Spontaneous and stimulated transients in cytoplasmic free Ca2+ in normal human osteoblast-like cells: Aspects of their regulation

We characterize two patterns of transients in cytoplasmic free calcium ([Ca 2+](i)) in normal human osteoblast-like cells (hOB cells). Firstly, spontan eous oscillations in [Ca2+](i) were found to be common. The [Ca2+](i) oscil lations were completely inhibited by thapsigargin, indicating that Ca2+ flu xes between intracellular Ca2+ pools and the cytosol contributed to the gen eration of the [Ca2+](i) oscillations. Removing extracellular Ca2+ either a ttenuated or completely inhibited spontaneous [Ca2+](i) oscillations. Gadol inium, an inhibitor of stretch activated cation channels (SA-cat channels), reduced the frequency of [Ca2+](i) oscillations. Hence, entry of calcium f rom the extracellular space, possibly through SA-cat channels also seemed t o be of importance in the regulation of these [Ca2+](i) oscillations. The r ole of the observed spontaneous [Ca2+](i) oscillations in hOB cell function is not clear. Secondly, a decrease in pericellular osmolality, which cause s the plasma membrane to stretch, transiently increased [Ca2+](i) in hOB ce lls. This effect was also observed in a Ca2+ free extracellular environment , suggesting that osmotic stimuli release Ca2+ from intracellular pools. Th is finding indicates a possible signaling pathway by which mechanical strai n can promote anabolic effects on the human skeleton. (C) 1999 Academic Pre ss.