Soluble forms of 5'-nucleotidase in rat and human heart

Składanowski, Andrzej C.; Smolenski, Ryszard T.; Tavenier, Monique; Jong, Jan Willem de; Yacoub, Magdi H.; Seymour, A.-M.

doi:10.1152/ajpheart.1996.270.4.h1493

Cited by 20 publications

(24 citation statements)

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“…The failure of cN-I to catalyze IMP breakdown is consistent with its preference for AMP in vitro. The kinetic properties of the enzymes from pigeon, rabbit, rat, and human are remarkably similar (15,16,32). It is therefore unlikely that our results arise from the use of a pigeon enzyme in mammalian cells.…”

Section: Atp Catabolism and Adenosine Formation In H9c2 Cells Overexpmentioning

confidence: 72%

Distinct Roles for Recombinant Cytosolic 5′-Nucleotidase-I and -II in AMP and IMP Catabolism in COS-7 and H9c2 Rat Myoblast Cell Lines

Sala-Newby¹,

Freeman²,

Składanowski³

et al. 2000

Journal of Biological Chemistry

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Catabolism of AMP during ATP breakdown produces adenosine, which restores energy balance. Catabolism of IMP may be a key step regulating purine nucleotide pools. Two, cloned cytosolic 5-nucleotidases (cN-I and cN-II) have been implicated in AMP and IMP breakdown. To evaluate their roles directly, we expressed recombinant pigeon cN-I or human cN-II at similar activities in COS-7 or H9c2 cells. During rapid (more than 90% in 10 min) or slower (30 -40% in 10 min) ATP catabolism, cN-I-transfected COS-7 and H9c2 cells produced significantly more adenosine than cN-II-transfected cells, which were similar to control-transfected cells. Inosine and hypoxanthine concentrations increased only during slower ATP catabolism. In COS-7 cells, 5-nucleotidase activity was not rate-limiting for inosine and hypoxanthine production, which was therefore unaffected by cN-II-and actually reduced by cN-I-overexpression. In H9c2 cells, in which 5-nucleotidase activity was rate-limiting, only cN-II overexpression accelerated inosine and hypoxanthine formation. Guanosine formation from GMP was also increased by cN-II. Our results imply distinct roles for cN-I and cN-II. Under the conditions tested in these cells, only cN-I plays a significant role in AMP breakdown to adenosine, whereas only cN-II breaks down IMP to inosine and GMP to guanosine.ATP levels are a key determinant of cellular function. Formation of adenosine from AMP represents an important regulatory mechanism in cellular ATP homeostasis. In the heart, for example, adenosine causes coronary vasodilatation (1), inhibits sinoatrial and atrioventricular conduction (2), antagonises production (3) and action of catecholamines (4), causes pain (5), and contributes to ischemic preconditioning (6). We proposed that adenosine acts as a "retaliatory metabolite," being formed when there is an excess of ATP breakdown over its formation and mediating the spectrum of actions designed to restore energy balance (7,8).The pathways of ATP catabolism and adenosine formation are described in Fig. 1. The nature of the enzyme responsible for cytosolic AMP catabolism to adenosine has been the subject of much controversy. Two forms of cytosolic 5Ј-nucleotidase (cN-I and cN-II) 1 (EC 3.1.3.5) have been implicated. The cN-I was very recently cloned and shown to catalyze adenosine formation during ATP breakdown (9). The role of cN-II is less clear. Levels of expression of cN-II are usually higher in cultured cells compared with the corresponding tissue. It has therefore been suggested that cN-II is particularly important in cells with high DNA synthesis or turnover (10). The cN-II was cloned from chicken, human, and ox (11, 12) and was later shown to have activity in vitro (12, 13). Stable cell lines overexpressing cN-II were recently shown to have slightly reduced total nucleoside triphosphate pools (14). However, the function of cN-II in cells undergoing ATP breakdown has remained untested.From enzyme kinetic data, the cN-I displays a preference for AMP over IMP and is stimulated by ADP but not ATP (1...

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Section: Atp Catabolism and Adenosine Formation In H9c2 Cells Overexpmentioning

confidence: 72%

Distinct Roles for Recombinant Cytosolic 5′-Nucleotidase-I and -II in AMP and IMP Catabolism in COS-7 and H9c2 Rat Myoblast Cell Lines

Sala-Newby¹,

Freeman²,

Składanowski³

et al. 2000

Journal of Biological Chemistry

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“…However, some quantitative differences may exist between species. While rat cardiomyocytes contain similar activities of N-I and N-II, human myocardium exhibits an approximately 60% higher activity of N-II as compared with N-I (Skladanowski et al 1996).…”

Section: Estimates Of the Different Sources Of Adenosinementioning

confidence: 91%

Metabolic flux rates of adenosine in the heart

Deußen

2000

Naunyn-Schmied Arch Pharmacol

101

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The quantitatively most important source of adenosine under well-oxygenated conditions is 5'-AMP hydrolyzed by cytosolic 5'-nucleotidase N-I. Hydrolysis of S-adenosylhomocysteine and extracellular dephosphorylation of 5'-AMP further contribute to total production. More than 90% of the total production occur intracellularly under well-oxygenated conditions. Besides cardiomyocytes, endothelial cells and smooth muscle contribute significantly to total cardiac adenosine production. Rapid enzymatic conversion of adenosine is provided by adenosine kinase and adenosine deaminase, keeping the cytosolic adenosine concentration in the nanomolar range. Due to the high intracellular rates of adenosine rephosphorylation and deamination the cytosolic is normally below the extracellular adenosine concentration, making the cytosol to a sink rather than a source of adenosine. It is for this reason that blockers of membrane transport enhance the plasma adenosine concentration. With increasing catabolism of adenine nucleotides the rate of intracellular adenosine production exceeds the rate of adenosine deamination and rephosphorylation. Thus, this condition will result in a concentration gradient from intra- to extracellular. Thence, membrane transport blockers would be expected to increase the intracellular adenosine concentration. A considerable insecurity on the importance of experimental data results from species differences of purine metabolism. Cardiac adenosine metabolism has recently been described in quantitative terms using mathematical model analysis. This analysis tool may prove useful in future when (1) clarifying the importance of various regulatory actions described for the different pathways of adenosine metabolism, (2) making quantitative comparisons of different experimental models possible and (3) deepening the insight from experimental data.

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“…Nevertheless, a study of the activity of 5Ј-nucleotidase in the human heart failed to detect differences between these 2 sites. 32 Second, ecto-5Ј-nucleotidase activity was determined only at baseline and at the completion of the preconditioning protocol. A subsequent measurement during the period of aortic cross-clamping was not possible because of the limited amount of right atrial tissue available for sampling; consequently, the time course of ecto-5Ј-nucleotidase activity throughout the operation cannot be conclusively established.…”

Section: Ii-342mentioning

confidence: 99%

Evidence for Preconditioning by Isoflurane in Coronary Artery Bypass Graft Surgery

Belhomme¹,

Peynet²,

Louzy³

et al. 1999

Circulation

207

106

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Background-Experimentally, isoflurane, a commonly used volatile anesthetic agent, mimics the cardioprotective effects of ischemic preconditioning via a mechanism that could involve the activation of protein kinase C. The present study was designed to assess the clinical relevance of this observation in patients undergoing elective CABG. Methods and Results-Twenty patients were included in the study. In 10 of them, preconditioning was elicited after the onset of cardiopulmonary bypass via a 5-minute exposure to isoflurane (2.5 minimum alveolar concentration), followed by a 10-minute washout before aortic cross-clamping and cardioplegic arrest. Ten case-matched control patients underwent an equivalent period (15 minutes) of prearrest isoflurane-free bypass. Outcome measurements included troponin I and creatine kinase-MB isoenzyme (until the third postoperative day) levels and the activity of ecto-5Ј-nucleotidase, which contributes to adenosine production and is considered to be a reporter of protein kinase C activation, as assessed in right atrial biopsy samples taken before bypass and at the end of the preconditioning protocol (or after 15 minutes of bypass in control patients Key Words: ischemia Ⅲ bypass Ⅲ anesthesia I schemic preconditioning is recognized as one of the most effective means of reducing cellular necrosis. As such, its implementation during cardiac surgery might be clinically relevant, particularly in high-risk patients in whom any additional myocardial ischemic injury induced with cardiopulmonary bypass and superimposed cardioplegic arrest can adversely affect postoperative outcome. Because in this setting it is particularly desirable to avoid an ischemic-type preconditioning stimulus, 1-3 extensive research is targeted toward identifying the pharmacological mediators of the preconditioning phenomenon in an attempt to exploit them therapeutically.There is compelling evidence that the preconditioning signal activates various membrane receptors, which triggers a signaling pathway leading to the activation of several kinases, 4 in particular, protein kinase C (PKC), 5 and the subsequent opening of ATP-dependent potassium channels, possibly at the mitochondrial level. 6,7 How opening of these channels elicits cardioprotection is not yet established but might involve the limitation of calcium influx, better control of cellular volume, or both. This scheme provides a framework for rationalizing interventions targeted at mimicking preconditioning and, in this perspective, makes logical the use, among other drugs, of potassium channel openers.Within this class of drugs, only nicorandil is currently available for human use. However, aside from the fact that nicorandil cannot be administered intravenously, this compound has marked nitrovasodilatory properties, which can be Circulation is available at http://www.circulationaha.org II-340by guest on May 10, 2018http://circ.ahajournals.org/ Downloaded from of concern. Alternatively, isoflurane is a volatile anesthetic agent that has been reported in animal mo...

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Soluble forms of 5'-nucleotidase in rat and human heart

Cited by 20 publications

References 0 publications

Distinct Roles for Recombinant Cytosolic 5′-Nucleotidase-I and -II in AMP and IMP Catabolism in COS-7 and H9c2 Rat Myoblast Cell Lines

Distinct Roles for Recombinant Cytosolic 5′-Nucleotidase-I and -II in AMP and IMP Catabolism in COS-7 and H9c2 Rat Myoblast Cell Lines

Metabolic flux rates of adenosine in the heart

Evidence for Preconditioning by Isoflurane in Coronary Artery Bypass Graft Surgery

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