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At least 73 records · Page 4Linked to original sources
PubMed1973

Reduction of water permeability in potato tuber slices by cyanide, ammonia, 2,4-dinitrophenol, and oligomycin and its reverse by adenosine 5'-triphosphate and cytidine 5'-triphosphate.

Five millimolar KCN reduced water permeability in 1-millimeter thick slices of potato tuber (Solanum tuberosum L.). One-tenth millimolar ATP and CTP prevented or reversed the reduced permeability. UTP and GTP were not effective. Five millimolar ammonium carbonate or 0.1 millimolar 2,4-dinitrophenol also reduced water permeability, but ATP and CTP were only partially effective in reversing the reduced permeability. Oligomycin, 5 micrograms per milliliter, reduced water permeability, and the reduction was reversed by ATP and CTP. ATP and CTP appear to be involved in maintaining the structure of water pathways into the cell.

Journal Article↗
PubMed1982

Kinetics of N-(phosphonacetyl)-L-aspartate and pyrazofurin depletion of pyrimidine ribonucleotide and deoxyribonucleotide pools and their relationship to nucleic acid synthesis in intact and permeabilized cells.

Pools of uridine triphosphate and cytidine triphosphate are greatly (90%) reduced in cultured L1210 cells exposed to N-(phosphonacetyl)-L-aspartate (PALA) or pyrazofurin; the concentration of the deoxynucleotides deoxycytidine triphosphate, deoxythymidine triphosphate, and deoxyguanosine triphosphate also decreases, but deoxyadenosine triphosphate pools are enlarged. Associated with these pool depletions is a pronounced inhibition of DNA synthesis even when pools are only moderately reduced; RNA synthesis is only slightly inhibited under these same conditions. DNA synthesis in permeabilized preparations of L1210 cells was also more sensitive than was RNA synthesis when the concentrations of ribonucleotide and deoxyribonucleotide triphosphates presented were equivalent to those found in PALA- or pyrazofurin-treated cells. The specific sensitivity to depletion of DNA precursors was also seen in protection of both DNA synthesis and growth of L1210 cells by deoxycytidine and thymidine. This supplement restored deoxycytidine triphosphate, deoxythymidine triphosphate, and deoxyguanosine triphosphate pools to normal but of course did not affect the marked depletions of uridine triphosphate and cytidine triphosphate or the less marked effect of PALA on RNA synthesis. The relative ability of PALA to reduce uridine triphosphate and cytidine triphosphate pool size in L1210 ascites and Lewis lung carcinoma in vivo correlates with the intrinsic sensitivity to this agent.

Amides↗
PubMed1997

ATP acting on P2Y receptors triggers calcium mobilization in Schwann cells at the neuroelectrocyte junction in skate.

Schwann cells are integral cellular components of the dense cholinergic presynaptic plexus (nerve plate) which innervates each electrocyte in skate electric organ. Using the Ca2+-sensitive dye fura-2, we have followed the response in these cells to various chemical challenges. In K+ depolarized nerve plates nerve terminals consistently responded with a rapid and sustained Ca2+ signal. Schwann cell responses to depolarization were rarely seen but, when observed, were always delayed in onset when compared to nerve terminal response (6-10 s later). The possibility that these responses were triggered by mediators released from nerve terminals was tested by direct application of candidate substances. Schwann cells were found to respond to adenosine triphosphate and adenosine diphosphate with a biphasic increase of intracellular Ca2+ concentration, a rapid peak response being followed in the majority of cells by a sustained plateau phase. In the absence of external Ca2+ only the transient peak response was observed. Depletion of internal Ca2+ stores with thapsigargin completely inhibited the adenosine triphosphate-stimulated rise in Schwann cell Ca2+. The response to adenosine triphosphate was concentration-dependent (EC50 2.8 microM) and was reversibly blocked by two antagonists of P2 purinoceptors: suramin and reactive blue 2. Adenosine diphosphate and 2-methylthio-adenosine triphosphate were equipotent with adenosine triphosphate and at high concentrations (100 microM) diadenosine tetraphosphate produced responses comparable to low concentrations of adenosine triphosphate. Adenosine, adenosine monophosphate, the alpha beta-methylene analogues of adenosine triphosphate and adenosine diphosphate, uridine triphosphate, cytidine triphosphate and guanosine triphosphate were without significant effect. These results show that, in skate electric organ Schwann cells, the release of Ca2+ from intracellular stores is triggered by adenosine triphosphate acting on P(2gamma) receptors and suggest that Schwann cells may be targets for synaptically-released adenosine triphosphate in the electric organ model of the neuromuscular junction.

Acetylcholine↗
PubMed1976

Isolation of a transcriptionally active chromosome from chloroplasts of Euglena gracilis.

A transcriptionally active chromosome has been isolated in highly purified form from choroplasts of Euglena gracilis, It contains chloroplast DNA, DNA-dependent RNA polymerase, and other proteins. Transcription occurs at low levels of endogenous DNA, and is indifferent to high levels of exogenous DNA. RNA chain elongation continues for several hours in vitro, and RNA chain initiation, determined by [gamma-32P]ATP incorporation, is continuous for at least 1 h in vitro. Maximal rates for RNA synthesis require only a divalent cation and the four ribonucleoside triphosphates. Apparent Km values for adenosine triphosphate, cytidine triphosphate, guanosine triphosphate, and uridine triphosphate are 4.0, 0.6, 2.5, and 2.3 muM, respectively. As would be expected for a DNA-dependent RNA polymerase, RNA synthesis is inhibited by actinomycin D. However, rifampicin and streptolydigin, inhibitors of procaryotic RNA synthesis, and alpha-amanitin, an inhibitor of eucaryotic nuclear RNA polymerases II and III, do not inhibt the RNA synthesis reaction. Heparin, which is a potent inhibitor of the initiation of RNA synthesis by a nontemplate bound RNA polymerase, also does not inhibit RNA synthesis. Isolation of transcriptionally active chromosomes should prove to be a useful method to study the mechanism of selective RNA transcription of eucaryotic chromosomes.

Aminoglycosides↗
PubMed2001

Effect of gestational age and hypoxia on activity of ribonucleic acid polymerase in fetal guinea pig brain.

OBJECTIVE: The aim of this study was to determine the effect of gestational age and hypoxia on the activity of ribonucleic acid polymerase in fetal guinea pig brain. STUDY DESIGN: Fetal cerebral cortical neuronal nuclei were isolated at 40, 50, and 60 days (term) of gestation to determine the effect of gestational age on the activity of ribonucleic acid polymerase I, II, and III. Pregnant guinea pigs at 60 days' gestation were randomly assigned to a normoxic or hypoxic group to determine the effect of hypoxia on ribonucleic acid polymerase activity. The fetal neuronal nuclei were pooled from 6 pregnant animals in each group. In the normoxic group the pregnant guinea pigs were exposed to room air before delivery. In the hypoxic group delivery occurred after the pregnant guinea pig had been exposed to 7% oxygen for 60 minutes. The fetuses were delivered by cesarean, and the fetal cerebral cortical neuronal nuclei were isolated immediately. Ribonucleic acid polymerase activity was determined with nuclei suspended in a buffer containing adenosine triphosphate, guanosine triphosphate, cytidine triphosphate, and tritiated uridine triphosphate. Dactinomycin (actinomycin D) and polydeoxyadenylic-thymidylic acid were used to determine the activity of bound and free ribonucleic acid polymerase. alpha-Amanitin was used to determine the activity of ribonucleic acid polymerase II. RESULTS: The activity of total (bound and free) ribonucleic acid polymerase I and III increased from 85.4 +/- 9.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour at 40 days' gestation to 233.3 +/- 82.1 fmol at 50 days and to 343.4 +/- 231.6 fmol at 60 days (P =.02). Total ribonucleic acid polymerase II activity increased from 19.9 +/- 6.0 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour at 40 days to 123.8 +/- 53.0 fmol at 50 days and to 200.9 +/- 77.8 fmol at 60 days (P <.01). In the term fetal guinea pig brain the activity of bound ribonucleic acid polymerase I and III decreased from 116.8 +/- 107.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 92.8 +/- 76.0 fmol in hypoxic fetal brain, a decrease of 20.5%. Free ribonucleic acid polymerase I and III activity decreased from 199.2 +/- 115.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in normoxic fetal brain to 132.0 +/- 66.4 fmol in hypoxic fetal brain, a decrease of 33.8%. Free ribonucleic acid polymerase II activity decreased from 62.4 +/- 70.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in normoxic fetuses to 13.6 +/- 9.6 fmol in hypoxic fetal brain, a decrease of 78.2%. In contrast, however, in term fetal guinea pig brain, bound ribonucleic acid polymerase II activity increased from 8.0 +/- 10.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 35.2 +/- 8.8 fmol in hypoxic fetal brain, an increase of 340% (P <.01). CONCLUSION: The activity of ribonucleic acid polymerases I, II, and III increases throughout the latter half of gestation, from 40 to 60 days, in the fetal guinea pig brain. Hypoxia in utero is associated with a decrease in ribonucleic acid polymerase I and III activity. Although hypoxia is associated with a decrease in free ribonucleic acid polymerase II activity, we observed a marked increase in bound ribonucleic acid polymerase II activity, which may represent a hypoxia-induced alteration of gene expression.

Amanitins↗
PubMed1994

Adenosine triphosphate-dependent transport of leukotriene C4 by membrane vesicles prepared from cisplatin-resistant human epidermoid carcinoma tumor cells.

BACKGROUND: Cisplatin accumulation is decreased in many cisplatin-resistant cells. An active efflux pump for cisplatin exists in cisplatin-resistant human epidermoid carcinoma cells (called KB cells). A previous study has suggested that the adenosine triphosphate (ATP)-dependent glutathione S-conjugate export pump (GS-X pump), which exports the bis-(glutathionato)-platinum (II) (GS-platinum) complex, could contribute to cellular resistance to cisplatin. PURPOSE: In this study, we examined whether the active efflux pump for cisplatin in the cisplatin-resistant KB cells is the GS-X pump and tested its activity by using an endogenous substrate, [3H]leukotriene C4 ([3H]LTC4). METHODS: Membrane vesicles were prepared from KB-3-1 (clone from parental KB cells) cells and from cisplatin-resistant KCP-4 (a mutant clone derived from KB-3-1 cells) cells. Using a filtration technique, we measured the uptake and transport of [3H]LTC4, a substrate for the GS-X pump, into membrane vesicles at 37 degrees C. RESULTS: The uptake of [3H]LTC4 in the membrane vesicles from both the KB-3-1 and KCP-4 cells was ATP-dependent. In contrast, the ATP-dependent transport of [3H]LTC4 was observed only in KCP-4 membrane vesicles but not in KB-3-1 membrane vesicles. The ATP-dependent transport was vanadate sensitive and was inhibited by GS-platinum complex but only marginally by cisplatin and glutathione and not by vincristine or verapamil. The nucleotide triphosphates, guanosine triphosphate, cytidine triphosphate, uridine triphosphate, and deoxythymidine triphosphate could be substituted for ATP but were less efficient. A nonhydrolyzable ATP analogue, adenosine 5'-(beta,gamma-methylene) triphosphate, was not effective. CONCLUSIONS: The transport of LTC4 in membrane vesicles prepared from KCP-4 cells was facilitated by an ATP-dependent pump that appeared very similar to the GS-X pump. IMPLICATIONS: Our study suggests that the GS-X pump is involved in the decreased accumulation of cisplatin in KCP-4 cells.

Adenosine Triphosphate↗
PubMed1972

The levels of soluble nucleotides in wheat aleurone tissue.

The content of soluble nucleotides in aleurone layers isolated from mature wheat (Triticum aestivum var. Olympic) grain was investigated. The most abundant nucleotides were adenosine triphosphate, uridine triphosphate, and uridine diphosphoglucose. Smaller amounts of guanosine triphosphate, cytidine triphosphate, adenosine diphosphate, and nicotinamide adenine dinucleotide were also identified. The levels of some of these nucleotides were increased after incubation of the tissue under certain conditions.Nucleotide levels were measured at intervals during incubation of aleurone layers in water. The changes observed are discussed in relation to a response by the tissue to wounding.

Journal Article↗
PubMed1987

Erythrocyte membrane microviscosity and phospholipid composition in lead workers.

The microviscosity and fluidity of erythrocyte ghost membranes from lead workers and control subjects was measured by fluorescence polarisation using the fluorophore, 1,6-diphenyl-1,3,5-hexatriene (DPH). Increased lead was associated with a significant decrease in the average microviscosity of resealed and unsealed erythrocyte membranes. Since DPH fluorescence reflects the organisation of lipids in the central core of the membrane, two aspects of phospholipid metabolism were investigated. Phospholipids were extracted from red blood cell ghost membranes and identified by high performance liquid chromatography. The ratio of phosphatidyl choline to phosphatidyl ethanolamine, an established correlate of membrane fluidity, was significantly increased in lead workers. This is attributed to the known increases in red blood cell cholesterol in lead workers and the structural incompatibility of phosphatidyl ethanolamine and cholesterol, which result in a compensatory increase of phosphatidyl choline. Erythrocyte ghost membranes from control subjects were resealed with the intermediates in phospholipid synthesis that increase with a lead inhibited decrease in red blood cell pyrimidine 5'-nucleotidase. Membrane fluidity was not modified by incubation with cytidine triphosphate, uridine triphosphate, cytidine diphosphate choline, or cytidine diphosphate ethanolamine. Alterations in the microviscosity of the lipid regions of the hydrophobic core of the erythrocyte membrane bilayer and in the phospholipid composition of the membrane may be defects which contribute to the clinical and biochemical instability of the red blood cell on exposure to lead.

Adult↗