Shear-stress sensing via P2 purinoceptors in vascular endothelial cells

Abstract

The mechanisms by which shear stress elevates intracellular Ca2+ in endothelial cells (EC) are not fully understood. Here we report that endogenously released ATP contributes to shear stress-induced Ca2+ responses. Application of a flow of Hank's balanced solution to human pulmonary artery EC (HPAEC) elicited shear stress-dependent increases in Ca2+ concentration. Chelation of extracellular Ca2+ with EGTA completely abolished the Ca2+ responses, whereas the phospholipase C inhibitor U-73122 and the Ca2+-ATPase inhibitor thapsigargin had no effect, indicating that the response was due to the influx of extracellular Ca 2+. The Ca2+ influx was significantly suppressed by apyrase, which degrades ATP, and by antisense oligonucleotide targeted to P2X4 receptors. A luciferase luminometric assay showed that shear stress induced dose-dependent release of ATP. When the ATP release was inhibited by the ATP synthase inhibitors angiostatin or oligomycin, the Ca2+ influx was markedly suppressed but was restored by removal of these inhibitors or addition of extracellular ATP. These results suggest that shear stress stimulates HPAEC to release ATP, which activates Ca2+ influx via P2X4 receptors.