Extracellular nucleotides are involved in the development of vascular inflammation. However, little is known about whether effects of nucleotides are modulated under inflammatory states. We investigated effects of interferon-gamma (INF-gamma) on ATP-induced responses in vascular endothelial cells. Treatment of human umbilical vein endothelial cells (HUVECs) with IFN-gamma for 24 h resulted in an enhancement of the ATP-induced increase in intracellular Ca2+ concentration ([Ca2+]i) without affecting the UTP-induced one. The increased Ca2+ response to ATP in IFN-gamma-treated cells was dependent on the extracellular Ca2+, and was not inhibited by the phospholipase C inhibitor U73122. RT-PCR and Western blotting revealed that HUVECs dominantly expressed P2X4 receptor. IFN-gamma increased P2X4-receptor mRNA and protein, accompanied by an increase in ATP-triggered membrane current. IFN-gamma did not affect P2X4-receptor mRNA stability, but increased P2X4-receptor gene transcription in a cycloheximide-insensitive manner. IFN-gamma stimulated phosphorylation of signal transducer and activator of transcription-1 (STAT1). Epigallocatechin gallate (EGCG), an inhibitor of STAT1-mediated signaling, and AG490, a Janus kinase (JAK) inhibitor, impaired P2X4-receptor mRNA up-regulation by IFN-gamma. These results indicate that INF-gamma selectively increases P2X4-receptor gene expression, leading to an up-regulation of purinergic signaling in vascular endothelial cells.