scholarly journals Stimulation of incorporation of nucleic acid precursors into HeLa cells caused by provaline

1969 ◽  
Vol 115 (4) ◽  
pp. 823-829
Author(s):  
J. W. Watts
Keyword(s):  
Nucleic Acid ◽  
Nucleic Acids ◽  
Hela Cells ◽  
Actinomycin D ◽  
Small Extent ◽  
Low Concentrations ◽  
High Concentrations ◽  
Stimulation Of

1. The effect of proflavine and other acridines on the incorporation of precursors into the nucleic acids of HeLa cells was examined. 2. Relatively low concentrations (50μm) of proflavine completely inhibited incorporation of precursors into DNA, but allowed a small extent of incorporation into RNA. 3. Acridine-resistant incorporation into RNA was unaffected by actinomycin D at 2μg./ml. and persisted even at high concentrations (500μm) of many acridines. 4. A few combinations of acridine and precursor, notably 250μm-proflavine and [14C]adenine, caused a stimulation of incorporation. 5. The proflavine-stimulated incorporation was into alkali-stable di- and tri-nucleotides. 6. It was concluded that the effect was due to the preferential inhibition of degradation of a fraction of RNA that normally turned over, thus allowing small radioactive oligonucleotides to accumulate in the cells.

scholarly journals Adenosine 3':5'-monophosphate content and actions in the division cycle of synchronized HeLa cells.

1976 ◽  
Vol 71 (2) ◽  
pp. 515-534 ◽  
Author(s):  
C E Zeilig ◽  
R A Johnson ◽  
E W Sutherland ◽  
D L Friedman
Keyword(s):  
Cell Cycle ◽  
Cyclic Amp ◽  
Hela Cells ◽  
S Phase ◽  
Intracellular Camp ◽  
Specific Effects ◽  
Low Concentrations ◽  
High Concentrations ◽  
Camp Levels ◽  
Stimulation Of

The involvement of adenosine 3':5'-monophosphate (cAMP) in the regulation of the cell cycle was studied by determining intracellular fluctuations in cAMP levels in synchronized HeLa cells and by testing the effects of experimentally altered levels on cell cycle traverse. Cyclic AMP levels were lowest during mitosis and were highest during late G-1 or early S phase. These findings were supported by results obtained when cells were accumulated at these points with Colcemid or high levels of thymidine. Additional fluctuations in cAMP levels were observed during S phase. Two specific effects of cAMP on cell cycle traverse were found. Elevation of cAMP levels in S phase or G-2 caused arrest of cells in G-2 for as long as 10 h and lengthened M. However, once cells reached metaphase, elevation of cAMP accelerated the completion of mitosis. Stimulation of mitosis was also observed after addition of CaCl2. The specificity of the effects of cAMP was verified by demonstrating that: (a) intracellular cAMP was increased after exposure to methylisobutylxanthine (MIX) before any observed effects on cycle traverse; (b) submaximal concentrations of MIX potentiated the effects of isoproterenol; and (c) effects of MIX and isoproterenol were mimicked by 8-Br-cAMP. MIX at high concentrations inhibited G-1 traverse, but this effect did not appear to be mediated by cAMP. Isoproterenol slightly stimulated G-1 traverse and partially prevented the MIX-induced delay. Moreover, low concentrations of 8-Br-cAMP (0.10-100 muM) stimulated G-1 traverse, whereas high concentrations (1 mM) inhibited. Both of these effects were also observed with the control, Br-5'-AMP, at 10-fold lower concentrations.

Effects of endogenous calcium transport inhibitor from heart muscle on the active calcium uptake and passive calcium release properties of sarcoplasmic reticulum

1989 ◽  
Vol 67 (9) ◽  
pp. 999-1006 ◽  
Author(s):  
Njanoor Narayanan ◽  
Philip Bedard ◽  
Trilochan S. Waraich
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Heart Muscle ◽  
Calcium Release ◽  
Membrane Vesicles ◽  
Transport Inhibitor ◽  
Low Concentrations ◽  
Active Calcium ◽  
High Concentrations ◽  
Stimulation Of

In the present study, the effects of the cytosolic Ca2+ transport inhibitor on ATP-dependent Ca2+ uptake by, and unidirectional passive Ca2+ release from, sarcoplassmic reticulum enriched membrane vesicles were examined in parallel experiments to determine whether inhibitor-mediated enhancement in Ca2+ efflux contributes to inhibition of net Ca2+ uptake. When assays were performed at pH 6.8 in the presence of oxalate, low concentrations (<100 μg/mL) of the inhibitor caused substantial inhibition of Ca2+ uptake by SR (28–50%). At this pH, low concentrations of the inhibitor did not cause enhancement of passive Ca2+ release from actively Ca2+-loaded sarcoplasmic reticulum. Under these conditions, high concentrations (>100 μg/mL) of the inhibitor caused stimulation of passive Ca2+ release but to a much lesser extent when compared with the extent of inhibition of active Ca2+ uptake (i.e., twofold greater inhibition of Ca2+ uptake than stimulation of Ca2+ release). When Ca2+ uptake and release assays were carried out at pH 7.4, the Ca2+ release promoting action of the inhibitor became more pronounced, such that the magnitude of enhancement in Ca2+ release at varying concentrations of the inhibitor (20–200 μg/mL) was not markedly different from the magnitude of inhibition of Ca2+ uptake. In the absence of oxalate in the assay medium, inhibition of Ca2+ uptake was observed at alkaline but not acidic pH. These findings imply that the inhibition of Ca2+ uptake observed at pH 6.8 is mainly due to decrease in the rate of active Ca2+ transport into the membrane vesicles rather than stimulation of passive Ca2+ efflux; at alkaline pH (pH 7.4), enhanced Ca2+ efflux contributes substantially, if not exclusively, to the decrease in Ca2+ uptake observed in the presence of the inhibitor. It is suggested that if the cytosolic inhibitor has actions similar to those observed in vitro in intact cardiac muscle, acid–base status of the intracellular fluid would be a major factor influencing the nature of its effects (inhibition of Ca2+ uptake or stimulation of Ca2+ release) on transmembrane Ca2+ fluxes across the sarcoplasmic reticulum.Key words: sarcoplasmic reticulum, Ca2+ uptake, Ca2+ release, endogenous inhibitor, heart muscle.

scholarly journals Biphasic Dose–Response Induced by PCB150 and PCB180 in HeLa Cells and Potential Molecular Mechanisms

Dose-Response ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 155932582091004
Author(s):  
Ainy Zehra ◽  
Muhammad Zaffar Hashmi ◽  
Abdul Majid Khan ◽  
Tariq Malik ◽  
Zaigham Abbas
Keyword(s):  
Hela Cells ◽  
Molecular Mechanisms ◽  
Dependent Manner ◽  
Genotoxic Effects ◽  
Species Formation ◽  
Low Concentrations ◽  
Extracellular Signal ◽  
High Concentrations ◽  
High Doses ◽  
Dose Dependent

The polychlorinated biphenyls (PCBs) are persistent and their dose-dependent toxicities studies are not well-established. In this study, cytotoxic and genotoxic effects of PCB150 and PCB180 in HeLa cells were studied. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated that the cell proliferation was stimulated at low doses (10−3 and 10−2 µg/mL for 12, 24, 48, and 72 hours) and inhibited at high doses (10 and 15 µg/mL for 24, 48, and 72 hours) for both PCBs. Increase in reactive oxygen species formation was observed in the HeLa cells in a time- and dose-dependent manner. Malondialdehyde and superoxide dismutase showed increased levels at high concentrations of PCBs over the time. Glutathione peroxidase expression was downregulated after PCBs exposure, suggested that both PCB congeners may attributable to cytotoxicity. Comet assay elicited a significant increase in genotoxicity at high concentrations of PCBs as compared to low concentrations indicating genotoxic effects. PCB150 and PCB180 showed decrease in the activity of extracellular signal–regulated kinase 1/2 and c-Jun N-terminal kinase at high concentrations after 12 and 48 hours. These findings may contribute to understanding the mechanism of PCBs-induced toxicity, thereby improving the risk assessment of toxic compounds in humans.

Effects of cholera toxin and isobutylmethylxanthine on growth of human fibroblasts

1986 ◽  
Vol 251 (2) ◽  
pp. C238-C246 ◽  
Author(s):  
B. Espinoza ◽  
W. Wharton
Keyword(s):  
Cholera Toxin ◽  
Human Fibroblasts ◽  
Phosphodiesterase Inhibitor ◽  
Serum Starvation ◽  
Final Density ◽  
Low Concentrations ◽  
High Concentrations ◽  
Dose Dependent Decrease ◽  
Dose Dependent ◽  
Stimulation Of

Cholera toxin produced a dose-dependent decrease in the restimulation of G0/G1 traverse in density-arrested human fibroblasts but did not inhibit the stimulation of cells arrested in G0 after serum starvation at low density. In addition, cholera toxin did not inhibit the proliferation of sparse logarithmically growing human fibroblasts, even when low concentrations of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) were also present. However, the final density to which sparse cells grew was limited by cholera toxin, when added either alone or together with low concentrations of IBMX. In contrast, high concentrations of the phosphodiesterase inhibitor alone produced a profound inhibition in the growth of sparse human fibroblasts. IBMX produced an inhibition both in the G1 and in the G2 phases of the cell cycle by a mechanism(s) that was not related to the magnitude of the increases in adenosine 3',5'-cyclic monophosphate concentrations.

The reaction of the psoralens with deoxyribonucleic acid

1984 ◽  
Vol 17 (1) ◽  
pp. 1-44 ◽  
Author(s):  
John E. Hearst ◽  
Stephen T. Isaacs ◽  
David Kanne ◽  
Henry Rapoport ◽  
Kenneth Straub
Keyword(s):  
Natural Selection ◽  
Nucleic Acid ◽  
Nucleic Acids ◽  
Chemical Modification ◽  
Deoxyribonucleic Acid ◽  
Molecular Level ◽  
Virus Particles ◽  
Cross Links ◽  
High Concentrations

Psoralen photochemistry is specific for nucleic acids and is better understood at the molecular level than are all other methods of chemical modification of nucleic acids. These compounds are used both for in vivo structure analysis and for photochemotherapy since they easily penetrate both cells and virus particles. Apparently, natural selection has selected for membrane and virus penetrability during the evolution of these natural products. Most cells are unaffected by relatively high concentrations of psoralens in the absence of ultraviolet light, and the metabolites of the psoralens have thus far not created a problem. Finally, psoralens form both monoadduct and cross-links in nucleic acid helices, the yield of each being easily controlled by the conditions used during the photochemistry.

Opposing actions of the enantiomers of BAY-K-8644 on calcium currents and ACTH secretion in clonal pituitary corticotrophs

1987 ◽  
Vol 65 (12) ◽  
pp. 2409-2414 ◽  
Author(s):  
J. F. MacDonald ◽  
Z. Miljkovic ◽  
S. Heisler
Keyword(s):  
Bay K 8644 ◽  
Calcium Currents ◽  
Similar Relationship ◽  
Acth Secretion ◽  
Calcium Dependent ◽  
Low Concentrations ◽  
Voltage Dependent ◽  
High Concentrations ◽  
Opposing Effects ◽  
Stimulation Of

BAY-K-8644 in low concentrations is known to stimulate, and in higher concentrations, to depress calcium-dependent ACTH secretion from mouse clonal (tumor) pituitary corticotrophs, AtT-20/D16-16 (AtT-20). In the present study, voltage-dependent inward calcium currents in these cells were potentiated by low concentrations of this compound and depressed by higher concentrations consistent with its actions on ACTH secretion. A similar relationship was demonstrated for a different but related compound, CGP 28 392. Each of BAY-K-8644's enantiomers, BAY-R(−)5417 and BAY-R(+)4407, had opposing effects upon these inward calcium currents and ACTH secretion. The (+)isomer antagonized both inward calcium currents and ACTH secretion. In contrast, the (−)enantiomer was responsible for the stimulatory effects of BAY-K-8644. Nevertheless, some antagonistic properties were noted with high concentrations of this latter enantiomer. The stimulation of ACTH secretion in AtT-20 cells by low concentrations of BAY-K-8644 can be attributed to a potentiation of voltage-activated calcium currents by one of its enantiomers, BAY-R-(−)5417. In contrast, the depression of secretion that occurs at higher concentrations is likely to be the result of the reduction of these currents by the other enantiomer (BAY-R(+)4407).

scholarly journals Stimulation of hepatic biogenesis of sterols on administration of adenosine compounds

1976 ◽  
Vol 154 (3) ◽  
pp. 639-645 ◽  
Author(s):  
G. S Rao ◽  
R George ◽  
T. Ramasarma
Keyword(s):  
Fatty Acids ◽  
Food Intake ◽  
Regulatory Role ◽  
Liver Slices ◽  
Low Concentrations ◽  
High Concentrations ◽  
Partial Deficiency ◽  
Coa Reductase ◽  
Stimulation Of

1. Re-feeding starved rats increased the biogenesis of sterols in livers, with highest activity at 6h after the start of food intake. 2. Complete deficiency of protein or fat and partial deficiency of carbohydrate in the diet had no effect on sterol biogenesis. 3. Glucose, citrate or pyruvate, when administered intraperitoneally to starved rats, stimulated the biogenesis of sterols only at high concentrations. 4. ATP given intraperitoneally at low concentrations (10mg/rat) stimulated biogenesis of sterols, but not of fatty acids, from [1-14C]acetate. This effect was also obtained with other adenosine compounds, but not with adenine or guanosine. 5. Administration of adenosine compounds to starved rats also increased the incorporation of [1-14C]acetate into sterols in liver slices and also the activity of microsomal 3-hydroxy-3-methylglutaryl-CoA reductase. The results suggest a regulatory role for adenosine compounds in the hepatic biogenesis of isoprenoid compounds.

Potentiation of Adrenaline-Induced Platelet Aggregation by Angiotensin II

1985 ◽  
Vol 54 (03) ◽  
pp. 717-720 ◽  
Author(s):  
Yu-An Ding ◽  
D Euan MacIntyre ◽  
Christopher J Kenyon ◽  
Peter F Semple
Keyword(s):  
Platelet Aggregation ◽  
Angiotensin Ii ◽  
Human Platelet ◽  
Inhibitory Effect ◽  
Facilitatory Effect ◽  
Ang Ii ◽  
Human Platelet Aggregation ◽  
Low Concentrations ◽  
High Concentrations ◽  
Stimulation Of

SummaryThe effects of angiotensin II (ANG II) alone and in combination with other agonists on human platelet aggregation, thromboxane B2 (TxB2) and cytosolic [Ca2+]i were investigated. ANG II (10™11 - 10™7 M) alone had no direct effect on aggregation, TxB2 production or [Ca2+]i after short- (<2 min) or longterm (30 min) incubation. In contrast, low concentrations of ANG II (10™11 M) enhanced adrenaline-induced platelet aggregation but high concentrations (10™7 M) had an inhibitory effect. Moreover, ANG II (10™11 - 10™7 M) augmented platelet responses to the TxA2 mimetic, U44069. Pretreatment of platelets with flurbiprofen abolished this facilitatory effect of ANG II on adrenaline- but not on U44069-induced platelet aggregation. These results suggest that ANG II stimulation of agonist-induced platelet activation may be due to potentiation of the effects rather than the synthesis of TxA2

The alteration of mitotic events by ionophore A23187 and carbonyl cyanide n-chlorophenylhydrazone

1985 ◽  
Vol 75 (1) ◽  
pp. 347-355
Author(s):  
M.L. Ziegler ◽  
J.E. Sisken ◽  
S. Vedbrat
Keyword(s):  
Oxidative Phosphorylation ◽  
Intracellular Calcium ◽  
Calcium Ions ◽  
Hela Cells ◽  
Cytosolic Calcium ◽  
Ionophore A23187 ◽  
Chromosome Movement ◽  
Low Concentrations ◽  
Carbonyl Cyanide ◽  
Stimulation Of

A large quantity of published work indicates that calcium ions may be involved in the regulation of mitotic events and recent reports suggest that the onset of chromosome movement is dependent upon a transient increase in free cytosolic calcium ions. In this paper we examine the effects of two agents known to perturb intracellular calcium pools on mitosis in HeLa cells. These were the calcium-selective ionophore A23187 and carbonyl cyanide n-chlorophenylhydrazone (CCCP), which is a protonophoric inhibitor of oxidative phosphorylation. Owing to a stimulation of glycolysis, the latter agent does not decrease intracellular ATP in HeLa but does cause mitochondria to release calcium ions. Our data show that, at low concentrations, both agents prolong metaphase but differ in their effects on anaphase and cytokinesis. Studies with chlorotetracycline, a commonly used probe for membrane-associated calcium, verify that these agents do affect calcium pools under the conditions of our experiments. The data presented are consistent with the idea that increased cytosolic calcium levels can directly or indirectly affect mitotic events but, contrary to other suggestions, cause a prolongation of metaphase, i.e. they delay the onset of chromosome movement.

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