mRNA of the P2u purinoceptor (or nucleotide receptor) is detected both by polymerase chain reaction or Northern blot analyses in cultured aortic smooth muscle cells. When added to the culture medium of these cells, UTP, a specific ligand of the P2u receptor, induces an increased expression of both immediate-early and delayed-early cell cycle-dependent genes. This induction demonstrates similar features (kinetics, concentration dependence) to those obtained after stimulation of aortic smooth cells by exogenous ATP, a common ligand for most P2 purinoceptors. In contrast, 2-methylthioATP, a preferential ligand for P2y purinoceptors, induces only a significant increase of immediate-early genes but not of delayed-early genes. Moreover, the 2-methylthioATP-induced responses (c-fos mRNA increase, free intracellular calcium transient) are lower than those induced by ATP or UTP and are complementary to those of UTP. These results demonstrate that functional P2u receptors are present on cultured aortic smooth muscle cells and suggest that the bulk of responses induced by extracellular ATP on cell cycle progression are mediated via P2u purinoceptors, a hypothesis confirmed by cytofluorometric studies. Since some ATP- or UTP-induced genes code for chemotactic proteins (monocyte chemoattractant protein-1 and osteopontin), this study suggests that these nucleotides may contribute to vascular or blood cell migration and proliferation and consequently to the genesis of arterial diseases.