Differential effect of steady versus oscillating flow on bone cells

Loading induced fluid flow has recently been proposed as an important bioph ysical signal in bone mechanotransduction. Fluid flow resulting from activi ties which load the skeleton such as standing, locomotion, or postural musc le activity are predicted to be dynamic in nature and include a relatively small static component. However, in vitro fluid flow experiments with bone cells to date have been conducted using steady or pulsing How profiles only . In this study we exposed osteoblast-like hFOB 1.19 cells (immortalized hu man fetal osteoblasts) to precisely controlled dynamic fluid flow profiles of saline supplemented with 2% fetal bovine serum while monitoring intracel lular calcium concentration with the fluorescent dye fura-2. Applied Hows i ncluded steady How resulting in a wall shear stress of 2 N m(-2), oscillati ng flow (+/- 2 N m(-2)), and pulsing: flow (0 to 2 N m(-2)). The dynamic fl ows were applied with sinusoidal profiles of 0.5, 1.0, and 2.0 Hz. We found that oscillating flow was a much less potent stimulator of bone cells than either steady or pulsing How. Furthermore, a decrease in responsiveness wi th increasing frequency was observed for the dynamic Hows. In both cases a reduction in responsiveness coincides with a reduction in the net fluid tra nsport of the flow profile. Thus, these findings support the hypothesis tha t the response of bone cells to fluid flow is dependent on chemotransport e ffects. (C) 1998 Elsevier Science Ltd. All rights reserved.