Membrane-bound and releasable nucleotidase activities: differences in canine mesenteric artery and vein.
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(epsilon)-nucleotides (i.e. epsilon-ATP, epsilon-ADP, epsilon-AMP and epsilon-adenosine) as exogenous substrates. The enzymatic activities were estimated by measuring the disappearance of the epsilon-substrate and appearance of epsilon-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 epsilon-ATP for 60 min resulted in a decrease of the epsilon-ATP substrate by 63.5 +/- 4.6 and 91.2 +/- 6.2% in the artery and vein, respectively. In contrast, the decrease of the epsilon-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 epsilon-ADP and epsilon-AMP was similar in both blood vessels under either experimental protocol. The epsilon-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.
Bobalova
Janette
J
Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
Mutafova-Yambolieva
Violeta N
VN
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D004285:Dogs; D004558:Electric Stimulation; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008638:Mesenteric Arteries / Q000201:enzymology* / Q000378:metabolism; D008642:Mesenteric Veins / Q000201:enzymology* / Q000378:metabolism; D009708:Nucleotidases / Q000378:metabolism*
D008565:Membrane Proteins; D009708:Nucleotidases; C030287:nucleotidase