Flow-induced calcium oscillations in rat osteoblasts are age, loading frequency, and shear stress dependent

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 (Ca${}_{\text{i}}^{2+}$ ) 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 Ca${}_{\text{i}}^{2+}$ 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⁺]_ioscillations but that the ability to transduce this information may be altered with age.