Production of AMP and adenosine in the interstitial fluid compartment of the isolated perfused normoxic guinea pig heart

Imai, Shoichi; Chin, Wan-Pao; Jin, Hiromasa; Nakazawa, Makoto

doi:10.1007/bf00585055

Cited by 39 publications

(13 citation statements)

References 46 publications

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“…Membrane-bound 5Ј-nucleotidase has been documented histochemically on the cell surface of cardiomyocytes and vascular cells of guinea pig heart. 16 In this species, AMP is recovered from an extracellular fluid region, 7 and coronary venous adenine nucleotide release is 40 pmol ⅐ min Ϫ1 ⅐ g Ϫ1 under control conditions and 430 pmol ⅐ min Ϫ1 ⅐ g Ϫ1 during ecto-5Ј-nucleotidase inhibition by ␣,␤-methyleneadenosine diphosphate. 8 This release is quantitatively sufficient to account for the extracellular adenosine production rate estimated in the present experiments.…”

Section: Extracellular Adenosine Productionmentioning

confidence: 96%

“…2 An explanation for this discrepancy could be that these blockers inhibit only inward membrane transport in the heart. Alternatively, enhanced vascular concentrations seem possible if net uptake of adenosine supplied by extracellular dephosphorylation of adenine nucleotides 7,8 is inhibited. A previous limitation in discerning between these alternative explanations has been the inability to measure the adenosine concentration on both sides of the membrane.…”

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confidence: 99%

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Quantification of Extracellular and Intracellular Adenosine Production

et al. 1999

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Background-Inhibitors of adenosine membrane transport cause vasodilation and enhance the plasma adenosine concentration. However, it is unclear why the plasma adenosine concentration rises rather than falls when membrane transport is inhibited. We tested the hypothesis that the cytosolic adenosine concentration exceeds the interstitial concentration under well-oxygenated conditions. Methods and Results-In isolated, isovolumically working guinea pig hearts (nϭ50), the release rate of adenosine and accumulation of S-adenosylhomocysteine (after 20 minutes of 200 mol/L homocysteine), a measure of the free cytosolic adenosine concentration, were determined in the absence and presence of specific and powerful blockers of adenosine membrane transport (nitrobenzylthioinosine 1 mol/L), adenosine deaminase (erythro-9-hydroxy-nonyladenine 5 mol/L), and adenosine kinase (iodotubericidine 10 mol/L). Data analysis with a distributed multicompartment model revealed a total cardiac adenosine production rate of 2294 pmol ⅐ min Ϫ1 ⅐ g Ϫ1 , of which 8% was produced in the extracellular region. Because of a high rate of intracellular metabolism, however, 70.3% of extracellularly produced adenosine was taken up into cellular regions, an effect that was effectively eliminated by membrane transport block. The resulting Ϸ2.8-fold increase of the interstitial adenosine concentration evoked near-maximal coronary dilation. Conclusions-We rejected the hypothesis that the cytosolic adenosine concentration exceeds the interstitial. Rather, there is significant extracellular production, and the parenchymal cell represents a sink, not a source, for adenosine under well-oxygenated conditions. (Circulation. 1999;99:2041-2047.)

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Section: Extracellular Adenosine Productionmentioning

confidence: 96%

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confidence: 99%

Quantification of Extracellular and Intracellular Adenosine Production

et al. 1999

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“…Whether nucleotides can diffuse out of the cardiomyocytes has not been demonstrated but AMP has been found in the interstitial fluid of the myocardium (Imai et al 1989;Zhu et al 1991). Nerve endings (Imai et al 1989) and capillary endothelia (Yang et aI.…”

Section: Functional Implications Of Ecto-5'-nucteotidase In Interstitmentioning

confidence: 97%

Ecto-5?-nucleotidase is expressed by pericytes and fibroblasts in the rat heart

Mlodzik

Loffing

Hir

et al. 1995

Histochem Cell Biol

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Ecto-5'-nucleotidase is anchored at the outer surface of cell membranes and thus its reaction product adenosine is released into the extracellular space. Extracellular adenosine displays via specific receptors a wide range of physiological effects in heart. There are discrepancies in the literature concerning the distribution of ecto-5'-nucleotidase in heart. Since we suspected that these may be due to technical problems, in the present study on ecto-5'-nucleotidase in rat heart we attempted to circumvent some technical pitfalls. Good preservation of the tissue with open capillary lumina, providing a clear identification of endothelium, was obtained by perfusion fixation. At the light microscopic level, the distribution of ecto-5'-nucleotidase studied by enzyme histochemistry and immunohistochemistry using a monoclonal and a polyclonal antibody yielded congruent results. The enzyme was rather homogeneously distributed throughout the myocardium, with a slightly higher incidence of stained cells in the outer thirds than in the inner third of the wall. Consistently high levels of ecto-5'-nucleotidase were seen only in interstitial cells. The walls of large vessels and heart muscle cells were constantly negative for ecto-5'-nucleotidase. The endothelia of capillaries were mostly negative but a few profiles occasionally displayed a weak immunoreaction. The interstitial cells staining positive for ecto-5'-nucleotidase could be identified as pericytes and as fibroblasts according to their shapes and localizations. The immunoreactivity of fibroblasts was confirmed by electron microscopy. These data indicate that adenosine may be formed extracellularly in the interstitium of the myocardium, where it would have direct access to important targets such as myocytes, arterioles and nerve endings.

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“…Despite earlier pioneering work on the release of adenine nucleotides from endothelial and smooth muscle cells (Pearson and Gordon 1979), blood cells (Coade and Pearson 1989;Morabito et al 1998) or isolated perfused heart (Imai et al 1989;Borst and Schrader 1991), the quantitative importance of ecto-5′-nucleotidase in contributing to native cardiac adenosine production has been successfully addressed only recently (Deussen et al 1999). From a total adenosine production of approximately 2.3 nmol min -1 g -1 only 8% could be attributed to extracellular production most likely via ecto-5′-nucleotidase in guinea pig heart during well-oxygenated conditions.…”

Section: Estimates Of the Different Sources Of Adenosinementioning

confidence: 98%

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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Production of AMP and adenosine in the interstitial fluid compartment of the isolated perfused normoxic guinea pig heart

Cited by 39 publications

References 46 publications

Quantification of Extracellular and Intracellular Adenosine Production

Quantification of Extracellular and Intracellular Adenosine Production

Ecto-5?-nucleotidase is expressed by pericytes and fibroblasts in the rat heart

Metabolic flux rates of adenosine in the heart

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