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Membrane-bound and releasable nucleotidase activities: Differences in canine mesenteric artery and vein

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1. At least two enzymatic activities are proposed to degrade the extracellular ATP: (i) ubiquitously expressed membrane-bound enzymes (ecto-nucleotidases); and (ii) soluble (releasable) nucleotidases that are released during stimulation of sympathetic nerves and break down neuronal ATP. No quantitative data have placed the magnitude of these nucleotidase activities into a physiological perspective of neurovascular control.

2. We studied comparatively the membrane-bound and releasable nucleotidase activities in canine isolated inferior mesenteric arteries and veins using 1,N6-etheno(ε)-nucleotides (i.e. ε-ATP, ε-ADP, ε-AMP and ε-adenosine) as exogenous substrates. The enzymatic activities were estimated by measuring the disappearance of the ε-substrate and appearance of ε-products by means of HPLC–fluorescence detection during either stimulation of sympathetic perivascular nerves (releasable activity) or in the absence of nerve stimulation (ecto-nucleotidase activity).

3. Incubation of vascular segments with 50 nmol/L ε-ATP for 60 min resulted in a decrease of the ε-ATP substrate by 63.5 ± 4.6 and 91.2 ± 6.2% in the artery and vein, respectively. In contrast, the decrease of the ε-ATP during electrical field stimulation (EFS; 16 Hz, 0.3 msec, 2 min) was 39.8 ± 4.2% in the artery and 13.1 ± 7.3% in the vein. Therefore, the mesenteric arteries demonstrate a greater releasable ATPase activity and a weaker ecto-ATPase activity than mesenteric veins.

4. The degradation of ε-ADP and ε-AMP was similar in both blood vessels under either experimental protocol. The ε-adenosine was not significantly degraded in the absence or presence of EFS.

5. These data implicate a differential removal of extracellular ATP as a potential mechanism of serving resistance and capacitance in the splanchnic circulation.
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Keywords: autonomic nervous system; ecto-nucleotidases; etheno-nucleotides; extracellular ATP; mesenteric artery; mesenteric vein; releasable nucleotidases

Document Type: Research Article

Affiliations: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA

Publication date: March 1, 2003

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