Abstract

ATP and UDP constrict rat intrapulmonary arteries, but which receptors mediate these actions is unclear. Here, we used selective agonists and antagonists, along with measurements of P2Y receptor expression, to characterize the receptor subtypes involved. Isometric tension was recorded from endothelium-denuded rat intrapulmonary artery rings (i.d. 200–500 μm) mounted on a wire myograph. Expression of P2Y receptor subtype expression was determined by using reverse transcription-polymerase chain reaction with receptor-specific oligonucleotide primers. The selective P2Y₁ agonist (N)-methanocarba-2-methylthioadenosine-5′-O-diphosphate (MRS2365) induced small, concentration-dependent contractions that were inhibited by the P2Y₁ antagonist N⁶-methyl-2′-deoxyadenosine-3′,5′-bisphosphate (MRS2179). Contractions evoked by ATP were unaffected by MRS2179, but inhibited by approximately one-third by the P2Y₁₂ antagonist N⁶-(2-methylthiomethyl)-2-(3,3,3-trifluoropropylthio)dichloro-methylene ATP (AR-C69931MX). Combined blockade of P2X1 and P2Y₁₂ receptors virtually abolished the response to ATP. ADP also evoked contractions that were abolished by AR-C69931MX. The selective P2Y₆ receptor agonist 3-(2-oxo-2-phenylethyl)-UDP (PSB 0474) evoked concentration-dependent contractions and was approximately three times more potent than UDP, but the P2Y₁₄ agonist UDP-glucose had no effect. Contractions evoked by UDP were inhibited by the P2Y₆ receptor antagonist N,N′-1,4-butanediylbis-N′-(3-isothiocyanatophenyl)thiourea (MRS2578), but not the cysteinyl leukotriene 1 (CysL₁) antagonist 3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl)((3-dimethylamino-3-oxopropyl)thio)methyl)thiopropanoic acid (MK571). Higher concentrations of MRS2578 inhibited contractions to KCl, so they were not studied further. mRNA for P2Y₁, P2Y₆, and P2Y₁₂ receptors was identified. Our working model is that P2Y₁₂ and P2X1 receptors are present in rat intrapulmonary arteries and together mediate ATP-induced vasoconstriction. Contractile P2Y₆, but not P2Y₁₄ or CysLT₁, receptors are also present and are a major site through which UDP evokes constriction.