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      Adenosine Diphosphate Ribose Dilates Bovine Coronary Small Arteries through Apyrase- and 5′-Nucleotidase-Mediated Metabolism


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          Cyclic adenosine diphosphate ribose and adenosine diphosphate ribose (ADPR) play an important role in the regulation of intracellular Ca<sup>2+</sup> release and K<sup>+</sup> channel activity in the coronary arterial smooth muscle. The role of these signaling nucleotides in the control of vascular tone has yet to be determined. The present study was designed to determine whether ADPR produces vasodilation in coronary arteries and to explore the mechanism of action of ADPR. ADPR (10–60 µmol/l) was found to produce endothelium-independent relaxation in a concentration-dependent manner in isolated and pressurized small bovine coronary arteries. The ADPR-induced vasodilation was substantially attenuated by adenosine deaminase (0.2 U/ml), and the P<sub>1</sub> purinoceptor antagonist 8-( p-sulfophenyl)theophylline (50 µmol/l), with maximal inhibitions of 60 and 80%, respectively. When the coronary arterial homogenates were incubated with ADPR, the production of adenosine and 5′-AMP was detected. The adenosine production was blocked by the 5′-nucleotidase inhibitor, α,β-methylene adenosine 5′-diphosphate (MADP, 1 mmol/l), which was accompanied by a corresponding accumulation of 5′-AMP. This 5′-AMP accumulation was substantially inhibited by the apyrase inhibitor sodium azide (10 mmol/l). Moreover, ADPR was hydrolyzed into 5′-AMP by purified apyrase. In agreement with their inhibitory effect on the adenosine production, MADP and sodium azide significantly attenuated the vasodilator response to ADPR. The metabolism of ADPR to adenosine was only detected in cultured coronary arterial smooth muscle cells but not in endothelial cells. We concluded that ADPR produces vasodilation in small coronary arteries and that the action of ADPR is associated with the adenosine production via an apyrase- and 5′-nucleotidase-mediated metabolism.

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          Most cited references 11

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          Biochemistry, localization and functional roles of ecto-nucleotidases in the nervous system.

           H Zimmermann (1996)
          Nucleotides such as ATP, ADP, UTP or the diadenosine polyphosphates and possibly even NAD+ are extracellular signaling substances in the brain and in other tissues. Enzymes located on the cell surface catalyze the hydrolysis of these compounds and thus limit their spatio-temporal activity. As a final hydrolysis product they generate the nucleoside and phosphate. The paper discusses the biochemical properties, cellular localization and functional properties of surface-located enzymes that hydrolyse nucleotides released from nervous tissue. This is preceded by a brief discussion of nucleotide receptors, cellular storage and mechanisms of nucleotide release. In nervous tissue nucleoside 5'-triphosphates are hydrolysed by ecto-ATP-diphosphohydrolase and possibly in addition also by ecto-nucleoside triphosphatase and ecto-nucleoside diphosphatase. The molecular identity of the ATP-diphosphohydrolase has now been revealed. The hydrolysis of nucleoside 5'-monophosphates is catalysed by 5'-nucleotidase whose biochemical properties and molecular structure have been studied in detail. Little is known about the molecular properties of the diadenosine polyphosphatases. Surface located enzymes for the extracellular hydrolysis of NAD+ and also ecto-protein kinases are discussed briefly. The cellular localization of the ecto-nucleotidases is only partly defined. Whereas in adult mammalian brain activity for hydrolysis of ATP and ADP may be associated with nerve cells or glial cells 5'-nucleotidase appears to have a preferential glial allocation in the adult mammal. The extracellular hydrolysis of the nucleotides is of functional importance not only during synaptic transmission where it functions in signal elimination. It plays a crucial role also for the survival and differentiation of neural cells in vitro and presumably during neuronal development in vivo.
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            The protective role of adenosine in inducing nitric oxide synthesis in rat liver ischemia preconditioning is mediated by activation of adenosine A2 receptors.

             N. Prats,  D Closa,  E Gelpí (1999)
            This study aims to determine if the protective role of adenosine in liver ischemic preconditioning is mediated by the activation of adenosine receptors and to ascertain which of these receptors is implicated in the process. Administration of adenosine A1 and A2 receptor antagonists to preconditioned animals indicates that hepatic preconditioning is mediated by the activation of adenosine A2 receptors. Propentofylline (an inhibitor of adenosine transport into cells) in the preconditioned group, subjected to previous administration of an adenosine A2 receptor antagonist, prevented the negative effect of the latter on the protection offered by preconditioning. An increase of NO production was detected just immediately after hepatic preconditioning, and the administration of an adenosine A2 receptor antagonist to the preconditioning group prevented this increase, thus abolishing the protective effect of preconditioning. However, the administration of a NO donor to the preconditioned group subjected to previous administration of the adenosine A2 receptor antagonist was able to maintain the preconditioning effects. In conclusion, these results indicate that, in preconditioning, the protective effect of adenosine could be a result of an increase in extracellular adenosine. This in turn would induce the activation of adenosine A2 receptors, which, by eliciting an increase in NO generation, would protect against the injury associated with hepatic ischemia-reperfusion.
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              cGMP mobilizes intracellular Ca2+ in sea urchin eggs by stimulating cyclic ADP-ribose synthesis.

              Many hormones or neurotransmitters act at cell surface receptors to increase the intracellular free calcium concentration, triggering a wide range of cellular responses. As the source of this Ca2+ is often internal stores, additional messengers are required to convey the hormonal message from the plasma membrane. Cyclic ADP-ribose (cADPR) has been proposed as the endogenous activator of Ca(2+)-induced Ca2+ release by the ryanodine receptor in sea urchin eggs and in several mammalian cell types. A second messenger role for cADPR requires that its intracellular levels be under the control of extracellular stimuli. Here we demonstrate a novel action of 3',5'-cyclic guanosine monophosphate (cGMP) in stimulating the synthesis of cADPR from beta-NAD+ by activating its synthetic enzyme ADP-ribosyl cyclase in sea urchin eggs and egg homogenates. We suggest that cADPR may transduce signals generated by cell surface receptors or gaseous transmitters linked to cGMP production.

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                February 2001
                08 February 2001
                : 38
                : 1
                : 64-72
                Departments of Pharmacology and Toxicology and Physiology, Medical College of Wisconsin, Milwaukee, Wisc., USA
                51031 J Vasc Res 2001;38:64–72
                © 2001 S. Karger AG, Basel

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                Page count
                Figures: 7, References: 56, Pages: 9
                Research Paper


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