Contractions in human coronary bypass vessels stimulated by extracellular nucleotides

Background The present study was designed to evaluate the relative contribution of different contractile P2 receptors in human saphenous vein compared with internal mammary artery obtained during coronary artery surgery. Methods The isometric tension in endothelium-denuded isolated vessel segments was recorded in vitro. The P2 receptor mRNA expression was quantified by real-time polymerase chain reaction. Results The P2X1 receptor agonist, αβ-MeATP (αβ-methylene-adenosine triphosphate), was the most potent vasoconstrictor, with more efficacious contractions in the saphenous vein than in the internal mammary artery. The selective P2Y6 receptor agonist, UDPβS (uridine 5’-O-thiodiphosphate), stimulated more potent contractions in saphenous vein compared with internal mammary artery. Furthermore, UDPβS induced long-lasting contractions for more than 2 hours, explained by the low desensitization rate of the P2Y6 receptor. The ATP-induced vasoconstriction could not be abolished by desensitization of P2X1 receptors with αβ-MeATP, or P2Y2/4 receptors with UTPγS (uridine 5’-O-3-thiotriphosphate), indicating the presence of yet another contractile ATP receptor. Based on quantification with real-time polymerase chain reaction, the P2Y11 receptor could be responsible for this ATP contraction. Conclusions The P2X1 and P2Y6 receptors elicit more prominent contractions in the saphenous vein as compared with the internal mammary artery. These results may present one explanation for the differences in the two conduits. It is possible that selective antagonists of P2X1 and P2Y6 receptors could be used to prevent vasospasm and restenosis in the saphenous vein during and after revascularization surgery.