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

Forces applied to resting primary astrocytes, bovine aortic endothelial cells and C6 glioma cells with collagen-coated magnetite particles produce a fast transient change of intsacellular Ca2+. It peaks in the micromolar range as measured by Fura-2. This mechanical response adapts within seconds so that repeated stimulation causes smaller responses requiring >10 min for recovery. When cytoplasmic Ca2+ is high after treating with ATP, cyclopiazonic 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 mechanosensitive channels. Approximately half the cells tested showed similar behavior, while the other half, such as fibroblasts, required extracellular Ca2+. The Ca2+ response is not temperature sensitive suggesting the possible involvement 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 channels, mechanical stimulation immediately activates a persistent Mn2+ influx pathway. This Mn2+ pathway may be mechanosensitive channels, Ca2+-activated cation channels or depletion-activated Ca2+ channels.