REAL-TIME CALCIUM RESPONSE OF CULTURED BONE-CELLS TO FLUID-FLOW

Using a parallel-plate pow chamber and fura-2 fluorescence microscopy, intracellular calcium was measured cell by cell in preconfluent prima ry culture rat calvarial bone cells to 18, 35, and 70 dynes/cm(2) of f luid-induced shear stress. A heterogeneous response with respect to pe ak amplitude and latency was observed for the culture, with an overrid ing dose-dependent relationship between the mean peak amplitude of res ponse and shear-stress magnitude. A dose dependence was observed betwe en the number of responsive cells (responding >50% over basal levels) and shear-stress magnitude. Not all cells could be restimulated by rep eated exposure to pow. The observed cell response appears to be indepe ndent of whether cells are clustered together or isolated. Substratum stretch, hydrostatic pressure, and fluid shear stress have been shown in the literature to increase inositol phosphate (IP3) in bone cells, with IP3 causing the release of calcium from intracellular stores such as the endoplasmic reticulum. Therefore, a 6-fold inhibitory effect o bserved when calcium release from stores was blocked with 8-(n,N-dieth ylamino)octyl 1-3,4,5-atrimethoxybenzoate hydrochloride implicates an IP3 biochemical pathway mediating the fluid flow response in bone cell s.