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

Abstract

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.

Targeted Disruption of cd73 /Ecto-5′-Nucleotidase Alters Thromboregulation and Augments Vascular Inflammatory Response

“…The same result was obtained for the aorta and the femoral artery and vein (data not shown). As has been described earlier, 24 Ϫ/Ϫ mice in the presence of levamisole. Intensified staining using the azo dye method and alkaline pH (8.7) revealed that only part of the myocardial capillaries expresses AP.…”

Metabolic flux rates of adenosine in the heart

“…It was found that significant animal species differences exist with respect to the cellular localization of the enzyme (Borgers and Thone 1992). Pericytes as well as fibroblasts have been reported to stain particularly positive for ecto-5′-nucleotidase (Borgers and Thone 1992;Mlodzik et al 1995). Results on endothelial cells show a high degree of variability.…”

“…Results on endothelial cells show a high degree of variability. Ecto-5′-nucleotidase was localized on endothelial cells from resistance arterioles, while for capillary endothelial cells only a weak immunoreaction was reported (Werner and Schunke 1989;Borgers and Thone 1992;Mlodzik et al 1995). On endothelial cells from lymph vessels, however, rich enzymatic activity has been documented (Werner and Schunke 1989;Kato 1990).…”

Extracellular metabolism of ATP and other nucleotides

“…For example, in the mature brain it is mainly associated with astroglia and only exceptionally with nerve terminals (Zimmermann et al 1993). In the rat heart the enzyme was immunodetected at interstitial cells identified as pericytes or fibroblasts but not at cardiomyocytes (Mlodzik et al 1995). All these data suggest that careful biochemical analyses are required to define the enzyme species participating in extracellular nucleotide metabolism at the surface of a given cell or within defined tissue compartments.…”