P2 receptor expression profiles in human vascular smooth muscle and endothelial cells

P2 receptors mediate the actions of,the extracellular nucleotides ATP, ADP, UTP, and UDP, regulating several physiologic responses including cardiac function, vascular tone, smooth muscle cell (SMC) proliferation, platelet aggregation, and the release of endothelial factors. P2 receptor characterization has been hampered by the lack of selective antagonists. The aim of the current study was to investigate the mRNA and protein expression of P2X and P2Y receptors in human SMC and in endothelial cells (EC). Smooth muscle cells were obtained from human mammary artery and EC from human umbilical vein. Using real-time PCR, the authors established quantitative mRNA assays. Protein expression was studied using Western blotting with recently developed antibodies. The P2X(1) receptor was highly specific for human SMC, while the P2X(4) was the highest expressed receptor in EC. The P2Y(2) receptor was present in both SMC and EC. UTP-mediated effects in these cells are likely to be mediated by P2Y(2) and not P2Y(4) receptors since the latter had considerably lower expression. The P2Y(6) receptor was expressed in both SMC and EC. The P2Y(1) and surprisingly the P2Y(11) receptors were the most abundantly expressed P2Y receptors in the endothelium. Overall, Western blotting confirmed the mRNA findings in most aspects, and most interestingly, indicated oligomerization of the P2Y(1) receptor that may be important for its function. In conclusion, P2X(1), P2Y(2), and P2Y(6) are the most expressed P2 receptors in SMC and are thus probably mediating the contractile and mitogenic actions of extracellular nucleotides. The P2X(4), P2Y(11), P2Y(1), and P2Y(2) are the most expressed P2 receptors in EC, and are most likely mediating release of nitric oxide, endothelium-dependent hyperpolarizing factor (EDHF), and t-PA induced by extracellular nucleotides. These findings will help to direct future cardiovascular drug development against the large P2 receptor family.