Endothelial cell spreading on type IV collagen and spreading-induced FAK phosphorylation is regulated by Ca2+ influx

The interaction of endothelial cells with their basement membrane and local stroma is highly regulated. The observation that CAI, an inhibitor of Ca++ influx, inhibited human umbilical vein endothelial cell (HUVEC) adhesion suggested that Ca++ influx was a regulator of HUVEC-matrix interaction. Exposure of HUVEC cells to CAI or SK&F 96365, another Ca++ influx inhibitor, selectively blocked spreading but not attachment on type IV collagen but not type I collagen. Ca++ influx blockade also prevented spreading-induced FAK phosphorylation and kinase activity and secondary paxillin phosphorylation. No inhibitory effect was observed when the cells spread on type I collagen. The inhibitory effect of CAI on spreading and spreading-associated FAK phosphorylation and kinase activity was reversible. These data indicate that HUVEC cells have a selective requirement for Ca++ influx for spreading and downstream signaling on basement membrane type IV collagen.