P2Y receptor-mediated Ca2+ signaling increases human vascular endothelial cell permeability

We investigated the effects of P2-receptor agonists on cell size, intracellular calcium levels ([Ca2+](i)), and permeation of FITC-labeled dextran (FD-4) as well as the relationship between these effects in human umbilical vein endothelial cells (HUVEC). FD-4 concentration, cell size, and [Ca2+], were analyzed by HPLC with fluorescence, phase contrast microscopic imaging, and fluorescent confocal microscopic imaging, respectively. The P2Y(1)-receptor agonists 2-methylthio ATP (2meS-ATP) and ADP decreased cell size and increased [Ca2+](i) in HUVEC. The P2Y(2)-receptor agonist UTP increased [Ca2+](i), but did not influence cell size. The P2X-receptor agonist alpha,beta-methylene ATP did not induce either response. The decrease in size and increase in [Ca2+](i) by 2meS-ATP were blocked by pyridoxalphosphate-6-azophenyl-2',4'disulphonic acid (PPADS, P2Y(1)-antagonist), thapsigargin (Ca2+-pump inhibitor), and U73122 (phospholipase C inhibitor). Furthermore, 2meS-ATP (P2Y(1)-receptor agonist) enhanced permeation of FD-4 through the endothelial cell monolayer. The 2meS-ATP-induced enhancement of the permeation was also prevented by PPADS, thapsigargin, and U73122. These results indicate that activation of P2Y receptors induces a decrease in cell size, an increase in [Ca2+] i, and may participate in facilitating macromolecular permeability in HUVEC.