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.