scholarly journals The pathway of adenine nucleotide catabolism and its control in isolated rat hepatocytes subjected to anoxia

1982 ◽  
Vol 202 (1) ◽  
pp. 117-123 ◽  
Author(s):  
Marie-Françoise Vincent ◽  
Georges Van Den Berghe ◽  
Henri-Géry Hers
Keyword(s):  
Uric Acid ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Urate Oxidase ◽  
Amp Deaminase ◽  
Isolated Rat Hepatocytes ◽  
Adenine Nucleotide Pool ◽  
Glycogen Stores ◽  
Isolated Rat

1. The breakdown of the adenine nucleotide pool provoked by the replacement of the O2/CO2 gas phase by N2/CO2 was studied in isolated rat hepatocytes with the purpose of defining the pathway of the catabolism of AMP in anoxic conditions. 2. Approx. 40% of the adenine nucleotide pool was lost after 40–60 min of anoxia. In hepatocytes from fed rats there was a slow disappearance of ATP. This is explained by the presence of glycogen stores, allowing the generation of ATP by anaerobic glycolysis. In hepatocytes from 24h-starved rats, ATP almost completely disappeared within 5 min, and was partly replaced by an accumulation of AMP. This indicates that another mechanism protects the adenine nucleotide pool in the starved state. In both conditions, the loss of adenine nucleotides was mainly accounted for by an accumulation of uric acid, owing to the oxygen-dependence of urate oxidase. 3. Incubation of the hepatocytes before the suppression of O2 with coformycin at concentrations known to inhibit selectively adenosine deaminase did not result in an accumulation of adenosine and did not influence the formation of uric acid. This indicates that the degradation of AMP does not proceed by way of 5′-nucleotidase under these conditions. In the presence of coformycin at concentrations which are inhibitory to AMP deaminase, however, the formation of uric acid was nearly suppressed, demonstrating that the initial degradation of AMP was catalysed by the latter enzyme. 4. The accumulation of AMP in the starved state can be explained by the pronounced decrease in ATP, the major stimulator of AMP deaminase, and the enhanced increase in Pi, one of its physiological inhibitors. The modifications of these effectors can also explain the increased inhibition of the cytoplasmic 5′-nucleotidase, shown by the accumulation of IMP in the absence of coformycin, in hepatocytes from starved rats. 5. Reoxygenation of the hepatocytes after 20 min of anoxia induced a prompt regeneration of ATP, which reached concentrations equal to the pre-existing concentration of AMP. 6. No explanation was found for the accumulation of IMP observed after preincubation of the hepatocytes with 0.1μm-coformycin, since the activities of the IMP-metabolizing enzymes were not influenced by this inosine analogue.

scholarly journals Purine catabolism in isolated rat hepatocytes. Influence of coformycin

1980 ◽  
Vol 188 (3) ◽  
pp. 913-920 ◽  
Author(s):  
Georges Van Den Berghe ◽  
Françoise Bontemps ◽  
Henri-Géry Hers
Keyword(s):  
High Speed ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Amp Deaminase ◽  
Purine Nucleotides ◽  
Isolated Rat Hepatocytes ◽  
Adenine Nucleotide Pool ◽  
Isolated Rat

1. The catabolism of purine nucleotides was investigated by both chemical and radiochemical methods in isolated rat hepatocytes, previously incubated with [14C]adenine. The production of allantoin reached 32±5nmol/min per g of cells (mean±s.e.m.) and as much as 30% of the radioactivity incorporated in the adenine nucleotides was lost after 1h. This rate of degradation is severalfold in excess over values previously reported to occur in the liver in vivo. An explanation for this enhancement of catabolism may be the decrease in the concentration of GTP. 2. In a high-speed supernatant of rat liver, adenosine deaminase was maximally inhibited by 0.1μm-coformycin. The activity of AMP deaminase, measured in the presence of its stimulator ATP in the same preparation, as well as the activity of the partially purified enzyme, measured after addition of its physiological inhibitors GTP and Pi, required 50μm-coformycin for maximal inhibition. 3. The production of allantoin by isolated hepatocytes was not influenced by the addition of 0.1μm-coformycin, but was decreased by concentrations of coformycin that were inhibitory for AMP deaminase. With 50μm-coformycin the production of allantoin was decreased by 85% and the formation of radioactive allantoin from [14C]adenine nucleotides was completely suppressed. 4. In the presence of 0.1μm-coformycin or in its absence, the addition of fructose (1mg/ml) to the incubation medium caused a rapid degradation of ATP, without equivalent increase in ADP and AMP, followed by transient increases in IMP and in the rate of production of allantoin; adenosine was not detectable. In the presence of 50μm-coformycin, the fructose-induced breakdown of ATP was not modified, but the depletion of the adenine nucleotide pool proceeded much more slowly and the rate of production of allantoin increased only slightly. No rise in IMP concentration could be detected, but AMP increased manyfold and reached values at which a participation of soluble 5′-nucleotidase in the catabolism of adenine nucleotides is most likely. 5. These results are in agreement with the hypothesis that the formation of allantoin is controlled by AMP deaminase. They constitute further evidence that 5′-nucleotidase is inactive on AMP, unless the concentration of this nucleotide rises to unphysiological values.

Fructose-induced adenine nucleotide catabolism in isolated rat hepatocytes

1977 ◽  
Vol 55 (12) ◽  
pp. 1237-1240 ◽  
Author(s):  
Camilla M. Smith ◽  
Liisa M. Rovamo ◽  
Kari O. Raivio
Keyword(s):  
Adenosine Deaminase ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Amp Deaminase ◽  
Isolated Rat Hepatocytes ◽  
Previous Hypothesis ◽  
Adenine Nucleotide Pool ◽  
Isolated Rat

The mechanism of fructose-induced nucleotide catabolism was studied using isolated rat hepatocytes in which the adenine nucleotide pool was prelabelled with [14C]adenine. Incubation of these cells with fructose caused a rapid depletion of the adenine nucleotides and a corresponding increase in allantoin. There was no accumulation of radioactivity in adenosine in the presence or absence of the adenosine deaminase inhibitor 9-erythro-(2-hydroxy-3-nonyl)adenine. This confirms the previous hypothesis that fructose-induced adenine nucleotide catabolism occurs by way of AMP deaminase (AMP amino-hydrolase, EC 3.5.4.6).

Purine metabolism in isolated rat hepatocytes

1977 ◽  
Vol 55 (11) ◽  
pp. 1134-1139 ◽  
Author(s):  
Camilla M. Smith ◽  
Liisa M. Rovamo ◽  
Martti P. Kekomäki ◽  
Kari O. Raivio
Keyword(s):  
Cell Function ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Purine Metabolism ◽  
Nucleotide Synthesis ◽  
Isolated Rat Hepatocytes ◽  
Collagenase Perfusion ◽  
Adenine Nucleotide Pool

The metabolism of adenine, hypoxanthine, guanine, and adenosine was studied in rat liver cell suspensions, prepared by collagenase perfusion. Oxygen supply was a critical variable in the preparation and subsequent incubation of the cells, as judged on the basis of the ratio of radioactivity in ATP to that in ADP after incubation with [14C]adenine. This ratio is suggested as an additional criterion of cell function. Adenine nucleotides synthesized from [14C]adenine were slowly catabolized to allantoin, with little incorporation of radioactivity into other purine compounds. [14C]Adenine is thus suitable for prelabelling the adenine nucleotide pool. [14C]Guanine and [14C]hypoxanthine were rapidly catabolized to allantoin, whereas nucleotide synthesis was low. [14C]Adenosine was initially phosphorylated and deaminated at about equal rates, but with continued incubation catabolic products predominated. Isolated hepatocytes were found suitable for studies of purine metabolism, in which the liver has important functions for the whole organism.

scholarly journals The mechanism by which adenosine decreases gluconeogenesis from lactate in isolated rat hepatocytes

1987 ◽  
Vol 246 (2) ◽  
pp. 449-454 ◽  
Author(s):  
A Lavoinne ◽  
H A Buc ◽  
S Claeyssens ◽  
M Pinosa ◽  
F Matray
Keyword(s):  
Ketone Body ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Adenosine Kinase ◽  
Isolated Rat Hepatocytes ◽  
Adenosine Deaminase 2 ◽  
Body Production ◽  
Gluconeogenic Substrates ◽  
Isolated Rat ◽  
Stimulation Of

Incubation of hepatocytes from 24 h-starved rats in the presence of 0.5 mM-adenosine decreased gluconeogenesis from lactate, but not from alanine. The inhibition of gluconeogenesis was associated with a stimulation of ketone-body production and an inhibition of pyruvate oxidation. These metabolic changes were suppressed in the presence of iodotubercidin (an inhibitor of adenosine kinase), but were reinforced in the presence of deoxycoformycin (an inhibitor of adenosine deaminase); 2-chloroadenosine induced no change in gluconeogenesis from lactate. These data indicate that the inhibition of gluconeogenesis by adenosine probably results from its conversion into adenine nucleotides. In the presence of lactate or pyruvate, but not with alanine or asparagine, this conversion resulted in a decrease in the [ATP]/[ADP] ratio in both mitochondrial and cytosolic compartments. Adenosine decreased the Pi concentration with all gluconeogenic substrates.

scholarly journals Effect of adenosine and inosine on ureagenesis in hepatocytes

1987 ◽  
Vol 245 (2) ◽  
pp. 371-374 ◽  
Author(s):  
R Guinzberg P ◽  
I Laguna ◽  
A Zentella ◽  
R Guzman ◽  
E Piña
Keyword(s):  
Uric Acid ◽  
Rat Hepatocytes ◽  
Physiological Significance ◽  
Isolated Rat Hepatocytes ◽  
Dose Dependent ◽  
Isolated Rat ◽  
Stimulation Of

Adenosine and inosine produced a dose-dependent stimulation of ureagenesis in isolated rat hepatocytes. Hypoxanthine, xanthine and uric acid were without effect. Half-maximally effective concentrations were 0.08 microM for adenosine and 5 microM for inosine. Activation of ureagenesis by both nucleosides had the following characteristics: (a) it was observed with either glutamine or (NH4)2CO3, provided that glucose was present; (b) it was not detected when glucose was replaced by lactate plus oleate; (c) it was mutually antagonized by glucagon, but not by adrenaline; and (d) it was dependent on Ca2+. We suggest that the action of adenosine and inosine on ureagenesis might be of physiological significance.

scholarly journals Homocysteine enhances the inhibitory effect of extracellular adenosine on the synthesis of proteins in isolated rat hepatocytes

1995 ◽  
Vol 310 (3) ◽  
pp. 893-896 ◽  
Author(s):  
S Tinton ◽  
P Buc-Calderon
Keyword(s):  
Protein Synthesis ◽  
Kinase Inhibitor ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Adenosine Kinase ◽  
Isolated Rat Hepatocytes ◽  
Extracellular Adenosine ◽  
Inhibition Of Protein Synthesis ◽  
Isolated Rat

Previous work has shown that extracellular adenosine inhibits the incorporation of radiolabelled leucine into proteins in isolated rat hepatocytes [Tinton, Lefebvre, Cousin and Buc Calderon (1993) Biochim. Biophys. Acta 1176, 1-6]. In this study, we investigated whether its metabolism into adenine nucleotides, inosine or S-adenosylhomocysteine (AdoHcy) is required to induce such an impairment. Incubation of isolated hepatocytes in the presence of adenosine at 0.5 or 1 mM reduces the synthesis of proteins by about 45% after 120 min of incubation. Such an inhibition occurred without cell lysis and was not modified by adding the adenosine kinase inhibitor 5-iodotubercidin (15 microM) or the adenosine deaminase inhibitor coformycin (0.1 microM). It is therefore unlikely that the anabolic and catabolic pathways of adenosine are involved in the inhibition of protein synthesis. Adenosine (1 mM) increased the level of AdoHcy and S-adenosylmethionine by 20- and 5-fold respectively after 60 min of incubation and reduced the methylation index. These events as well as the inhibition of protein synthesis were strongly enhanced in the presence of L-homocysteine (2 mM). It is therefore concluded that the metabolism of adenosine into AdoHcy, which is known to be a potent inhibitor of cellular methylation reactions, may play an important role in the control of translation.

Nuclear Accumulation of G-Actin in Isolated Rat Hepatocytes by Adenine Nucleotides

1997 ◽  
Vol 240 (3) ◽  
pp. 697-700 ◽  
Author(s):  
Irma Meijerman ◽  
W.Marty Blom ◽  
Hans J.G.M. de Bont ◽  
Gerard J. Mulder ◽  
J.Fred Nagelkerke
Keyword(s):  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Nuclear Accumulation ◽  
Isolated Rat Hepatocytes ◽  
Isolated Rat

scholarly journals AMP deaminase as a cell-age marker in transient erythroblastopenia of childhood and its role in the adenylate economy of erythrocytes

Blood ◽  
1989 ◽  
Vol 74 (6) ◽  
pp. 2161-2165 ◽  
Author(s):  
DE Paglia ◽  
WN Valentine ◽  
M Nakatani ◽  
RA Brockway
Keyword(s):  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Direct Consequence ◽  
Nucleotide Metabolism ◽  
Amp Deaminase ◽  
Age Related ◽  
Cell Age ◽  
Reliable Marker ◽  
Salvage Pathways ◽  
Adenine Nucleotide Pool

Abstract Erythrocytes from 11 patients with presumptive diagnoses of transient erythroblastopenia of childhood were evaluated retrospectively (six) or prospectively (five) for a possible relationship between erythrocyte adenosine 5′-monophosphate aminohydrolase, adenylic acid deaminase (AMP deaminase) activity and intracellular concentrations of adenine nucleotides. Older red blood cell (RBC) cohorts in these patients consistently exhibited significantly decreased activities of AMP deaminase (approximately 5% to 70% of normal control mean) in association with increased concentrations (up to threefold) of adenosine triphosphate (ATP) and total adenine nucleotides. We postulate that the latter is a direct consequence of the former, since diminishing AMP deaminase activity in aging cells should reduce the drain on the adenine nucleotide pool imposed by irreversible deamination of AMP to inosine 5′-monophosphate. Consistent reductions in AMP deaminase activity indicate that this enzyme should also serve as a reliable marker of mean RBC age useful in diagnostic confirmation of transient erythroblastopenia. The observed increases in ATP and total adenine nucleotides in older RBCs require a reevaluation of the traditional view that age-related losses of these compounds mediate the ultimate demise of senescent erythrocytes. Similar alterations in the balance of degradative and salvage pathways in RBC nucleotide metabolism may also underlie certain cases of so-called “high ATP syndrome.”

scholarly journals AMP-activated protein kinase-independent inhibition of hepatic mitochondrial oxidative phosphorylation by AICA riboside

2007 ◽  
Vol 404 (3) ◽  
pp. 499-507 ◽  
Author(s):  
Bruno Guigas ◽  
Nellie Taleux ◽  
Marc Foretz ◽  
Dominique Detaille ◽  
Fabrizio Andreelli ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Oxidative Phosphorylation ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Cellular Respiration ◽  
Mitochondrial Oxidative Phosphorylation ◽  
Isolated Rat Hepatocytes ◽  
Amp Activated Protein Kinase ◽  
Isolated Rat ◽  
In Cells

AICA riboside (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside) has been extensively used in cells to activate the AMPK (AMP-activated protein kinase), a metabolic sensor involved in cell energy homoeostasis. In the present study, we investigated the effects of AICA riboside on mitochondrial oxidative; phosphorylation. AICA riboside was found to dose-dependently inhibit the oligomycin-sensitive JO2 (oxygen consumption rate) of isolated rat hepatocytes. A decrease in Pi (inorganic phosphate), ATP, AMP and total adenine nucleotide contents was also observed with AICA riboside concentrations >0.1 mM. Interestingly, in hepatocytes from mice lacking both α1 and α2 AMPK catalytic subunits, basal JO2 and expression of several mitochondrial proteins were significantly reduced compared with wild-type mice, suggesting that mitochondrial biogenesis was perturbed. However, inhibition of JO2 by AICA riboside was still present in the mutant mice and thus was clearly not mediated by AMPK. In permeabilized hepatocytes, this inhibition was no longer evident, suggesting that it could be due to intracellular accumulation of Z nucleotides and/or loss of adenine nucleotides and Pi. ZMP did indeed inhibit respiration in isolated rat mitochondria through a direct effect on the respiratory-chain complex I. In addition, inhibition of JO2 by AICA riboside was also potentiated in cells incubated with fructose to deplete adenine nucleotides and Pi. We conclude that AICA riboside inhibits cellular respiration by an AMPK-independent mechanism that likely results from the combined intracellular Pi depletion and ZMP accumulation. Our data also demonstrate that the cellular effects of AICA riboside are not necessarily caused by AMPK activation and that their interpretation should be taken with caution.

scholarly journals Adenine nucleotide metabolism in isolated chicken hepatocytes

1987 ◽  
Vol 242 (2) ◽  
pp. 551-558 ◽  
Author(s):  
J Spychała ◽  
G Van den Berghe
Keyword(s):  
Uric Acid ◽  
Metabolic Flux ◽  
De Novo ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Total Concentration ◽  
Nucleotide Metabolism ◽  
Adenosine Kinase ◽  
Adenine Nucleotide Metabolism ◽  
Adenine Nucleotide Pool

The turnover of the adenine nucleotide pool, the pathway of the degradation of AMP and the occurrence of recycling of adenosine were investigated in isolated chicken hepatocytes, in which the adenylates had been labelled by prior incubation with [14C]adenine. Under physiological conditions, 85% of the IMP synthesized by the ‘de novo’ pathway (approx. 37 nmol/min per g of cells) was catabolized directly via inosine into uric acid, and 14% was converted into adenine nucleotides. The latter were found to turn over at the rate of approx. 5 nmol/min per g of tissue. Inhibition of adenosine deaminase by 1 microM-coformycin had no effect on the formation of labelled uric acid, indicating that the initial degradation of AMP proceeds by way of deamination rather than dephosphorylation. Inhibition of adenosine kinase by 100 microM-5-iodotubercidin resulted in a loss of labelled ATP, demonstrating that adenosine is normally formed from AMP but is recycled. Unexpectedly, 5-iodotubercidin did not decrease the total concentration of ATP, indicating that the loss of adenylates caused by inhibition of adenosine kinase was nearly completely compensated by formation of AMP de novo. Anoxia induced a greatly increased catabolism of the adenine nucleotide pool, which proceeded in part by dephosphorylation of AMP. On reoxygenation, the formation of AMP de novo was increased 8-fold as compared with normoxic conditions. The latter results indicate the existence of adaptive mechanisms in chick liver allowing, when required, channelling of the metabolic flux through the ‘de novo’ pathway, away from the uricotelic catabolic route, into the synthesis of adenine nucleotides.

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