Extracellular nucleotides, particularly ATP, are involved in the modulation of arterial vasomotricity via P2 purinoceptors present on smooth muscle and endothelial cells. These nucleotides could also be implicated in the smooth muscle cell hyperplasia observed in intimal lesions. In this study, we tried to define the potential role of the P2Y2 (P2u) purinoceptor by studying its expression in normal and balloon-injured rat aortas. The cloning of a rat P2Y2 cDNA from a rat smooth muscle cell cDNA library made it possible to study P2Y2 expression both by Northern blot and in situ hybridization. Northern blot experiments indicated that P2Y2 mRNA was present in rat medial aortic smooth muscle and in cultured rat aortic smooth muscle cells. In situ hybridization indicated that P2Y2 mRNA was present in endothelial cells of the intima and in some smooth muscle cells scattered throughout the media of adult rat aortas, while almost all medial smooth muscle cells of rat embryo aorta expressed this receptor. In contrast with adult aortic media, the majority of neointimal smooth muscle cells found in aortic intimal lesions either 8 or 20 days after balloon injury were positive for P2Y2 mRNA. Moreover, a subpopulation of neointimal cells localized at the luminal surface could be identified by a higher P2Y2 expression than the underlying neointimal smooth muscle cells. These data showing a strong expression of the P2Y2 purinoceptor in the neointima of injured arteries suggest that extracellular nucleotides may be involved, via this receptor, in the intimal hyperplasia and/or chronic constriction observed at the lesion site, and consequently in the restenotic process.

Abstract-Many factors have been shown to be involved in the development of hyperplasic lesions of vessels, but the role of extracellular nucleotides remains largely unknown. The presence of P2Y and P2X nucleotide receptors on arterial endothelial and smooth muscle cells suggests a potential role for nucleotides in the vessel pathophysiology. Although the role of P2X in physiology of vessels is well documented, that of P2Y is not completely understood. We recently demonstrated that extracellular nucleotides, and particularly UTP, induced migration of cultured arterial smooth muscle cells (ASMCs). This migration is dependent on osteopontin expression and involves the Rho and mitogen-activated protein (MAP) kinase pathways. An important question is to determine the specific role of the different P2Y receptors of rat ASMCs in the UTP-induced migration process. Therefore, we first quantified mRNA levels of P2Y 2 , P2Y 4 , and P2Y 6 nucleotide receptors in cultured rat ASMCs by a competitive RT-PCR approach and demonstrated that P2Y 2 is the most highly expressed among these receptors potentially involved in the UTP-mediated response. In addition to UTP, UDP also induced ASMC migration even when UTP regeneration was inhibited, suggesting the involvement of UDP receptor P2Y 6 . Moreover, suramin, a specific antagonist of rat P2Y 2 receptor, acted as an inhibitor of UTP-induced migration. Taken together, these results suggest a prominent role for the UTP receptor, P2Y 2 , and for the UDP receptor, Key Words: purinergic receptors Ⅲ migration Ⅲ UTP Ⅲ smooth muscle cells T he important role of arterial smooth muscle cell (ASMC) migration and proliferation in arterial hyperplasia is well documented in experimental models for atherosclerosis and restenosis. 1 Although proliferation can be easily demonstrated in arterial injury models, evidence for in vivo ASMC migration is suggested only by the presence of these cells in the intima.Many factors have been shown to be involved in the development of hyperplasic lesions of vessels. 2 Among these, the role of extracellular nucleotides remains largely unknown. Two families of receptors have been identified for these compounds: inotropic P2X receptors and metabotropic P2Y receptors. The presence of P2Y and P2X receptors on endothelial and ASMCs suggests a potential role for nucleotides in the arterial pathophysiology. Although the role of P2X receptors in vasomotoricity of vessels is well documented, that of P2Y receptors in the vessel wall is still under investigation.Several studies have shown that ATP and UTP binding to P2Y G protein-coupled receptors mediates ASMC activation, 3 cell-cycle progression, 4 and cell proliferation. 5,6 Moreover, we recently demonstrated that UTP induces ASMC migration and that this migration is dependent on osteopontin expression and involves the Rho and mitogen-activated protein (MAP) kinase pathways. 7 The overexpression of the ATP/UTP P2Y 2 receptor in ASMCs of rat aortic intimal lesion 8 and in ASMCs of human coronary atherosclerotic/restenotic ...

beta1- and beta2-AR, but not beta3-AR, mediate relaxation of mice pulmonary arteries. The beta2-AR component is dependent on eNOS activity and is preserved following chronic hypoxia. These data highlight the role of the beta2-AR as a pharmacological target to induce/restore endothelial NO-dependent protective effects in pulmonary circulation.