bluuebunny/crossref_metadata_2025_split huggingface dataset:
Current status of the thiol redox model for the regulation of hexose transport by insulin
Authors: Czech Michael P. 
Published: February 2005

AbstractData obtained over the last two years pertinent to the thiol redox model for the modulation of hexose transport activity by insulin is summarized. The model proposes that activation of hexose transport in fat cells involves sulfhydryl oxidation to the disulfide form in a key protein component of the fat cell surface membrane. Theoretically, the rapid activation of transport by insulin may involve either the conversion of inactive membrane carriers to the active form as originally proposed, or the conversion of a low Vmax transport system to a high Vmax form. The present experiments showed that the percent inhibition of insulin‐activated transport rates by submaximal levels of cytochalasin B was decreased compared to its effects on basal transport. Treatment of fat cells with N‐ethylmaleimide inhibited cytochalasin B action but not transport activity. When insulin or the oxidant vitamin K5 was added to cells 5 minutes before the N‐ethylmaleimide, the elevated transport activity was also resistant to the sulfhydryl reagent, but cytochalasin B retained its potent inhibitory effect on transport. The data demonstrate that unique properties characterize basal versus insulin‐activated transport activity with respect to the sensitivity of cytochalasin B action to sulfhydryl blockade in isolated fat cells. The data are consistent with the concept that activation of transport activity reflects the conversion of a reduced (sulfhydryl) system characterized by a low Vmax to an oxidized (disulfide), high Vmax transport system.
Regulation of glucose transport in chick fibroblasts: Bicarbonate, lactate and ascorbic acid
Authors: Amos H. , Christopher C. W. , Musliner T. A. 
Published: February 2005

AbstractThe rate at which chick embryo fibroblasts in primary or secondary culture transport glucose or 3‐O‐methyl glucose is strongly influenced by the presence of bicarbonate ion in the culture medium. Cells growing or maintained on glucose at physiologic concentration (5.5mM) have an 8 to 10‐fold higher rate of glucose uptake than their counterparts cultivated without bicarbonate. These cells also produce more lactate as a consequence of their more rapid intake of glucose. The hydrogen acceptors, methylene blue and dehydroascorbate added to the culture medium reduce the cell capacity to transport glucose and 3‐O‐methyl glucose to levels obtaining in the bicarbonate‐free medium. There is a concomitant reduction in glucose utilized by cells during 24 hours and a further reduction in lactate formed per molecule of glucose metabolized.
Sodium: A regulator of glucose uptake in virus‐transformed and nontransformed cells
Authors: Bader John P. 
Published: February 2005

AbstractObservations of cells transformed by the Bryan strain of Rous sarcoma virus (RSV‐BH) suggested that the intracellular concentrations of sodium ion (Na+) may play a critical role in cellular metabolism. In an attempt to manipulate intracellular Na+, chick embryo cells were exposed to graded concentrations of Na+ in the cellular growth medium, and the effect on capacity for glucose uptake was examined. After incubation for six hours, the incorporation rate of 2‐deoxyglucose (used as a substitute for glucose) was proportional to the external Na+ concentration over the range, 100 mM to 200 mM. Cells transformed by RSV‐BH were less responsive than nontransformed cells to differences in Na+ at low concentrations. The changes were specifically dependent upon Na+, since K+, Li+, or choline+ were ineffective as substitutes, and increasing the ionic strength above that of 120 mM Na+ was effective only when Na+ was the added cation.
Transport as a rate limiting step in glucose metabolism in virus‐transformed cells: Studies with cytochalasin B
Authors: Bissell Mina J. 
Published: February 2005

AbstractSteady‐state kinetic tracer analysis and two‐dimensional chromatography and autoradiography were used to examine the relation of glucose transport to its metabolism in cultured chick embryo fibroblasts. Cytochalasin B was added to Rous sarcoma virus‐infected cells to bring the rate of glucose uptake to the level of uninfected cells. It is concluded for chick cells in culture that: (1) the transport of glucose, rather than its phosphorylation, is the rate limiting step and (2) the difference in aerobic glycolysis between normal and virus‐transformed cells at physiological glucose concentration may be a consequence of the difference in the rates of glucose uptake.
Some physicochemical properties of plasma membrane vesicles
Authors: Wallach Donald F. H. 
Published: February 2005

AbstractThe plasma membranes of many animal cells can be disrupted into small sealed vesicles that can be purified centrifugally and utilized for studies on membrane transport. The vesicles behave as micro‐osmometers. However, the presence of charges fixed at the internal and external surfaces of the membrane walls produce pH levels at these surfaces that deviate considerably from bulk pH. Transverse symmetry of charge distribution further leads to transverse asymmetry of surface pH. Finally, charges fixed at the internal membrane surface produce significant Donnan osmotic effects that depend upon membrane composition and ionic environment.
Cooperative binding of concanavalin a to thymocyte membrane vesicles augments uptake of α‐aminoisobutyrate
Authors: Schmidt‐Ullrich Rupert , Mann Nathan D. , Wallach Donald F. H. 
Published: February 2005

Abstract(1) Membrane vesicles from rabbit thymocytes accumulate α‐aminoisobutyrate in the presence of 0.1 M NaCl. Uptake is 1/2 maximal after about 2 min and reaches a plateau value (61 pmoles/mg protein) after 30 min. (2) Up to 25 μg concanavalin A/ml, binding of the lectin describes a sigmoid curve indicative of a cooperative process. (3) At lectin concentrations up to 8 μg/ml, lectin binding enhances the uptake of α‐aminoisobutyrate (maximally 30%).
Uptake of α‐aminoisobutyric acid and phosphate by membrane vesicles derived from growing and quiescent fibroblasts
Authors: Nilsen‐Hamilton Marit , Hamilton Richard T. 
Published: February 2005

AbstractMembrane vesicles derived principally from the plasma membrane and endoplasmic reticulum of mouse 3T3 cells transformed by Simian virus 40 take up α‐aminoisobutyric acid (AIB) and phosphate (Pi). When NaCl is added simultaneously with AIB or Pi, uptake rises two‐ to three‐times above the equilibrium uptake value found in the absence of NaCl.The ability to accumulate AIB or Pi over the control value, in the presence of a Na+ gradient, is almost lost in membrane vesicles derived from benzpyrene‐transformed 3T3 cells (BP3T3) arrested in the G1 phase of the cell cycle by serum starvation.When added to the membranes with NaCl and the uptake substrate, a combination of fibroblast growth factor (FGF) and epidermal growth factor (EGF) restores the ability of the membranes to accumulate AIB and Pi over the control value.
Large scale purification and further characterization of a rat liver cell conditioned medium multiplication stimulating activity
Authors: Dulak Norman C. , Shing Yuen W. 
Published: February 2005

AbstractThe application of roller‐bottle cell culture techniques and a relatively simple purification scheme has led to the isolation of milligram quantities of a polypeptide cell multiplication stimulating activity (MSA) from Buffalo rat liver cell conditioned medium. We have characterized the apparently homogeneous MSA with respect to its biological activity, its N‐terminal amino acid residue, and its amino acid composition, and have tested the MSA for growth‐promoting activity in a number of cell types.
Delayed malignancy and altered growth properties of somatic cell hybrids between rat hepatoma and mouse L‐cells
Authors: Lyons Linda B. , Thompson E. Brad 
Published: February 2005

AbstractSomatic cell hybrids of mouse L‐cells with rat HTC cells were studied for their growth properties in vitro and tumorigenicity in vivo. Three hybrid clones were selected for detailed study. All were delayed in tumor formation in nude mice compared with the parent lines despite their varied growth properties in vitro.One clone was sensitive to density dependent inhibition of growth (DDIG) and had a relatively low saturation density. A second clone was not sensitive to DDIG and had a higher saturation density. The third clone had atypical morphology, was insensitive to DDIG, and had a relatively high saturation density. All of the clones studied produced colonies suspended in agarose gel which were much smaller than those of the parents incubated for the same period of time. Only the pattern of growth in agarose gel corresponded to the delayed tumor formation in vivo of the hybrids. Sensitivity to DDIG and saturation density were not consistent with tumor growth.The hybrid clone that was sensitive to DDIG was the only one of the three that had a nearly complete set of chromosomes derived from each of the parents. The chromosome numbers of all three clones were unchanged after growth in agarose or as tumors in the nude mice.
Surface exposure of glycosaminoglycans in resting, growing and virus transformed 3T3 cells
Authors: Vannucchi Simonetta , Chiarugi Vincenzo P. 
Published: February 2005

AbstractGlycosaminoglycans (GAGs) were released by trypsin from the surface of cultured mouse cells (3T3) in two different growing states: during log‐growth phase and during resting due to serum starvation. Doubly labelled molecules from resting cells were compared with those from growing as well as from transformed cells. Reproducible differences in the elution pattern during ion exchange chromatography and in susceptibility to specific hydrolytic enzymes have been demonstrated: the GAGs pattern of growing normal cells is similar to the pattern of the cells transformed by either Polyoma or SV‐40 viruses and very different from the pattern of resting cells. Growing and transformed 3T3 show a relatively low amount of trypsin removable heparan sulphate (HS) and a relatively high amount of hyaluronic acid (HA) while resting cells exhibit an opposite ratio between the two GAGs. The lowering of HS and the increase of HA in the cell coat is therefore suspected to be more dependent upon growth than upon transformation.
Premature chromosome condensation and cell cycle analysis
Authors: Rao Potu N. , Wilson Barbara , Puck Theodore T. 
Published: February 2005

AbstractThe application of the phenomenon of premature chromosome condensation for cell cycle analysis in HeLa and CHO cells has been examined. Random populations of HeLa and CHO cells pulse labelled with H3‐TdR were separately fused with mitotic HeLa cells using U.V. inactivated Sendai virus. The resulting prematurely condensed chromosomes (PCC) were scored and classified into G1, S and G2‐PCC on the basis of both morphological and autoradiographic data. The results of this study indicated that the G1, S and G2 phase cells are equally susceptible to virus‐induced fusion with mitotic cells and subsequent induction into PCC. Hence the PCC method for cell cycle analysis is both practical and accurate. This study also revealed that the process of chromosome decondensation initiated during the telophase of mitosis continues throughout the G1 period reaching an ultimate state of decondensation by the end of G1, at which point the fusion of such cells with those in mitosis yield PCC with the most diffused morphology instead of the discrete single stranded structures characteristic of early G1‐PCC. Thus, the decondensation of chromatin during G1 appears to be a prerequisite for the subsequent initiation of DNA synthesis.
The effect of elevated potassium on the time course of neuron survival in cultures of dissociated dorsal root ganglia
Authors: Scott Brian S. 
Published: February 2005

AbstractThe effect of potassium (K+) on the time course of neuron survival has been investigated by counting neurons over a 24‐day period in live cultures of dissociated dorsal root ganglia from embryonic chick, fetal and newborn mouse, and fetal human material. In both normal K (6 mM) and in elevated K (20 mM mouse and human, 40 mM chick) there was initially a rapid exponential decrease in neuron survival. However, the magnitude of this decrease was less in the elevated K. In normal K neuron number decreased monotonically; the rate of degeneration itself decreased with time so that after 24 days neuron survival became relatively constant. In contrast, in elevated K the neuron number actually increased over a limited time interval before attaining a stable long‐term value much greater than that in normal K. Thus, elevated K enhanced long‐term survival by causing a lower rate of degeneration and also by causing an increase in neuron number during a limited period of the time in culture. From these observations and other evidence, it is argued that K can substitute to some extent for the trophic action normally exerted by the peripheral field of innervation of the DRG. It is further argued that K acts through its depolarizing effect on the membrane potential and that modification of intracellular ionic concentrations seems less likely to be involved.
Coordinate control of collagen synthesis and cell growth in chick embryo fibroblasts and the effect of viral transformation on collagen synthesis
Authors: Kamine James , Rubin Harry 
Published: February 2005

AbstractUsing collagenase digestion as an assay for collagen in partially synchronized secondary cultures of chick embryo fibroblasts, we find that the rate of collagen synthesis remains at a constant fraction of overall protein synthesis (5%) regardless of the growth rate of the cells even when the rate of protein synthesis is accelerated 5‐fold by adding serum and altering the pH of the culture medium. However, in cells oncogenically transformed by Rous sarcoma virus, the relative rate of collagen synthesis was decreased by 50% 24 hours after infection and was 10% of the initial rate after 5 days. This selective decrease in rate of collagen synthesis could be reversed in cells infected with an RSV temperature‐sensitive transformation‐defective mutant at the non‐permissive temperature, indicating that the decrease in the rate of collagen synthesis was not merely the result of viral infection but was a direct consequence of oncogenic transformation.
Correlated effects of external magnesium on cation content and DNA synthesis in cultured chicken embryo fibroblasts
Authors: Sanui Hisashi , Rubin Harry 
Published: February 2005

AbstractDepletion of Mg2+ in the growth medium for chicken embryo fibroblasts produces a large decrease in DNA synthesis as measured by 3H‐thymidine incorporation, and concomitant decreases in cellular K+ and Mg2+ and increases in Na+ and Ca2+. In cells grown in media containing 0.2 mM Ca2+, graded reduction of Mg2+ from 0.8 mM (control) to 0.016 mM produced graded decreases in DNA synthesis to 10% of control at 0.016 mM Mg2+. Concomitantly, cell cations showed graded changes, Na+ increasing to 227%, K+ decreasing to 52.5%, Mg2+ decreasing to 57.5% and Ca2+ increasing to 153.5% of control. The effects of Mg2+ depletion on DNA synthesis and cell cation content exhibited a dependence on Ca2+ concentration, the effects being larger at low Ca2+ concentration. Use of inorganic pyrophosphate in the growth medium as a selective complexor of Mg2+ caused a marked decrease in DNA synthesis which was accompanied by changes in cellular cation content similar to those produced by direct Mg2+ depletion.The effects of Mg2+ depletion on cell cation content are explainable in terms of changes in membrane permeability caused by rapid external surface exchange of bound divalent cations. Among the several interpretations of the data in terms of possible mechanisms by which changes in external Mg2+ concentration may affect cell metabolism, the most consistent with known properties of the system is the concept of a central role for intracellular free Mg2+ in the coordinate control of growth and metabolism in animal cells.
Effects of sugars on melanogenesis in cultured melanoma cells
Authors: Nakayasu Michie , Saeki Hisaaki , Tohda Hiroko , Oikawa Atsushi 
Published: February 2005

AbstractA permanent cell line C2M of mouse melanoma B16 was highly melanized in a modified Eagle's MEM supplemented with 10% calf serum, when the medium contained 1 mM galactose and 10 mM pyruvate instead of 5.5 mM glucose. The activity of the key enzyme for melanogenesis, tyrosinase (EC 1.14.18.1), of living cells cultured in the galactose‐pyruvate medium was consistently 27 times higher than that of cells in normal MEM. This high level of tyrosinase activity was maintained in the stationary phase, in contrast to the activity of cells in normal medium, which decreased sharply in the stationary phase. It seems likely that tyrosinase activity is suppressed by the presence of glucose rather than stimulated by galactose.This modified medium should be useful for obtaining a high level of tyrosinase activity in living cells in culture and in cell‐free extracts.
Incorporation of purine nucleosides in cultured fibroblasts from a patient with purine nucleoside phosphorylase deficiency and associated T‐cell immunodeficiency
Authors: Burke Wylie G. , Chen Shi‐Han , Scott C. Ronald , Ammann Arthur J. 
Published: February 2005

AbstractCultured skin fibroblasts from a patient with T‐cell immune deficiency and an absence of purine nucleoside phosphorylase activity in red cells were assayed for their capacity to metabolize inosine and guanosine. The cultured fibroblasts were lacking activity of nucleoside phosphorylase and, compared to normal fibroblasts, could incorporate only 2% and 4% of 14C‐inosine and 3H‐guanosine, respectively, into acid precipitable material. Autoradiography visually confirmed the failure of the NP deficient cell line to incorporate the nucleosides into nuclear material. The physiological mechanism by which the deficiency of purine nucleoside phosphorylase causes T‐cell dysfunction remains unclear.
Renal enzymes in kidney cells selected by D‐valine medium
Authors: Gilbert Scott F. , Migeon Barbara R. 
Published: February 2005

AbstractThe ability of D‐valine medium to inhibit fibroblasts in cultures derived from kidneys of various mammals has enabled the selective proliferation of epithelial cells in the absence of fibroblast overgrowth. Studies of these selected epithelial cells have demonstrated the presence of D‐amino acid oxidase, carbonic anhydrase, high levels of alkaline phosphatase and the renal specific pattern of lactate dehydrogenase. The presence of these renal enzymes suggests that the selected epithelial cells are of renal tubular origin and indicates that these differentiated functions are retained in cultured cells.
Nucleoside transport in mammalian cell membranes: A specific inhibitory mechanism of high affinity probes
Authors: Eilam Yael , Cabantchik Z. Ioav 
Published: February 2005

AbstractThe nucleoside transport of systems of hamster cells are susceptible to inhibition by S‐6‐substituted derivatives of mercaptonucleosides. The mechanism of interaction between the most potent inhibitor of the class, 6‐nitrobenzyl mercaptoinosine (NBMI) and the uridine transport system of hamster fibroblasts is studied in the present work. A kinetic description of the interaction is presented. Uridine transport is inhibited in a partially competitive fashion, leaving a substantial free fraction of the transport (20–30%) virtually insensitive to increasing concentrations of inhibitor. One interpretation compatible with the kinetic and chemical properties of the system assumes that binding of the inhibitor to carriers occurs at sites different from the substrate binding sites (allosteric binding). Such a binding induces a conformational change in the carrier as manifested in a reduced affinity to the substrate and a susceptibility to inhibition by organomercurials. The alternative interpretation postulates two parallel transport systems which display distinctly different susceptibilities to NBMI and to organomercurials. Experiments performed with non‐penetrating organomercurials show that the sulfhydryl groups related either to the alleged allosteric components or to additional carriers, are located superficially on the membrane. The binding of NBMI is reversible, the affinity is extremely high (Ki = 0.15 nMolar) and the rate of reaction could probably be diffusionally limited at low concentrations of reagent (activation energy 250 cal/mole, rate k = 1.3.108 min−1. Molar−1). The high affinity properties of the probes are used to determine the number of NBMI binding sites. A value of 47,000 and 77,000 sites/cell was obtained by two separate methods.The possibility that allosteric properties are present in carrier systems are discussed in terms of current concepts of modulation of transport functions in biological membranes.
Induction of alkaline phosphatase in choriocarcinoma cells by 1‐β‐D‐arabinofuranosyl‐cytosine, mitomycin C, phleomycin, and cyclic nucleotides
Authors: Chou Janice Y. , Robinson J. C. 
Published: February 2005

AbstractAlkaline phosphatase is induced in cultured human choriocarcinoma cells by three inhibitors of DNA synthesis which alter DNA structure: 1‐β‐D‐arabinofuranosyl‐cytosine, mitomycin C, and phleomycin. No induction is observed with the inhibitors, hydroxyurea and thymidine, which do not alter DNA structure. Cyclic AMP, analogs of cyclic nucleotides, and sodium butyrate also induce alkaline phosphatase in these cells. Among the cyclic nucleotides tested, dibutyryl cyclic AMP is the best inducer, whereas dibutyryl cyclic GMP is a poor inducer.Induction of alkaline phosphatase by inhibitors of DNA synthesis or by exposure to dibutyryl cyclic AMP appears to utilize different mechanisms. Maximum induction is observed after simultaneous addition of both types of inducers at the concentrations found to be optimal for each inducer alone. Under these conditions, the induced activity is equal to or greater than the sum of the activities induced by each inducer. RNA synthesis and protein synthesis are required for induction.Dibutyryl cyclic AMP added to cultures of choriocarcinoma cells is not degraded in the culture medium, but is extensively degraded in the cells. Nevertheless, significant amounts of dibutyryl and monobutyryl cyclic AMP are found intracellularly throughout the experiment. Since the cellular uptake of dibutyryl cyclic AMP is extremely slow, the amount of butyrate released by intracellular degradation cannot account for the observed induction. Neither the rate of uptake nor the stability of dibutyryl cyclic AMP are changed by the addition of 1‐β‐D‐arabinofuranosyl‐cytosine to the culture medium. Furthermore, 1‐β‐D‐arabinofuranosyl‐cytosine inhibits the induction by sodium butyrate. The results indicate that butyrate is not the major mediator of induction by dibutyryl cyclic AMP.
A cell membrane alteration specifically induced by SV40 transformation
Authors: Lago C. , Sartorius B. , Tramontano D. , Amati P. 
Published: February 2005

AbstractTransformation of mouse 3T3 cells by SV40 results in a specific membrane modification which renders cells resistant to the killing action of the lipophilic antibiotic Amphotericin B. This alteration is under genetic cellular control and is specific for SV40 transformation since transformation with polyoma or mouse sarcoma viruses does not confer resistance to the antibiotic. Analogous resistance is induced by SV40 transformation of primary human fibroblast cells. The acquired resistance is not due to decreased binding of Amphotericin B and is partially reversed if cells are grown in the presence of cholesterol. The results are interpreted as a specific change of sterol structure of the membrane or the loss of a minor cholesterol fraction responsible for the killing action of the antibiotic.