Abstract

The present study was designed to evaluate the relative contribution of the different contractile P2 receptors in endothelium-denuded human coronary arteries by use of extracellular nucleotides, including the stable pyrimidines uridine 5′-O-3-thiotriphosphate (UTPγS) and uridine 5′-O-thiodiphosphate (UDPβS). The isometric tension of isolated vessel segments was recorded in vitro, and P2 receptor mRNA expression was examined by reverse transcription-polymerase chain reaction. αβ-Methylene-adenosine triphosphate (αβ-MeATP) elicited contractions at a low concentration (pEC₅₀ = 5.2), indicating the presence of contractile P2X receptors. The P2Y responses were analyzed after P2X receptor desensitization with 10 μM αβ-MeATP. The stable nucleotides UTPγS and adenosine 5′-O-3-thiotriphosphate (ATPγS), which are agonists of P2Y₂ or P2Y₄ receptors, were approximately 2 log units more potent than the endogenous UTP and ATP (pEC₅₀ = 4.6 and 3.8 for UTPγS and ATPγS). The efficacy of these responses were approximately double that of the P2X agonist αβ-MeATP (E_max = 125% for UTPγS, 126% for ATPγS, and 68% for αβ-MeATP), suggesting a primary role for contractile P2Y_2/4 receptors. The P2Y₂ receptor agonist diadenosine tetraphosphate also stimulated contraction, whereas the selective P2Y₁ agonist adenosine 5′-O-thiodiphosphate and the selective P2Y₆ agonist UDPβS had no effect. Reverse transcription-polymerase chain reaction analysis of mRNA from endothelium-denuded human coronary arteries demonstrated strong bands for P2Y₂ and P2X₁, although bands for P2Y₁, P2Y₄, and P2Y₆ receptor mRNA could also be detected. In conclusion, the stable pyrimidines UDPβS and UTPγS are important tools for P2 receptor subtype characterization in intact tissues with ectonucleotidase activity. Extracellular nucleotides elicit contraction of human coronary arteries primarily by activation of P2Y₂ and P2X receptors, whereas a role for P2Y₁ and P2Y₆ receptors can be excluded. Antagonists of P2Y₂ and P2X receptors may be useful in the treatment of coronary vasospastic disorders.