Characterization of contractile P2 receptors in human coronary arteries byuse of the stable pyrimidines uridine 5 '-O-thiodiphosphate and uridine 5 '-O-3-thiotriphosphate

The present study was designed to evaluate the relative contribution of the different contractile P2 receptors in endothelium-denuded human coronary a rteries by use of extracellular nucleotides, including the stable pyrimidin es uridine 5'-O-3-thiotriphosphate (UTP gamma S) and uridine 5'-O-thiodipho sphate (UDP beta S). The isometric tension of isolated vessel segments was recorded in vitro, and P2 receptor mRNA expression was examined by reverse transcription-polymerase chain reaction. alpha beta-Methylene-adenosine tri phosphate (alpha beta-MeATP) elicited contractions at a low concentration ( pEC(50) = 5.2), indicating the presence of contractile P2X receptors. The P 2Y responses were analyzed after P2X receptor desensitization with 10 mu M alpha beta-MeATP. The stable nucleotides ATP gamma S and adenosine 5'-O-3-t hiotriphosphate (ATP gamma S), which are agonists of P2Y(2) or P2Y(4) recep tors, were approximately 2 log units more potent than the endogenous UTP an d ATP (pEC(50) = 4.6 and 3.8 for UTP gamma S and ATP gamma S). The efficacy of these responses were approximately double that of the P2X agonist alpha beta-MeATP (E (max) = 125% for UTP gamma S, 126% for ATP gamma S and 68% f or alpha beta-MeATP), suggesting a primary role for contractile P2Y(2/4) re ceptors. The P2Y(2) receptor agonist diadenosine tetraphosphate also stimul ated contraction, whereas the selective P2Y(1) agonist adenosine 5'-O-thiod iphosphate and the selective P2Y(6) agonist UDP beta S had no effect. Rever se transcription-polymerase chain reaction analysis of mRNA from endotheliu m-denuded human coronary arteries demonstrated strong bands for P2Y(2) and P2X(1), although bands for P2Y(1), P2Y(4), and P2Y(6) receptor mRNA could a lso be detected. In conclusion, the stable pyrimidines UDP beta S and UTP g amma S are important tools for P2 receptor subtype characterization in inta ct tissues with ectonucleotidase activity. Extracellular nucleotides elicit contraction of human coronary arteries primarily by activation of P2Y(2) a nd P2X receptors, whereas a role for P2Y(1) and P2Y(4) receptors can be exc luded. Antagonists of P2Y(2) and P2X receptors may be useful in the treatme nt of coronary vasospastic disorders.