible and inversely proportional to the starting cell density of the cultures. The effects of known heparin binding proteins on the inhibitory capability of heparin were examined. Neither platelet‐derived growth factor (PDGF), low density lipoprotein (LDL), nor platelet factor 4 (PF4) were able to reduce the antiproliferative effects. Heparin retained full biological activity in medium containing serum depleted of all heparin binding proteins by heparin‐Sepharose chromatography. These results indicate that heparin does not inhibit growth by preventing serum mitogens or nutrients from interacting with SMC. Rather, our data suggest that heparin is slowly internalized by SMC following binding to specific, non‐PF4 dissociable sites. Heparin may accumulate intracellularly and block a crucial point in the proliferative machinery of SMC.
Activated N‐ras gene induces neuronal differentiation of PC12 rat pheochromocytoma cells
Authors: Guerrero Isabel , Wong Henry , Pellicer Angel , Burstein David E. 
Published: February 2005

AbstractActivated mouse N‐ras gene transfected into PC12 rat pheochromocytoma cells suppressed proliferation and promoted neuronal differentiation. Normal mouse N‐ras in a LTR‐containing vector caused differentiation with a reduced efficiency, but normal N‐ras in a vector lacking LTR sequences failed to alter the PC12 phenotype. Cultures of NGF‐resistant PC12 variant subline U7 also showed outgrowth of neurites and cessation of cell division following transfection with the mutated ras gene. The present findings suggest that ras genes can, in certain cells, play a role in promoting differentiation and suppressing proliferation, in contrast to their established oncogenic neoplasiapromoting activity in other cells.
Dexamethasone and dimethylsulfoxide as distinct regulators of growth and differentiation of cultured suckling rat hepatocytes
Authors: Baribault Hélène , Marceau Normand 
Published: February 2005

AbstractDexamethasone can promote the differentiation of different tissues in vivo while dimethylsulfoxide is a commonly used inducer of differentiation in various tumor cell types in culture. In the present study, the effects of dexamethasone and dimethylsulfoxide on growth and functional activities of cultured differentiating suckling rat hepatocytes stimulated with various combinations of EGF, insulin, and glucagon were evaluated. Hepatocytes stimulated with ECF and either insulin or glucagon entered S phase and mitosis after a lag period of 24 h. These hormonal factors thus provide simple combinations of hepatocyte‐growth regulators. Dexamethasone in the presence of EGF and glucagon inhibited the initiation of DNA synthesis and mitosis, but it had no effect on EGF‐insulin stimulated cultures. Such a differential effect of dexamethasone was observed at concentrations ranging from 4 nM to 200 μM. α‐Fetoprotein, albumin, and tyrosine aminotransferase were used as typical markers of hepatocyte differentiation status. Irrespective of the combinations of growth‐promoting factors used, dexamethasone inhibited α1‐fetoprotein production and maintained albumin production and tyrosine aminotransferase inducibility. In contrast, dimethylsulfoxide at 2% inhibited hepatocyte growth and supported the maintenance of the production of both α1‐fetoprotein and albumin, independent of the hormonal growth regulators used. On this basis, dexamethasone and dimethylsulfoxide act as distinct modulators of growth and maturation of cultured differentiating suckling rat hepatocytes.
Changes of serum‐induced ornithine decarboxylase activity and putrescine content during aging of IMR‐90 human diploid fibroblasts
Authors: Chenc Kuang Yu , Chang Zee‐Fen , Liu Alice Y.‐C. 
Published: February 2005

AbstractThe roles of ornithine decarboxylase (ODC, EC 4.1.1.17) and polyamines in cellular aging were investigated by examining serum‐induced changes of these parameters in quiescent IMR‐90 human diploid fibroblasts as a function of their population doubling level (PDL) and in human progeria fibroblasts. Serum stimulation caused increases of ODC and DNA synthesis in IMR‐90 human diploid fibroblasts, with maximal values occurring, respectively, 10 hr and 22 hr after serum stimulation. Both serum‐induced ODC activity and DNA synthesis in IMR‐90 cells were found to be inversely related to their PDL. Maximal ODC activity and DNa synthesis in young cells (PDL = ∼ 18–22) were, respectively, five‐fold and six‐fold greater than that in old cells (PDL = ∼ 50–55), which in turn were comparable or slightly higher than that in progeria fibroblasts. Polyamine contents (putrescine, spermidine, and spermine) in quiescent IMR‐90 cells did not show significant PDL‐dependency. The putrescine and spermine contents in quiescent progeria cells were comparable to those in quiescent IMR‐90 cells. The spermidine content in quiescent progeria cells, however, was extremely low, less than half of that in quiescent IMR‐90 cells. Serum stimulation caused a marked increase in putrescine content in young cells but not in old cells or in progeria cells. The spermidine and the spermine content in IMR‐90 cells, either young or old, and in progeria cells did not change significantly after serum stimulation. Our study indicated that aging of IMR‐90 human diploid fibroblasts was accompanied by specific changes of polyamine metabolism, namely, the serum‐induced ODC activity and putrescine accumulation. These changes were also observed in progeria fibroblasts derived from patients with Hutchinson‐Cilford syndrome.
Stimulation of bovine endothelial cell angiotensin‐I‐converting enzyme activity by cyclic AMP‐related agents
Authors: Krulewitz A. H. , Fanburg B. L. 
Published: February 2005

AbstractBovine pulmonary artery endothelial cells in culture were used to assess the influence of cyclic nucleotides, isoproterenol (β adrenergic agonist), and theophylline (phosphodiesterase inhibitor) on angiotensin‐I‐converting enzyme (ACE) activity of the cells and culture medium. Dibutyryl cAMP (10−3 M) but not cAMP or dibutyryl cGMP stimulated angiotensin‐l‐converting enzyme (ACE) activity of cells in culture approximately 50–100% but had little influence on ACE activity of the medium. Theophylline at 10−3 M concentration produced a three‐ to fourfold stimulation of both cellular and medium ACE activity. Isoproterenol by itself had no effect on cellular ACE activity but produced a stimulatory effect at 10−7‐10−5 M concentration after pretreatment of cells for 24 hr with 10−4 M theophylline. The results support the concept that ACE activity of endothelial cells is influenced by the cyclic AMP system. ACE activity in cells and that released into medium may be under different regulatory controls.
Effect of inositol hexaphosphate on the transient behavior of red cells following a DMSO‐induced osmotic pulse
Authors: Franco Robert S. , Barker Robin , Novick Steven , Weiner Murray , Martelo Orlando J. 
Published: February 2005

AbstractAn osmotic pulse can be used to incorporate inositol hexaphosphate (IHP) into red cells. The pulse is induced by equilibrating a red cell suspension with DMSO and then rapidly diluting with an isotonic IHP solution. Since IHP binds to hemoglobin and lowers the affinity for oxygen, this method may find application in the preparation of low‐affinity cells for experimental and clinical use. The experiments reported here examined the dynamic changes of several red cell variables immediately following the osmotic pulse. The effect of IHP, which has been shown to dissociate red cell cytoskeletons, was evaluated by comparison with a matched phosphate‐buffered saline (PBS) diluent. Red cell morphology, volume, and hemoglobin permeability were studied by fixing the cells at times ranging from 0.06 to 300 sec after dilution. Mechanical fragility was measured by subjecting the cells to a short period of shear stress at the same times after dilution. With both diluents, the cells underwent a rapid increase in volume followed by a return towards normal volume with a maximum at less than 250 msec. With IHP diluent, the period of hemoglobin permeability immediately followed the size peak and was completed by about 1 sec after dilution. PBS also induced a second leakage at longer times (10–120 sec), which resulted in a morphological dichotomy with ghosts and intact cells. The choice of diluent also affected sensitivity to shear stress. The IHP‐treated cells had a mechanical fragility maximum at about 1 sec. The PBS‐treated cells exhibited no enhanced mechanical fragility. An unexpected result was the inhibition of the second phase of lysis in PBS‐treated cells by a properly timed shear stress.
Osteoclasts and osteoblasts migrate in opposite directions in response to a constant electrical field
Authors: Ferrier Jack , Ross Stephen M. , Kanehisa Junya , Aubin Jane E. 
Published: February 2005

AbstractWe have investigated in vitro the effects of the electrical field produced by constant current on freshly isolated rabbit osteoclasts and on well characterized clonal rat osteoblastlike cells. At field strengths of 0.1 and 1 V/mm, the osteoclasts migrated rapidly toward the positive electrode, whereas the osteoblastlike cells migrated in the opposite direction, toward the negative electrode. Thus, different cell types from the same tissue can respond differently to the same electrical signal. These results have important implications for hypotheses concerning the cellular mechanism of galvanotaxis, and may also clarify the cellular basis of the clinical application of electrical stimulation of bone healing.
Inhibition by phorbol esters of antiimmunoglobulin induced calcium signalling and B‐cell activation
Authors: Rothstein Thomas L. , Kolber Donna L. , Simons Elizabeth R. , Baeker Thomas R. 
Published: February 2005

AbstractThe inhibitory effect of phorbol dibutyrate (PDB) on B‐cell stimulation was evaluated using a model in which activation is induced by modest doses of antiimmunoglobulin antibody (anti‐lg) and progression to DNA synthesis is induced by cytochalasin. PDB preferentially inhibited anti‐lg‐induced activation and did so during brief (2 hr) preincubation with anti‐lg. Activation was inhibited whether PDB was added before or shortly after anti‐lg. Since activation for cytochalasin responsiveness appears to be mediated by Ca2+, the effect of PDB on the anti‐lg‐induced rise in intracellular Ca2+ was evaluated. PDB (and other phorbol esters that activate protein kinase C) inhibited the rise in Ca2+ normally associated with anti‐lg treatment; moreover, PDB reversed an established anti‐lg‐induced Ca2+ response. These data suggest that phorbol esters inhibit B‐cell activation by interfering with the elevated levels of intracellular Ca2+ produced by cross‐linking of surface immunoglobulin by anti‐lg. This could represent a “feedback inhibition” type of response, but it remains to be seen if this occurs under physiological conditions of protein kinase C activation.