Rat cardiac myocyte adenosine transport and metabolism

1987 ◽  
Vol 252 (1) ◽  
pp. H54-H63 ◽  
Author(s):  
D. A. Ford ◽  
M. J. Rovetto
Keyword(s):  
Metabolic Flux ◽  
Cardiac Myocyte ◽  
Ventricular Myocytes ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Nucleotide Metabolism ◽  
Adenosine Kinase ◽  
Maximal Velocity ◽  
Extracellular Adenosine ◽  
Minimum Estimate

Based on the importance of myocardial adenosine and adenine nucleotide metabolism, the adenosine salvage pathway in ventricular myocytes was studied. Accurate estimates of transport rates, separate from metabolic flux, were determined. Adenosine influx was constant between 3 and 60 s. Adenosine metabolism maintained intracellular adenosine concentrations less than 10% of the extracellular adenosine concentrations and thus unidirectional influx could be measured. Myocytes transported adenosine via saturable [Michaelis constant = 6.2 +/- 2.1 microM and maximal velocity (Vmax) = 9.58 +/- 0.98 X 10(-1) pmol X mg protein-1 X s-1] and nonsaturable (rate constant = 1.8 X 10(-3)/s) processes. A minimum estimate of the Vmax of myocytic adenosine kinase (2 pmol X mg protein-1 X s-1) indicated the saturable component of adenosine influx was independent of adenosine kinase activity. Saturable transport was inhibited by nitrobenzylthioinosine and verapamil (inhibitor constant = 17 +/- 5 microM). Extracellular adenosine taken up by myocytes was rapidly phosphorylated to adenine nucleotides. Not all extracellular adenosine, though, was phosphorylated on entering myocytes, since free, as opposed to protein-bound, intracellular adenosine was detected after digitonin extraction of cells in the presence of 1 mM ethylene-diaminetetraacetic acid.

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.

The Platelet of the Newborn Infant – Adenine Nucleotide Metabolism and Release

1980 ◽  
Vol 43 (02) ◽  
pp. 099-103 ◽  
Author(s):  
J M Whaun ◽  
P Lievaart ◽  
Keyword(s):  
Newborn Infant ◽  
Adenine Nucleotide ◽  
Platelet Rich Plasma ◽  
Adenine Nucleotides ◽  
Newborn Infants ◽  
Specific Radioactivity ◽  
Nucleotide Metabolism ◽  
Breakdown Product ◽  
Term Infants ◽  
Adenine Nucleotide Metabolism

SummaryBlood from normal full term infants, mothers and normal adults was collected in citrate. Citrated platelet-rich plasma was prelabelled with 3H-adenine and reacted with release inducers, collagen and adrenaline. Adenine nucleotide metabolism, total adenine nucleotide levels and changes in sizes of these pools were determined in platelets from these three groups of subjects.At rest, the platelet of the newborn infant, compared to that of the mother and normal adult, possessed similar amounts of adenosine triphosphate (ATP), 4.6 ± 0.2 (SD), 5.0 ± 1.1, 4.9 ± 0.6 µmoles ATP/1011 platelets respectively, and adenosine diphosphate (ADP), 2.4 ± 0.7, 2.8 ± 0.6, 3.0 ± 0.3 umoles ADP/1011 platelets respectively. However the marked elevation of specific radioactivity of ADP and ATP in these resting platelets indicated the platelet of the neonate has decreased adenine nucleotide stores.In addition to these decreased stores of adenine nucleotides, infant platelets showed significantly impaired release of ADP and ATP on exposure to collagen. The release of ADP in infants, mothers, and other adults was 0.9 ± 0.5 (SD), 1.5 ± 0.5, 1.5 ± 0.1 umoles/1011 platelets respectively; that of ATP was 0.6 ± 0.3, 1.0 ± 0.1,1.3 ± 0.2 µmoles/1011 platelets respectively. With collagen-induced release, platelets of newborn infants compared to those of other subjects showed only slight increased specific radioactivities of adenine nucleotides over basal levels. The content of metabolic hypoxanthine, a breakdown product of adenine nucleotides, increased in both platelets and plasma in all subjects studied.In contrast, with adrenaline as release inducer, the platelets of the newborn infant showed no adenine nucleotide release, no change in total ATP and level of radioactive hypoxanthine, and minimal change in total ADP. The reason for this decreased adrenaline reactivity of infant platelets compared to reactivity of adult platelets is unknown.Infant platelets may have different membranes, with resulting differences in regulation of cellular processes, or alternatively, may be refractory to catecholamines because of elevated levels of circulating catecholamines in the newborn period.

scholarly journals L-Arginine Intake Effect on Adenine Nucleotide Metabolism in Rat Parenchymal and Reproductive Tissues

2012 ◽  
Vol 2012 ◽  
pp. 1-4 ◽  
Author(s):  
G. Kocic ◽  
J. Nikolic ◽  
T. Jevtovic-Stoimenov ◽  
D. Sokolovic ◽  
H. Kocic ◽  
...  
Keyword(s):  
Adenosine Deaminase ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Tissue Growth ◽  
Nucleotide Metabolism ◽  
Amp Deaminase ◽  
Male Impotence ◽  
Adenine Nucleotide Metabolism ◽  
Adenosine Concentration ◽  
Male Wistar Rats

L-arginine is conditionally essetcial amino acid, required for normal cell growth, protein synthesis, ammonia detoxification, tissue growth and general performance, proposed in the treatment of men sterility and prevention of male impotence. The aim of the present paper was to estimate the activity of the enzymes of adenine nucleotide metabolism:5′-nucleotidase (5′-NU), adenosine deaminase (ADA), AMP deaminase, and xanthine oxidase (XO), during dietary intake of L-arginine for a period of four weeks of male Wistar rats. Adenosine concentration in tissues is maintained by the relative activities of the adenosine-producing enzyme,5′-NU and the adenosine-degrading enzyme-ADA adenosine deaminase. Dietary L-arginine intake directed adenine nucleotide metabolism in liver, kidney, and testis tissue toward the activation of adenosine production, by increased5′-NU activity and decreased ADA activity. Stimulation of adenosine accumulation could be of importance in mediating arginine antiatherosclerotic, vasoactive, immunomodulatory, and antioxidant effects. Assuming that the XO activity reflects the rate of purine catabolism in the cell, while the activity of AMP deaminase is of importance in ATP regeneration, reduced activity of XO, together with the increased AMP-deaminase activity, may suggest that adenine nucleotides are presumably directed to the ATP regenerating process during dietary L-arginine intake.

scholarly journals The effects of calcium ions and adenine nucleotides on the activity of pig heart 2-oxoglutarate dehydrogenase complex

1979 ◽  
Vol 180 (3) ◽  
pp. 533-544 ◽  
Author(s):  
J G McCormack ◽  
R M Denton
Keyword(s):  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Product Inhibition ◽  
Maximal Velocity ◽  
Brown Adipose ◽  
Dehydrogenase System ◽  
Oxoglutarate Dehydrogenase ◽  
Ph Range ◽  
Fold Activation ◽  
Dehydrogenase Complex

1. The effects of Ca2+ (mainly by using EGTA buffers), pH, ATP and ADP on the activity of the 2-oxoglutarate dehydrogenase complex from pig heart were explored. 2. Ca2+ (about 30 micrometer) resulted in a decrease in the apparent Km for 2-oxoglutarate from 2.1 to 0.16 mM (at pH 7) without altering the maximal velocity. At 0.1 mM-oxoglutarate there was a 4–5-fold activation by Ca2+, with an apparent Km for Ca2+ of 1.2 micrometer. A similar activation was also observed with Sr2+ (Km 15.1 micrometer), but not wised markedly from pH 7.4 TO 6.6. The effects of Ca2+ remained evident over this pH range. 4. In the presence of Mg2+, ATP resulted in a marked increase in the apparent Km for oxoglutarate, whereas ADP greatly decreased thisp arameter. The concentrations of adenine nucleotide required for half-maximal effects were about 10 micrometer in each case. 5. The effects of the adenine nucleotides and Ca2+ on the apparent Km for oxoglutarate appeared to be essentially independent of each other, reversible, and demonstrable in the presence of end product inhibition by NADH and obtained. 6. Effects similar to those described above were also observed on the activity of 2-oxoglutarate dehydrogenase from rat heart and brown adipose tissue. 7. We discuss the mechanisms controlling this enzyme's activity and compare these regulatory features with those of NAD-isocitrate dehydrogenase and the pyruvate dehydrogenase system, which are also sensitive to Ca2+ and adenine nucleotides.

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.

Adenosine metabolism in human skin fibroblasts

1985 ◽  
Vol 248 (1) ◽  
pp. C21-C26 ◽  
Author(s):  
M. J. Holland ◽  
E. Murphy ◽  
J. K. Kelleher
Keyword(s):  
Initial Rate ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Product Formation ◽  
Human Skin Fibroblasts ◽  
Metabolic Fate ◽  
Normal Cells ◽  
Extracellular Adenosine ◽  
Adenosine Concentration ◽  
The Media

When normal fibroblasts were incubated in media containing various initial concentrations of [8-14C]adenosine, ranging from 0.25 to 400 microM, under conditions where product formation was linear, greater than 90% of the intracellular label was found in adenine nucleotides, largely in the form of ATP, less than 1% of the intracellular label appeared in the nucleic acids, the remaining intracellular label was found in adenosine, inosine, and hypoxanthine, and the media contained two labeled products, inosine and hypoxanthine. Production of labeled inosine and hypoxanthine from adenosine was considerably lower in adenosine deaminase (ADA)-deficient cells than in normal cells and virtually eliminated in normal cells by the presence of 1 microM deoxycoformycin (a potent ADA inhibitor), suggesting that labeled inosine and hypoxanthine production requires ADA activity. Initial rates of deamination (inosine and hypoxanthine formation) and phosphorylation (adenine nucleotide formation) were estimated by examining the metabolic fate of [8-14C]adenosine in hypoxanthine phosphoribosyltransferase-deficient cells, which cannot recycle hypoxanthine. The estimate of the initial rate of phosphorylation exceeded that of deamination only at the lowest adenosine concentration examined (0.25 microM). The ratio of deamination to phosphorylation rose from approximately 1 at 0.41 microM to approximately 15 at 400 microM extracellular adenosine.

scholarly journals Control of adenine nucleotide metabolism in hepatic mitochondria from rats with ethanol-induced fatty liver

1982 ◽  
Vol 202 (2) ◽  
pp. 445-452 ◽  
Author(s):  
Priscilla I. Spach ◽  
Ralph E. Bottenus ◽  
Carol C. Cunningham
Keyword(s):  
Fatty Liver ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Respiratory Control ◽  
Atp Synthesis ◽  
Liver Mitochondria ◽  
Nucleotide Metabolism ◽  
Male Rats ◽  
Chain Acyl ◽  
Ethanol Feeding

Male rats developed fatty liver after being fed on an ethanol-containing diet for 31 days. Liver mitochondria from these animals catalysed ATP synthesis at a slower rate when compared with mitochondria from pair-fed control rats (control mitochondria), and demonstrated lowered respiratory control with succinate as substrate, owing to a decrease in the State-3 respiratory rate. Respiration in the presence of uncoupler was comparable in mitochondria from both groups of rats. Translocation of both ATP and ADP was decreased in mitochondria from ethanol-fed rats, with ADP uptake being lowered more dramatically by ethanol feeding. Parameters influencing adenine nucleotide translocation were investigated in mitochondria from ethanol-fed rats. Experiments performed suggested that lowered adenine nucleotide translocation in these mitochondria is not the result of inhibition of the translocase by either long-chain acyl-CoA derivatives or unesterified fatty acids. Analysis of endogenous adenine nucleotides in these mitochondria revealed lowered ATP concentrations, but no decrease in total adenine nucleotides. In experiments where the endogenous ATP in these mitochondria was shifted to higher concentrations by incubation with oxidizable substrates or defatted bovine serum albumin, the rate of ADP translocation was increased, with a linear correlation being observed between endogenous ATP concentrations and the rate of ADP translocation. The depressed ATP concentration in mitochondria from ethanol-fed rats suggests that the ATP synthetase complex is replenishing endogenous ATP at a slower rate. The lowered ATPase activity of the ATP synthetase observed in submitochondrial particles from ethanol-fed animals suggests a decrease in the function of the synthetase complex. A decrease in the rate of ATP synthesis in mitochondria from ethanol-fed rats is sufficient to explain the decreased ADP translocation and State-3 respiration.

scholarly journals The Effect of Cold on Platelets. III. Adenine Nucleotide Metabolism After Brief Storage at Cold Temperature

Blood ◽  
1973 ◽  
Vol 42 (4) ◽  
pp. 557-564 ◽  
Author(s):  
Herman E. Kattlove ◽  
Dorothy Mormino
Keyword(s):  
Connective Tissue ◽  
Prostaglandin E1 ◽  
Room Temperature ◽  
Adenine Nucleotide ◽  
Platelet Rich Plasma ◽  
Adenine Nucleotides ◽  
Nucleotide Metabolism ◽  
Immunoglobulin M ◽  
Release Reaction ◽  
Adenine Nucleotide Metabolism

Abstract The effect of cold on platelet adenine nucleotide (PAN) metabolism was studied. Spontaneous aggregation which occurs when chilled platelet-rich plasma (PRP) is simultaneously warmed and stirred was not accompanied by the changes in adenine nucleotides associated with the release reaction. Connective tissue caused the release of the same amount of ADP and conversion of equal amounts of ATP to IMP and hypoxanthine in cold-stored platelets as it did in room temperature stored platelets. However, cold did have an important effect on PAN. In PRP stored at cold (0° C, 3° C) temperatures and warmed up to 37° C in the presence of 3H adenine, there was an increase in the conversion of adenine to its metabolites and ultimately to hypoxanthine as compared to PRP stored at warmer temperatures. This effect could not be prevented by ouabain, prostaglandin E1, antibody to immunoglobulin M or adenosine.

scholarly journals Effect of adenosine on the adenine nucleotide content and metabolism of hepatocytes

1975 ◽  
Vol 152 (3) ◽  
pp. 593-599 ◽  
Author(s):  
P Lund ◽  
N W Cornell ◽  
H A Krebs
Keyword(s):  
Time Course ◽  
Ketone Bodies ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Adenosine Kinase ◽  
Urea Synthesis ◽  
O2 Consumption ◽  
Nucleotide Content ◽  
Adenosine Concentration ◽  
Glucose Formation

ADENOSINE (0.5 MM) added to hepatocyte suspensions increased the intracellular concentration of ATP and total adenine nucleotides within 60 min up to three-fold. 2. Adenosine at 0.5 mM inhibited gluconeogenesis from lactate by about 50%. At higher adenosine concentrations the inhibition was less. There was no strict parallelism between the time-course of the increase of the adenine nucleotide content and the time-course of the inhibition of gluconeogenesis from lactate. 3. Adenosine abolished the accelerating effects of oleate and dibutyryl cyclic AMP on gluconeogenesis from lactate. 4. Gluconeogenesis was no significant effect of adenosine with fructose, dihydroxyacetone or glycerol. With asparagine, adenosine caused anacceleration of glucose formation. 5. Adenosine incorporation into adenine nucleotides accounted for about 20% of the adenosine removal. 6. Inosine, hypoxanthine or adenine compared with adenosine gave relatively slight increases of adenine nucleotides. 7. Urea synthesis from NH4Cl under optimum conditions i.e. in the presence of ornithine, lactate and oleate, was also inhibited by adenosine. The inhibition increased with the adenosine concentration and was 65% at 4 mM-adenosine. Again there was no correlation between the degree of inhibition of urea synthesis and the increase in the adenine nucleotide content. 8. The basal O2 consumption, the increased O2 consumption on the addition of oleate and the rate of formation of ketone bodies were not affected by the addition of adenosine. The [β-hydroxybutyrate]/[acetoacetate] ratio was increased by adenosine, provided that lactate was present. 9. The increase of the adenine nucleotide content of the hepatocytes on the addition of adenosine may be explained on the assumption that adenosine kinase is not regulated by feedback but by substrate supply.

Increases of cell ATP produced by exogenous adenine nucleotides in isolated rabbit kidney tubules

1986 ◽  
Vol 250 (4) ◽  
pp. F720-F733 ◽  
Author(s):  
J. M. Weinberg ◽  
H. D. Humes
Keyword(s):  
Cell Injury ◽  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Recovery Period ◽  
Nucleotide Metabolism ◽  
Rabbit Kidney ◽  
Kidney Tubules ◽  
Atp Levels ◽  
Adenine Nucleotide Metabolism ◽  
Functional Consequences

The effects of exogenous nucleotides on adenine nucleotide metabolism and cell cation levels in normal and O2-deprived isolated rabbit kidney tubules were studied to gain insight into ways in which exogenous nucleotides could contribute to ameliorating O2 deprivation-induced injury. In control oxygenated tubules, 250 microM exogenous ATP, ADP, or AMP resulted in two- to threefold increases of cell ATP over 75-90 min of incubation and smaller relative increases of ADP and AMP. GTP was not increased. Exogenous adenosine, inosine, and hypoxanthine were substantially less effective at increasing intracellular nucleotides than equimolar concentrations of exogenous nucleotides. Nucleotide-treated cells had higher levels of Ca2+ and Mg2+ than untreated cells. Treatment of O2-deprived tubules with exogenous Mg-ATP improved recovery of ATP levels following O2 deprivation, and tubules with mild injury increased their ATP levels to supranormal values such as those seen in control oxygenated tubules treated with nucleotides. Increases of tubule cell ATP levels required ongoing oxidative metabolism and thus were not evident until the reoxygenation recovery period. Exogenous ATP produced some improvement of other injury-associated metabolic parameters but did not substantially alter the overall pattern of tubule susceptibility to lethal cell injury. Allopurinol did not affect the behavior of oxygenated or O2-deprived tubules irrespective of the presence of exogenous ATP. These data clarify the potential for manipulating intracellular ATP levels with exogenous nucleotides and the functional consequences of such manipulation in oxygenated and O2-deprived renal tubule cells.

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