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Dependence of P2‐nucleotide receptor agonist‐mediated endothelium‐independent relaxation on ectonucleotidase activity and A 2A ‐receptors in rat portal vein
Author(s) -
Guibert Christelle,
Loirand Gervaise,
Vigne Paul,
Savineau JeanPierre,
Pacaud Pierre
Publication year - 1998
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0701773
Subject(s) - adenosine , agonist , biology , medicine , endocrinology , ppads , biophysics , receptor , adenine nucleotide , purinergic receptor , biochemistry , nucleotide , gene
The mechanism of action of P2 nucleotide receptor agonists that produce endothelium‐independent relaxation and the influence of ecto‐ATPase activity on this relaxing effect have been investigated in rat portal vein smooth muscle. At 25°C, ATP, 2‐methylthioATP (2‐MeSATP) and 2‐chloroATP (2‐ClATP), dose‐dependently inhibited spontaneous contractile activity of endothelium‐denuded muscular strips from rat portal vein. The rank order of agonist potency defined from the half‐inhibitory concentrations was 2‐ClATP (2.7±0.5 μ M , n =7)>ATP (12.9±1.1 μ M , n =9)2‐MeSATP (21.9±4.8 μ M , n =4). In the presence of αβ‐methylene ATP (αβ‐MeATP, 200 μ M ) which itself produced a transient contractile effect, the relaxing action of ATP and 2‐MeSATP was completely abolished and that of 2‐ClATP strongly inhibited. The non‐selective P2‐receptor antagonist pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS, 100 μ M ) did not affect the relaxation induced by ATP, 2‐MeSATP, and 2‐ClATP. The A 2A ‐adenosine receptor antagonist ZM 241385 inhibited the ATP‐induced relaxation in a concentration‐dependent manner (1–100 n M ). In the presence of 100 n M ZM 241385, the relaxing effects of 2‐MeSATP and 2‐ClATP were also inhibited. ADP, AMP and adenosine also produced concentration‐dependent inhibition of spontaneous contractions. The relaxing effects of AMP and adenosine were insensitive to αβ‐MeATP (200 μ M ) but were inhibited by ZM 241385 (100 n M ). Simultaneous measurements of contraction and ecto‐ATPase activity estimated by the degradation of [γ‐ 32 P]‐ATP showed that muscular strips rapidly (10–60 s) hydrolyzed ATP. This ecto‐ATPase activity was abolished in the presence of EDTA and was inhibited by 57±11% ( n =3) by 200 μ M αβ‐MeATP. These results suggest that ATP and other P2‐receptor agonists are relaxant in rat portal vein smooth muscle, because ectonucleotidase activity leads to the formation of adenosine which activates A 2A ‐receptors.British Journal of Pharmacology (1998) 123 , 1732–1740; doi: 10.1038/sj.bjp.0701773