Lack of uptake, release and action of UTP at sympathetic perivascular nerve terminals in rabbit ear artery

Abstract

A possible role of uridine 5′-triphosphate (UTP) and uridine at sympathetic nerve terminals was studied in the rabbit ear artery after incubation of isolated vessels with [ 3 H ]uridine or [ 3 H ]noradrenaline. It was found that [ 3 H ]uridine was taken up by rabbit ear artery. This uptake was largely suppressed after the removal of endothelium and was inhibited by ethidium bromide and dipyridamole. Chemical denervation of the vessels with 6-hydroxydopamine did not reduce the uptake. Following pre-incubation of the isolated vessels with [ 3 H ]uridine, there was a release of radioactivity from the superfused rabbit ear artery. UTP, UDP, UMP and uridine were detected by thin layer chromatography both in the superfusate and inside the vessels. Transmural electric stimulation (30 V, 5 Hz) induced a contraction of the vessels but did not increase the release of uridine nucleotides into the superfusate. [ 3 H ]Noradrenaline was released during electric stimulation and the addition of UTP (100 μM) had no effects on this release. To conclude, this study shows that in contrast to endothelial cells, the sympathetic nerve terminals of the rabbit ear artery do not take up uridine and do not release uridine-derived nucleotides. UTP at 100 μM is also unable to modulate the evoked release of noradrenaline. These results mainly confine the role of UTP in endothelium-derived vasodilatation via P2Y 2 and/or P2Y 4 receptors.