Mechanically induced calcium movements in astrocytes, bovine aortic endothelial cells and C6 glioma cells

Forces applied to resting primary astrocytes, bovine aortic endothelial cel ls and C6 glioma cells with collagen-coated magnetite particles produce a f ast transient change of intsacellular Ca2+. It peaks in the micromolar rang e as measured by Fura-2. This mechanical response adapts within seconds so that repeated stimulation causes smaller responses requiring >10 min for re covery. When cytoplasmic Ca2+ is high after treating with ATP, cyclopiazoni c acid and thapsigargin, stimulation causes a transient decrease in Ca2+. In these three cell types, no influx of ions is required for Ca2+ elevation showing the response is not caused by activation of plasmalemmal mechanose nsitive channels. Approximately half the cells tested showed similar behavi or, while the other half, such as fibroblasts, required extracellular Ca2+. The Ca2+ response is not temperature sensitive suggesting the possible inv olvement of intracellular mechanosensitive channels. We tested a number of second messenger reagents and were only able to block the response in BAECs , but not C6 glioma cells, with Xestospongin C, a blocker of IP3-activated channels. Despite the lack of a causal involvement of plasmalemmal mechanosensitive c hannels, mechanical stimulation immediately activates a persistent Mn2+ inf lux pathway. This Mn2+ pathway may be mechanosensitive channels, Ca2+-activ ated cation channels or depletion-activated Ca2+ channels.