The hydrolysis of extracellular adenine nucleotides by cultured endothelial cells from pig aorta. Feed-forward inhibition of adenosine production at the cell surface.

Quiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

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“…2). These kinetic determinations were in concordance with those stated for the pEC ecto-enzyme as determined by another methodology (39).…”

Section: Quiescent Aortic Endothelial Cells (Pec and Hec) Exert An Inhibitory Effect On Human Platelet Aggregation Responses Insupporting

confidence: 89%

Loss of ATP Diphosphohydrolase Activity with Endothelial Cell Activation

Robson

Kaczmarek

Siegel

et al. 1997

The Journal of Experimental Medicine

271

232

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“…The rapid initial rate of catabolism was still observed in these conditions and this lead to an apparent K M value of extracellular catabolism between 400-1200 M, considerably higher than what is found in most systems (reviewed in 40). High K M values of extracellular ATP catabolism were also found in rat ventricular myocytes, in pig arterial smooth muscle cells and in pig aorta endothelial cells and were justified by the hypothesis that the depletion of substrate at the cell surface is rate limiting for hydrolysis of ATP supplied from the bulk phase (41)(42)(43). Interestingly, ecto-ATPase was found to be located in caveolae (44), supporting the possible occurrence of channelling processes.…”

Section: Resultsmentioning

confidence: 83%

“…One issue that can only marginally be addressed with this type of studies is on the molecular entity responsible for the extracellular catabolism of ATP. Some authors favour the view that there are two main different entities, an ecto-ATPase and an ecto-ADPase (24,(41)(42)(43) whereas others champion the idea that the extracellular catabolism of ATP and ADP are mainly due to an ecto-ATP diphosphohydrolase (45)(46)(47). The observed accumulation of ADP upon ATP catabolism (Fig.…”

Section: Resultsmentioning

confidence: 99%

Untitled

Cunha

2001

Neurochemical Research

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Ecto-nucleotidases play a pivotal role in terminating the signalling via ATP and in producing adenosine, a neuromodulator in the nervous system. We have now investigated the pattern of adenosine formation with different concentrations of extracellular ATP in rat hippocampal nerve terminals. It was found that adenosine formation is delayed with increasing concentrations of ATP. Also, the rate of adenosine formation increased sharply when the extracellular concentrations of ATP + ADP decrease below 5 microM, indicating that ATP/ADP feed-forwardly inhibit ecto-5'-nucleotidase allowing a burst-like formation of adenosine possibly designed to activate facilitatory A2A receptors. Initial rate measurements of ecto-5'-nucleotidase in hippocampal nerve terminals, using IMP as substrate, showed that ATP and ADP are competitive inhibitors (apparent Ki of 14 and 4 microM). In contrast, in hippocampal immunopurified cholinergic nerve terminals, a burst-like formation of adenosine is not apparent, suggesting that channelling processes may overcome the feed-forward inhibition of ecto-5'-nucleotidase, thus favouring A1 receptor activation.

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“…Platelets release adenine nucleotides and adenosine (42). Platelet-derived ATP and ADP concentrations may reach 20 M in serum and even higher (i.e., mM) at the endothelial cell surface (43). Through endothelial cell surface conversion of ATP and ADP to 5Ј-AMP via ecto-ATP diphosphohydrolase (CD39; reference 44) and subsequent conversion to adenosine via 5Ј-ectonucleotidase/ CD73, such platelet-derived ATP and ADP may indirectly modulate endothelial paracellular permeability (44).…”

Section: Discussionmentioning

confidence: 99%

Neutrophil-derived 5′-Adenosine Monophosphate Promotes Endothelial Barrier Function via CD73-mediated Conversion to Adenosine and Endothelial A2B Receptor Activation

Lennon

Taylor

Stahl

et al. 1998

The Journal of Experimental Medicine

205

238

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During episodes of inflammation, polymorphonuclear leukocyte (PMN) transendothelial migration has the potential to disturb vascular barrier function and give rise to intravascular fluid extravasation and edema. However, little is known regarding innate mechanisms that dampen fluid loss during PMN-endothelial interactions. Using an in vitro endothelial paracellular permeability model, we observed a PMN-mediated decrease in endothelial paracellular permeability. A similar decrease was elicited by cell-free supernatants from activated PMN (FMLP 10−6 M), suggesting the presence of a PMN-derived soluble mediator(s). Biophysical and biochemical analysis of PMN supernatants revealed a role for PMN-derived 5′-adenosine monophosphate (AMP) and its metabolite, adenosine, in modulation of endothelial paracellular permeability. Supernatants from activated PMN contained micromolar concentrations of bioactive 5′-AMP and adenosine. Furthermore, exposure of endothelial monolayers to authentic 5′-AMP and adenosine increased endothelial barrier function more than twofold in both human umbilical vein endothelial cells and human microvascular endothelial cells. 5′-AMP bioactivity required endothelial CD73-mediated conversion of 5′-AMP to adenosine via its 5′-ectonucleotidase activity. Decreased endothelial paracellular permeability occurred through adenosine A2B receptor activation and was accompanied by a parallel increase in intracellular cAMP. We conclude that activated PMN release soluble mediators, such as 5′-AMP and adenosine, that promote endothelial barrier function. During inflammation, this pathway may limit potentially deleterious increases in endothelial paracellular permeability and could serve as a basic mechanism of endothelial resealing during PMN transendothelial migration.

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The hydrolysis of extracellular adenine nucleotides by cultured endothelial cells from pig aorta. Feed-forward inhibition of adenosine production at the cell surface.

Cited by 166 publications

References 43 publications

Loss of ATP Diphosphohydrolase Activity with Endothelial Cell Activation

Loss of ATP Diphosphohydrolase Activity with Endothelial Cell Activation

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Neutrophil-derived 5′-Adenosine Monophosphate Promotes Endothelial Barrier Function via CD73-mediated Conversion to Adenosine and Endothelial A2B Receptor Activation

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