Purine‐ and pyrimidine‐induced responses and P2Y receptor characterization in the hamster proximal urethra

1 Purine and pyrimidine compounds were investigated on hamster proximal urethral circular smooth muscle preparations. In situ hybridization studies were carried out to localize P2Y 1 , P2Y 2 , P2Y 4 and P2Y 6 mRNA. Protein expression was studied using Western blotting analysis with antibodies against P2Y 1 and P2Y 2 receptors. 2 The hamster urethra relaxed with an agonist potency order of: 2‐MeSADP> β , γ ‐meATP=ATP=adenosine=ADP>2‐MeSATP> α , β ‐meATP>TTP>CTP=UTP>GTP=UDP. The high potency of 2‐MeSADP is suggestive of an action via P2Y 1 receptors. Although the order is not characteristic for any known single P2Y receptor subtype, it may represent a combination of P2Y receptor subtypes. 3 The selective P2Y 1 receptor antagonist MRS2179 inhibited ATP‐, 2‐MeSADP‐, 2‐MeSATP‐, β , γ ‐meATP‐, and to a lesser degree α , β ‐meATP‐induced responses. 4 Adenosine, but not ATP, was inhibited by the adenosine receptor antagonist 8‐phenyltheophylline, indicating that ATP was not acting via adenosine following enzymatic breakdown. 5 Western blotting analysis showed the expression of both P2Y 1 and P2Y 2 receptors, confirming the results obtained with in situ hybridization that showed the expression of both P2Y 1 and P2Y 2 , but not P2Y 4 or P2Y 6 mRNA, in smooth muscle layers of the hamster proximal urethra. 6 It is proposed that the relaxant response of the urethra to ATP may be evoked through the activation of the combination of receptors for P2Y 1 and to a lesser extent P2Y 2 receptors, which may mediate a trophic effect in addition. A P2Y subtype responsive to α , β ‐meATP and P1 receptors may contribute to urethral smooth muscle relaxation.British Journal of Pharmacology (2005) 144 , 510–518. doi: 10.1038/sj.bjp.0706047