Serum Modulates the Intracellular Calcium Response of Primary Cultured Bone Cells to Shear Flow

We investigated the effect of newborn bovine serum on the intracellular calcium [Ca(2+)](i) response of primary cultured bone cells stimulated by fluid flow. As it has been previously established that these cells exhibit [Ca(2+)](i) responses to fluid flow shear stress in saline media without growth factors or other chemically stimulatory factors, we hypothesized that the addition of serum to the flow medium would enhance the mechanosensitivity of the cells. We examined the effect of a short-term (10-15min) exposure of the cells to 2 and 10% serum prior to flow stimulation (pretreated) compared to not exposing the cells prior to flow stimulation (unpretreated). The cells were subjected to a well-defined, 90-s flow stimulus with shear stress levels ranging from 0.02 to 3.5Pa in a laminar flow chamber using a saline medium supplemented with 2 or 10% serum. For pretreatment, the serum concentration was the same from pre-flow to flow exposure. We observed a differential effect in the magnitude of the peak [Ca(2+)](i) response modulated by the concentration of serum in the pre-flow medium. Additionally, ATP-supplemented flow was examined as a comparison to the serum-supplemented flow and exhibited a similar trend in the peak [Ca(2+)](i) flow response that was dependent on ATP concentration and pre-flow exposure conditions. These findings demonstrate that under the conditions of this study, chemical agonist exposure can modulate the [Ca(2+)](i) response in bone cells subjected to fluid flow-induced shear stress.