Fluid Shear Stress Activates Ca2+ Influx Into Human Endothelial Cells via P2X4 Purinoceptors

Abstract—Ca2+ signaling plays an important role in endothelial cell (EC) responses to shear stress generated by blood flow. Our previous studies demonstrated that bovine fetal aortic ECs showed a shear stress–dependent Ca2+ influx when exposed to flow in the presence of extracellular ATP. However, the molecular mechanisms of this process, including the ion channels responsible for the Ca2+ response, have not been clarified. Here, we demonstrate that P2X4 purinoceptors, a subtype of ATP-operated cation channels, are involved in the shear stress–mediated Ca2+ influx. Human umbilical vein ECs loaded with the Ca2+ indicator Indo-1/AM were exposed to laminar flow of Hanks’ balanced salt solution at various concentrations of ATP, and changes in [Ca2+]i were monitored with confocal laser scanning microscopy. A stepwise increase in shear stress elicited a corresponding stepwise increase in [Ca2+]i at 250 nmol/L ATP. The shear stress–dependent increase in [Ca2+]i was not affected by phospholipase C inhibitor (U-73...