bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanochemical proteins, cell motility and cell‐cell contacts: The localization of mechanochemical proteins inside cultured cells at the edge of an in vitro “wound”
Authors: Gotlieb Avrum I. , Heggeness M. H. , Ash J. F. , Singer S. J. 
Published: February 2005

AbstractWe have examined the distribution of several mechanochemical proteins inside rat A10 cells in monolayer culture, both in sparse cultures and at the edges of in vitro “wounds” in confluent cultures. The proteins examined were actin, myosin, tropomyosin, α‐actinin, filamin, and tubulin. In each experiment, a pair of these proteins (one of which was usually actin) were examined simultaneously by double fluorescence staining methods. Actin was specifically stained by a method based on heavy meromyosin binding, whille the other proteins were specifically stained by indirect immunofluorescence procedures. The most important of the various results described was obtained with cells moving out from the edge of an in vitro wound. Within the flat leading lamella of such a cell, there was an extended region in which myosin was severely depleted or absent compared to the proximal regions of the same cells. By contrast, the other proteins were abundantly present throughout the leading lamella, except for tropomyosin, which was somewhat depleted but not as extensively as myosin. In Nomarski optics, there was no detectable morphological differentiation between the region depleted of myosin and the more proximal portion of the same lamella. While the depletion of myosin from the motile regions of cells does not rule out the involvement of some form of an actomyosin sliding filament mechanism, it suggests that other molecular mechanisms for generating motility be seriously considered.
Role of hydrogen bonding in red cell aggregation
Authors: Jan K. K. 
Published: February 2005

AbstractThe role of hydrogen bonding in red cell aggregation induced by dextran was studied with the use of urea, an inhibitor for hydrogen bonding. In order to avoid hemolysis of red cells by the high concentration of urea, the studies were performed on human red cells hardened in glutaraldehyde. The degree of red cell aggregation at Hct = 45% was estimated by the use of a coaxial cylinder viscometer. The viscometric aggregation index (VAI) was calculated from viscosity values at shear rates of 52 sec−1 (ηH) and 0.05 sec−1 (ηL); VAI = (ηL–ηH)/ηH. Red cells with surface charge intact and with charge removal by neuraminidase treatment were studied. Urea at high concentrations, e.g., 6 M, significantly inhibited red cell aggregation induced by dextran. These findings indicate that hydrogen bonding plays an important role in dextran‐induced red cell aggregation. An understanding of the nature of the forces involved in red cell aggregation serves to establish the physicochemical principles of cell‐to‐cell interactions induced by macromolecules.
The growth response of cells in medium made hyperosmolal with electrolytes or mannitol
Authors: Swanson T. Leonard 
Published: February 2005

AbstractA comparison of the growth rates of established human lymphoid and tumor cell lines was performed in nutrient medium made hyperosmolal with mannitol, NaCl, or mixtures of NaCl and KCl at a constant Na/K ratio. It was found that considerably higher osmolalities were attained with mannitol than electrolytes before a reduction in the growth rate of the culture was observed. This suggests that mannitol and electrolytes affected the growth rate through different mechanisms. Mannitol uptake was studied with two of the cell lines and both cell lines were found to be permeable to mannitol. This eventually would have eliminated the osmolality gradient between the interior of the cell and the medium, and could explain why higher osmolalities were obtained with mannitol before the growth rate was effected. In addition, initial experiments showed that these cell lines may also be able to metabolize mannitol.
Effect of cell density on energy‐dependent calcium uptake by Balb/c 3T3 membranes is independent of protein synthesis and attachment to substratum
Authors: Moore Leon , Pastan Ira 
Published: February 2005

AbstractMembranes isolated from subconfluent cultures of Balb/c 3T3 cells have low energy‐dependent calcium uptake activity. Replating confluent cells at low density results in a prompt fall of energy‐dependent calcium uptake by membrane fractions. The level to which uptake activity falls is a function of the density at which the cells are plated (Moore and Pastan, '77b). To determine if regulation of energy‐dependent uptake of calcium by membrane fractions is dependent upon attachment to a substrate and to further characterize conditions that regulate the process, we examined calcium uptake activity of membranes isolated from cells in suspension. With cells in suspension energy‐dependent calcium uptake activity of isolated membranes falls promptly if cells are diluted to a low density (<105 cells/ml) and is a function of cell density. When cells in suspension at low cell densities are concentrated to high cell densities (>2 X 106 cells/ml), calcium uptake activity of the isolated membrane fraction is increased as a function of cell density. These changes of membrane calcium uptake activity occur promptly and do not require protein synthesis.
Insulin stimulation of glucose entry in cultured human fibroblasts
Authors: Howard Barbara V. , Mott David M. , Fields Rose M. , Bennett Peter H. 
Published: February 2005

AbstractThe effect of insulin on glucose entry has been studied in monolayer cultures of human diploid fibroblastic cells. Influence of insulin on total cell glucose incorporation was evaluated using [14C] glucose. Glucose incorporation was increased up to two‐fold in the presence of insulin. Insulin action occurred within 30 minutes and could be observed with insulin concentrations as low as 10−10 M (10 μU/ml). The action of insulin was enhanced by preincubation in glucose‐free medium. After glucose starvation the cells converted glucose primarily to glycogen and nucleotides, and the stimulation by insulin was observed equally in both fractions.Influence of insulin on the kinetics of hexose transport was studied using 2‐deoxyglucose and 3‐0‐methyl glucose. A large diffusion component was corrected using ρ‐chloromercuribenzoic acid or phloridzin. Km for facilitated diffusion averaged 1.9 mM for 2‐deoxyglucose and 5.3 mM for 3‐0‐methyl glucose, and Vmax ranged from 10–24 nmoles/min/mg cell protein. Insulin resulted in a 150% increase in Vmax with no significant change in Km. The data suggest that human diploid fibroblasts can be a useful system for the study of insulin's glucoregulatory action.
Adenosine transport and metabolism in mouse leukemia cells and in canine thymocytes and peripheral blood leukocytes
Authors: Lum Caliann T. , Marz Richard , Plagemann Peter G. W. , Wohlhueter Robert M. 
Published: February 2005

AbstractThe intracellular accumulation of free [3H] adenosine was measured by rapid kinetic techniques in P388 murine leukemia cells in which adenosine metabolism (phosphorylation and deamination) was completely prevented by depletion of cellular ATP and by treatment with deoxycoformycin. Nonlinear regression of integrated rate equations on the data demonstrate that the time courses of labeled adenosine accumulation at various extracellular adenosine concentrations in zero‐trans and equilibrium exchange protocols are well described by a simple, completely symmetrical, transport model with a carrier:substrate affinity constant of about 150 μM. Adenosine transport was not affected by 1 mM deoxycoformycin indicating that this analog has a low affinity for the nucleoside transport system. The transport capacity of dog thymocytes and peripheral leukocytes was similar to that of P388 cells. Transport was not inhibited by deoxycoformycin and remained constant during the first two hours after mitogenic stimulation with concanavalin A.In untreated, metabolizing P388 cells transport was found to be the major determinant of the rate of intracellular metabolism, regardless of the extracellular adenosine concentration (up to at least 160 μM), but the long‐term accumulation (longer than 30–60 seconds) of radioactivity from extracellular adenosine strictly reflected the rate of formation of nucleotides (mainly ATP). The metabolism of adenosine by whole cells was entirely consistent with the kinetic properties of the transport system and those of the metabolic enzymes. At low exogenous adenosine concentrations (1 μM and below) transport was slow enough to allow direct phosphorylation of most of the entering adenosine. The remainder was deaminated and rapidly converted to nucleotides via inosine, hypoxanthine, and IMP. At concentrations of 100 μM or higher, on the other hand, influx exceeded the maximum velocity of adenosine kinase about 100 times so that most of the entering adenosine was deaminated. But since the maximum velocity of adenosine deaminase exceeded those of nucleoside phosphorylase and hypoxanthine/guanine phosphoribosyltransferase about 5 and 100 times, respectively, hypoxanthine and inosine rapidly exited from the cells and accumulated in the medium. A 98% reduction of adenosine transport (at 100 μM), caused by the transport inhibitor Persantin, inhibited adenosine deamination by whole cells to about the same extent as transport, whereas adenosine phosphorylation was relatively little affected; thus in the presence of Persantin, transport and metabolism resembled that occurring at the low adenosine concentration. These and other results indicate that adenosine deamination is an event distinct from transport, which occurs only subsequent to adenosine's transport into the cell.
Differential effects of cytochalasin B and caffeine on control of DNA synthesis in normal and transformed cells
Authors: O'Neill Frank J. 
Published: February 2005

AbstractEvidence is presented which suggests the existence of at least two growth control points in cultured mammalian cells. These controls are in “parallel” rather than in “series.” It is suggested that in normal and some transformed cells the controls are coupled while in SV40 transformed cells and tumor cells they are uncoupled. One control is revealed by cytochalasin B (CB) treatment since in normal and some kinds of transformed cells, CB treatment results in the accumulation or the arrest of cells in G1. In this case, the control is normal or coupled. In DNA tumor virus transformed cells and many cultured tumor cells (excluding human glioblastomas) CB does not arrest cells although it prevents cytoplasmic division. Such cells continue DNA synthesis and nuclear division and become highly multinucleated. The effects of CB are not concentration dependent. Here the control is defective or uncoupled. Another control is revealed by caffeine treatment. Again, normal and some types of transformed cells are accumulated in G1 following caffeine treatment, while SV40 transformed cells and tumor cells continue DNA synthesis unabated. The effects of caffeine in arresting cells are concentration dependent. Similarly the control point revealed by caffeine is coupled in normal cells and altered or uncoupled in some SV40 transformed and tumor cells. Although CB and caffeine do not inhibit DNA synthesis in tumor and SV40 transformed cells when administered separately, they cause G1 accumulation when administered in combination. This observation can be explained by the possibility that some transformed cells can utilize alternate or parallel mechanisms to progress through G1 when one mechanism is blocked (CB or caffeine). When both are blocked the cells become arrested in G1. The human glioblastomas are unique among the cultured human tumors thus far examined since they are partially arrested by CB. However they are like other human tumors in that caffeine does not significantly affect DNA synthesis.
Ribosome biosynthesis in Tetrahymena thermophila. III. Regulation of ribosomal RNA degradation in growing and growth arrested cells
Authors: Sutton Claudia A. , Hallberg Richard L. 
Published: February 2005

AbstractWe have measured the turnover rate of ribosomal RNA in exponentially growing Tetrahymena thermophila cells, cells entering the plateau phase of growth, and nutrient‐deprived (starved) cells. Ribosomal RNA is stable in cells in early log phase growth but it begins to turnover as the cells begin a deceleratory growth phase prior to entering a plateau state. Likewise, rRNA in cells transferred from early log phase growth to a starvation medium begins to be degraded immediately upon starvation. In both cases the degradation of rRNA exhibits biphasic kinetics. A rapid initial exponential degradation with a half time of nine and one‐half hours lasting for six hours is followed by a slower exponential degradation with a half‐life of 35 hours. When starved cells are transferred to fresh growth medium turnover of rRNA ceases. The evidence presented suggests that the alteration in degradation rate is a regulated process which is most likely independent of the cell cycle.
Regulation of phosphodiesterase and ornithine decarboxylase by cAMP is cell cycle independent
Authors: Kaiser Nurit , Bourne Henry R. , Insel Paul A. , Coffino Philip 
Published: February 2005

AbstractCyclic AMP (cAMP) causes growth arrest in G1 and induction of cAMP phosphodiesterase and decrease of ornithine decarboxylase in S49 mouse lymphoma cells. Dibutyryl cAMP treatment of partially synchronized cells causes similar changes in activities of both enzymes, regardless of position in the cell cycle. This suggests that cAMP regulation of these enzymes is not mediated by growth perturbation.
Potentiation by p‐fluorophenylalanine of the division‐delaying effects of high hydrostatic pressure in synchronized Tetrahymena pyriformis
Authors: Walker Eric , Wheatley Denys N. 
Published: February 2005

AbstractCultures of heat‐synchronized Tetrahymena pyriformis, growing in a proteose peptone medium, were subjected to short pulses of the amino acid analogue, p‐flurophenylalanine, and high hydrostatic pressure. The pulses of these agents were chosen so that, when applied individually, they did not appreciably delay cell division. However, combined treatments, analogue pulse followed by pressure pulse, produced a pronounced synergism. The results are interpreted as further evidence to support the inclusion of analogue division proteins in pressure labile assemblies during the progression of Tetrahymena into division.
Rapid alterations in cellular morphology and plasma membrane structure induced in rat thymocytes by mitogenic stimuli
Authors: Hume David A. , Thornton Mary R. , Weidemann Maurice J. , Speth Volker 
Published: February 2005

AbstractUnder conditions where a maximum stimulation of 3‐O‐methyl‐glucose transport is observed, three thymocyte mitogens (concanavalin A, ionophore A23187 and hydrogen peroxide) cause cell rounding and a decrease in the density of intra‐membrane particles on the plasma membrane. The early effects of mitogens on the thymocyte plasma membrane are similar to those of osmotic shock.
Colchicine resistant friend cells: Application to the study of actinomycin D induced erythroid differentiation
Authors: Crichley Valerie , Mager Dixie , Bernstein Alan 
Published: February 2005

AbstractColchicine resistant (CchR) mutants have been isolated from Friend erythroeleukemic cells by successive single‐step selections. Measurements of the rate of uptake of [3H]‐colchicine into whole cells, and the binding of [3H]‐colchicine to cytoplasmic extracts, suggest that these mutants are colchicine‐resistant due to a reduced membrane permeability to colchicine, rather than an altered intracellular colchicine‐binding target. Consistent with this conclusion is the observation that non‐toxic concentrations of Tween–80, a non‐ionic detergent, potentiated colchicine uptake into mutant cells. In addition, these Friend cell mutants, like CchR mutants of other cell types, are cross‐resistant to a variety of unrelated drugs, including daunomycin, puromycin, emetine, and actinomycin D.A comparison of the dose‐response curves for the induction of Friend cell differentiation by actinomycin D of both wild‐type and two CchR cells suggests that actinomycin D permeation is required for its effects on Friend cell differentiation. Potentiation of actinomycin D uptake by Tween–80 significantly lowered the concentration of drug required to induce hemoglobin synthesis in the CchR cells, but had no significant effect on either actinomycin D induction of CchS cells or DMSO induction of both CchS and CchR cells. In common with other chemical inducers of Friend cell differentiation, the addition of actinomycin D results in an early decrease in 86 RbCl uptake, although this effect on transport occurred 14 hours later than that observed with DMSO.
Synthesis of proteins and RNA of the 60S ribosomal subunit in HeLa cells recovering from valine deprivation
Authors: Raikow Radmila B. , Vaughan Maurice H. 
Published: February 2005

AbstractThe synthesis of ribosomes in HeLa cells was studied during recovery from a 20‐hour deprivation for valine. The rates of incorporation of labeled precursors into ribosomal pre‐RNA, processed rRNA, total cellular proteins, and proteins of the 60S ribosomal subunit returned to normal or nearly normal levels immediately after restoration of valine to the medium. Specific proteins of the 60S ribosomal subunit, whose apparent net synthesis is reduced more than that of the other proteins of the 60S ribosomal subunit during valine deprivation, were no longer undersynthesized after valine was restored. This rapid recovery suggests that the apparent decrease in the net rate of synthesis of these ribosomal proteins during valine deprivation is effected at the translational or post‐translational level. No evidence of significant synchrony in any particular stage of the cell cycle was observed after a 20‐hr valine deprivation. Key words: 60S ribosomal subunit; HeLa, cells; valine deprivation.
Growth‐modulating tripeptide (glycylhistidyllysine): Associaton with copper and iron in plasma, and stimulation of adhesiveness and growth of hepatoma cells in culture by tripeptide‐metal ion complexes
Authors: Pickart Loren , Thaler M. Michael 
Published: February 2005

AbstractThe tripeptide H‐Gly‐His‐Lys‐OH (GHL) is a human plasma constituent which has been previously shown to modulate the growth and viability of a variety of cell types and organisms. Experimental observations presented herein indicate that GHL is complexed with the transition metal ions Cu++ and Fe++ in vivo and may exert its biological effects as a peptide‐metal chelate. At physiological pH in vitro, GHL associates with ionic copper, cobalt, iron, molybdenum, manganese, nickel, and zinc, but has no affinity for calcium, manganese, potassium, and sodium. GHL acts synergistically with copper, iron, cobalt, and zinc to alter patterns of cell growth in monolayer cultures of a tumorigenic hepatoma cell line (HTC4). These transition metals induce cellular flattening and adhesion to support surfaces, and inhibit DNA synthesis and lactic acid production when growth is limited by reduction of serum concentrations in medium. These inhibitory effects are neutralized, and intercellular adhesion and growth are stimulated by GHL in medium at nanomolar concentrations. Cu and Fe are the most active metals when combined with GHL. The results suggest that the inability of HTC4 cultures to replicate without adequate concentrations of serum in medium may reflect deficiency of GHL and transition metals, which appear to form complexes prior to interaction with cells. Chelation of transition metals with GHL and, potentially, with other growth‐modulating peptide factors in plasma or medium, may provide a mechanism for expression and regulation of biological activities influenced by transition metals and polypeptide growth factors. The observed effects of GHL‐metal complexes, including stimulation of cellular adhesiveness to substratum (flattening) and intercellular attachment (monolayer formation), appear to satisfy requirements for growth of hepatoma cells in monolayer culture.
Vital DNA staining and cell sorting by flow microfluorometry
Authors: Lydon M. J. , Keeler K. D. , Thomas D. B. 
Published: February 2005

AbstractA procedure has been investigated for sorting viable cells according to their DNA content. Cells are stained with the U.V. activated fluorochromes 4′6‐diamidino‐2‐pheylindole (DAPI), Hoechst 33258 or Hoechst 33342, and sorted with a Fluorescence Activated Cell Sorter. Hoechst 33342 is a suitable vital stain for a varietyof cell types. Hoechst 33258 and DAPI, however, are quantitative vital stains for CHO cells only. Cloning efficiency is unaffected by the sorting procedure, and these stains are not mutagenic at concentrations suitable for vital staining. Potential applications of this procedure to cell biology are discussed.
The cellular basis of self renewal in culture by human acute myeloblastic leukemia blast cell progenitors
Authors: Chang Lawrence J. A. , Till James E. , McCulloch Ernest A. 
Published: February 2005

AbstractBlast cells from patients with Acute Myeloblastic Leukemia (AML) were separated according to cell size using velocity sedimentation under unit gravity. Fractions obtained in this way were plated in methyl cellulose with a growth stimulator present in media conditioned by leukocytes in the presence of phytohemagglutinin (PHA‐LCM). Colonies of blast cells form under these conditions. Pooled cell suspensions from such colonies were plated in microwells; the plating efficiency of such suspensions is a measure of blast progenitor self‐renewal occurring in the original blast colonies. Self‐renewal assays on each fraction indicated that self renewal among blast progenitors is heterogeneously distributed with subpopulations differing in renewal capacities. The results are consistent with the view that blast cell subpopulations in AML undergo a series of transitions associated with decreasing self renewal capacity, analogous to that observed in normal hemopoiesis, where proliferative capacity decreases with increasing differentiation.
Role of lysosomes in protein turnover: Catch‐up proteolysis after release from NH4Cl inhibition
Authors: Amenta J. S. , Brocher S. C. 
Published: February 2005

AbstractCultured rat embryo fibroblasts, when placed in media with 10% serum containing 20 mM NH4Cl, show an inhibition of protein degradation and, concurrently, an accumulation of numerous, large vacuoles, partially filled with cellular debris. Cells placed in a serum‐free media exhibit an enhanced degradation of cell protein, which is also inhibited by NH4Cl. When these cells are removed from media containing NH4Cl and placed in fresh media, the material accumulated in these vacuoles is rapidly and quantitatively released to the media in both an acid‐soluble and acid‐insoluble form. NH4Cl inhibits rapidly and specifically the lysosomal proteolytic mechanism, and is without effect on the basal turnover mechanism. The lysosomal proteolytic mechanism accounts for approximately 25% of protein turnover, and, at least in low density cultures, can be stimulated to levels which account for more than half of the protein turnover in the cell. The major pathway for the degradation of fast turnover proteins appears to be separate from lysosomal mechanism.