5′-Nucleotidase activity of isolated mature rat cardiac myocytes

Bowditch, Julia; Nigdikar, Shailja; Brown, Anne K.; Dow, Jocelyn W.

doi:10.1016/0167-4889(85)90049-7

Cited by 25 publications

(8 citation statements)

References 31 publications

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“…An extracellular source of adenosine is provided by 5′-AMP degraded by action of ecto-5′-nucleotidase (Frick and Lowenstein 1978;Schutz et al 1981;Bowditch et al 1985;Dieckhoff et al 1986;Darvish et al 1996). This enzyme is bound to the cell membrane via a GPI-anchor (Panagia et al 1981), the catalytic site facing the extracellular region (Fleetwood et al 1989;Meghji et al 1992Meghji et al , 1995.…”

Section: Overview Of Adenosine Metabolismmentioning

confidence: 99%

“…In heart tissue ecto-5′-nucleotidase activity exhibits striking species differences (Meghji et al 1988b). In addition to the activities of 5′-nucleotidases, alkaline phosphatases have been associated with cytosolic and membrane fractions from cardiac muscle Bowditch et al 1985). However, although the enzyme activities of alkaline phosphatases may be in the range of those of 5′-nucleotidase activities, their contribution to adenosine production may usually be small as the K m -values of alkaline phosphatases are high.…”

Section: Overview Of Adenosine Metabolismmentioning

confidence: 99%

“…Furthermore, ecto-5′-nucleotidase has been reported on smooth muscle cells (Dieckhoff et al 1986;Nitahara et al 1995) where it may be localized with caveolae (Kittel and Bacsy 1994). On cardiomyocytes the enzyme has been documented only in rat heart (Bowditch et al 1985;Borgers and Thone 1992;Aleksiuk et al 1993) and most recently in mouse heart (Fretes et al 1999).…”

Section: Estimates Of the Different Sources Of Adenosinementioning

confidence: 99%

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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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Section: Overview Of Adenosine Metabolismmentioning

confidence: 99%

Section: Overview Of Adenosine Metabolismmentioning

confidence: 99%

Section: Estimates Of the Different Sources Of Adenosinementioning

confidence: 99%

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Metabolic flux rates of adenosine in the heart

Deußen

2000

Naunyn-Schmied Arch Pharmacol

101

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“…It has been shown that the extent of recovery of myocardial contractile function after a period of anoxia is well correlated with the size of total adenine nucleotides [35,36]. The action of AK under anaerobic conditions could result in accumulation of AMR AMP is then deaminated by AMP deaminase [37][38][39] which is bound to myofibrils [40] at both ends of the A band [41] into IMR AMP and IMP are then dephosphorylated by 5'-nucleotidase located on the sarcolemma [42] to give adenosine and inosine which can leak out of the cell and lead to the loss of the adenine nucleotide pool [43]. This became apparent when we showed that if the action of myocardial AK was reduced during the anoxic period, the nucleotide pool was preserved and a greater and more complete recovery of the contractile function was possible after reoxygenation [36].…”

Section: Adenylate Kinase and The Glycolytic Metabolism Of High Energmentioning

confidence: 99%

Interaction of creatine kinase and adenylate kinase systems in muscle cells

Savabi

1994

Mol Cell Biochem

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Elsewhere in this book the important role of creatine kinase and its metabolites in high energy phosphate metabolism and transport in muscle cells has been reviewed. The emphasis of this review article is mainly on the compartmentalized catalytic activity of adenylate kinase in relation to creatine kinase isoenzymes, and other enzymes of energy production and utilization processes in muscle cells. At present the role of adenylate kinase is considered simply to equilibrate the stores of adenine nucleotides. Recent studies by us and others, however, suggest an entirely new view of the metabolic importance of adenylate kinase in muscle function. This view offers a closer interaction between adenylate kinase and creatine kinase, in the process of energy production (at mitochondrial and glycolytic sites), and energy utilization (at myofibrillar sites and perhaps other sites such as sarcoplasmic reticular, sarcolemmal membrane, etc.), thus being an integral part of the high energy phosphate transport system. This review article opens up the opportunity to further examine the metabolism of adenine nucleotides and their fluxes through the adenylate kinase system in intact muscle cells. Using an intact system, having a preserved integrity of their compartmentalized enzymes and substrates, is essential in clarifying the exact role of adenylate kinase in high energy phosphate metabolism in muscle cells.

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“…It is metabolized by deamination to inosine by adenosine deaminase (adenosine aminohydrolase: EC 3.5.4.4), phosphorylation to AMP by adenosine kinase (ATP: adenosine 5'-phosphotransferase; EC 2.7.1.20), or by combination with homocysteine to form S-adenosyl-1-homocysteine by Sadenosyl homocysteine hydrolase (EC 3.3.1.1) and is synthesized from 5'-AMP by 5'-nucleotidase (EC 3.1.3.5) (Fox & Kelley, 1978). In many tissues, 5'-nucleotidase is an intrinsic plasma membrane enzyme with an externally directed active site, thus functioning as an ecto-enzyme (Trams & Lauter, 1974;Newby, 1980;Edwards et ., 1982;Bowditch et al, 1985), while some tissues also contain a different soluble intracellular form of the enzyme (Schutz et al, 1981). Little is known about the ability of spermatozoa to metabolize adenosine, although the classic study by Mann (1945) contrasted the poor deaminase activity of spermatozoa and semen with the powerful 'adenyl phosphatase' activity.…”

Section: Introductionmentioning

confidence: 99%

Enzymes of adenosine metabolism in mouse sperm suspensions

Monks

Fraser²

1988

Reproduction

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Summary. The enzymes of adenosine metabolism were investigated in suspensions of epididymal mouse spermatozoa incubated under conditions which support capacitation in vitro. High levels of adenosine deaminase activity were found in sperm suspensions, but the enzyme was located in the surrounding medium and was not intrinsic to spermatozoa. 5\m='\-Nucleotidase was also present in the surrounding medium while in sperm cells it existed as an ecto-enzyme. Adenosine was not metabolized by washed spermatozoa under conditions used for the assay of adenosine deaminase or adenosine kinase, but it was metabolized rapidly by unwashed sperm suspensions. Incubation of sperm suspensions in conditions which modulate fertilizing ability resulted in small alterations in intrinsic 5\m='\-nucleotidase activity of spermatozoa. In contrast, the activity of adenosine deaminase was not consistently modulated by such maniupulations.Adenosine deaminase and 5\m='\-nucleotidase exhibited similar kinetic parameters to enzymes from other sources and their activities were inhibited by coformycin and \ g = a \ , \ g = b \ \ x = r e q -\ methylene adenosine 5\m='\-diphosphate, respectively. These studies highlight the low adenosine-metabolizing ability of spermatozoa coupled with the extensive metabolism in the medium which surrounds them. Extracellular adenosine metabolism can therefore occur and may modulate capacitation in vitro.

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5′-Nucleotidase activity of isolated mature rat cardiac myocytes

Cited by 25 publications

References 31 publications

Metabolic flux rates of adenosine in the heart

Metabolic flux rates of adenosine in the heart

Interaction of creatine kinase and adenylate kinase systems in muscle cells

Enzymes of adenosine metabolism in mouse sperm suspensions

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