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 intracellular Ca(2+). 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 Ca(2+) is high after treating with ATP, cyclopiazonic acid and thapsigargin, stimulation causes a transient decrease in Ca(2+). In these three cell types, no influx of ions is required for Ca(2+) 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 Ca(2+). The Ca(2+) 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 IP(3)-activated channels. Despite the lack of a causal involvement of plasmalemmal mechanosensitive channels, mechanical stimulation immediately activates a persistent Mn(2+) influx pathway. This Mn(2+) pathway may be mechanosensitive channels, Ca(2+)-activated cation channels or depletion-activated Ca(2+) channels.