Bone adaptation to mechanical loading is dependent on age and the frequency and magnitude of loading. It is believed that load-induced fluid flow in the porous spaces of bone is an important signal that influences bone cell metabolism and bone adaptation. We used fluid flow-induced shear stress as a mechanical stimulus to study intracellular calcium (Ca2+i) signaling in rat osteoblastic cells (ROB) isolated from young, mature, and old animals. Fluid flow produced higher magnitude and more abundant [Ca2+]ioscillations than spontaneous oscillations, suggesting that flow-induced Ca2+i signaling encodes a different cellular message than spontaneous oscillations. ROB from old rats showed less basal [Ca2+]i activity and were less responsive to fluid flow. Cells were more responsive to 0.2 Hz than to 1 or 2 Hz and to 2 Pa than to 1 Pa. These data suggest that the frequency and magnitude of mechanical loading may be encoded by the percentage of cells displaying [Ca2+]i oscillations but that the ability to transduce this information may be altered with age.
mechanotransduction; osteoblast; calcium signaling; bone adaptation