Effects of fluid flow on intracellular calcium in bovine articular chondrocytes

Fluid flow-induced shear stress results in a variety of morphological and metabolic changes in cultured bovine articular chondrocytes (BAC), However, the mechanism by which the flow Signal is transduced into a biological response is unknown. Therefore, we investigated the effects of fluid flow on intracellular Ca2+ concentration ([Ca2+](i)) in BAG. Cells loaded with fara 2 were exposed to steady and pulsatile (0.5 Hz) flow at 9, 18, and 34 ml/min in a parallel-plate flow chamber. In response to flow there was a significant and flow rate-dependent increase in the percentage of cells showing a rise in [Ca2+](i) but no effect on the [Ca2+](i) response amplitude. There was no significant difference between the [Ca2+](i) responses to steady and pulsatile flow. Mean intracellular Ca2+ response values ranged between 26.2 +/- 1.6 (9 ml/min) and 38.0 +/- 6.8 nM (34 ml/min) above basal [Ca2+](i) (81.3 +/- 24.1 nM, n = 90). Removal of extracellular Ca2+ or addition of Gd3+ significantly reduced the percentage of cells responding, suggesting that influx of Ca2+ possibly through mechanosensitive channels, contributes td the rise in intracellular Ca2+. Our data suggest fluid flow-induced mobilization of intracellular Ca2+ may contribute to the mechanism by which mechanical loads are transduced by chondrocytes.