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 (Emax = 125% for UTPγS, 126% for ATPγS, and 68% for αβ-MeATP), suggesting a primary role for contractile P2Y2/4 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.
Footnotes
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Send reprint requests to: Dr. Malin Malmsjö, Division of Vascular Research, Wallenberg Neuroscience Centre, Lund University Hospital, SE-221 85 Lund, Sweden. E-mail:malin.malmsjo{at}med.lu.se
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↵1 This work was supported by the Swedish Heart and Lung Foundation, the Swedish Hypertension Society, the Royal Physiographic Society (Lund), the Jeanson Foundation, the Tore Nilsson Foundation, the Svensson Siblings Foundation, and Swedish Medical Research Council Grants 13130 (to D.E.) and 5958 (to L.E.).
- Abbreviations:
- αβ-MeATP
- αβ-methylene-adenosine triphosphate
- ADPβS
- adenosine 5′-O-thiodiphosphate
- Ap4A
- diadenosine tetraphosphate
- ATPγS
- adenosine 5′-O-3-thiotriphosphate
- UDPβS
- uridine 5′-O-thiodiphosphate
- UTPγS
- uridine 5′-O-3-thiotriphosphate
- RT-PCR
- reverse transcription-polymerase chain reaction
- bp
- base pair(s)
- Received November 29, 1999.
- Accepted February 23, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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