Modulation of Ca2+ transients in cultured endothelial cells in response to fluid flow through αv integrin

In order to determine whether integrin dynamics is associated with intracellular Ca2+ concentration ([Ca2+]i) mobilization in ECs in response to hemodynamic forces, changes in [Ca2+]i in fluo-4-loaded cultured bovine aortic endothelial cells (BAECs) under fluid flow conditions were visualized employing laser scanning confocal microscopy. Following the onset of flow stimulus, transient increases in [Ca2+]i occurred several times in individual BAECs during the 30-min observation period. The frequency of these [Ca2+]i transients was clearly reduced by the application of an integrin antagonist (GRGDSP peptide). Furthermore, treatment of cells with an integrin activator (Mn2+) resulted in reduction of peak [Ca2+]i levels and elevated frequency, which was markedly rescued upon GRGDSP administration. In contrast, an actin de-polymerizing agent (cytochalasin D) exerted no inhibitory effects; rather, cytochalasin D more likely facilitated [Ca2+]i transients. Moreover, [Ca2+]i transients, which were suppressed by short interference RNA-induced silencing of αv integrin, exhibited greater frequently in cells cultured on vitronectin substratum in comparison with those cultured on fibronectin or collagen substratum. Either removal of extracellular Ca2+, application of an inhibitor of endoplasmic reticulum Ca2+-ATPase (thapsigargin) or non-selective cation channel blocker (La3+) inhibited the [Ca2+]i transients. Additionally, [Ca2+]i transients were attenuated by extracellular signal-regulated kinase (ERK) kinase inhibitor (U0126); in contrast, [Ca2+]i transients were unaffected by tyrosine kinase inhibitor (genistein) or phosphatidylinositol 3-kinase (PI3K) inhibitor (LY294002). Therefore, our findings revealed that αv integrin dynamics modulates the frequency of flow-induced [Ca2+]i transients in BAECs in an ERK-dependent fashion.