Mechanical stimulation induces intercellular calcium signaling in bovine aortic endothelial cells

To study the mechanism by which endothelial cells respond to mechanical forces, we used digital fluorescence microscopy to measure changes in intracellular Ca2+ concentration ([Ca2+]i) in primary cultures of bovine aortic endothelial cells in response to mechanical stimulation. Before stimulation, [Ca2+]i was stable (approximately 50-75 nM). When an individual cell within the monolayer was mechanically stimulated with a microprobe, [Ca2+]i increased in the stimulated cell and spread in the form of a wave from the site of contact to the cell edges. After a delay of approximately 1 s, nonstimulated adjacent cells showed a similar spreading rise in [Ca2+]i. This outwardly radiating [Ca2+]i wave involved progressively more distal cells to a radius of 4-6 cells. The time delay before the wave appeared in adjacent cells increased, and peak [Ca2+]i in each cell decreased with distance from the stimulated cell. In the absence of extracellular Ca2+, there was no increase in [Ca2+]i in the stimulated cell, yet a wave of increased [Ca2+]i occurred in neighboring cells as if communicated from the stimulated cell. These results indicate that endothelial cell mechanosensitivity results in increases in [Ca2+]i and that the temporospatial dynamics of intercellular Ca2+ signaling are mediated by a diffusible substance other than Ca2+.