Modulation of intracellular calcium signaling and mitochondrial function in cultured osteoblastic cells by...

Evaluation of potentially therapeutically relevant effects of dexamethasone and celecoxib on crucial parameters of bone physiology during and following mechanical stimulation in cultured osteoblasts.

An in vitro mechanical stimulation model based on the rat osteogenic cell line UMR-106 was developed to investigate glucocorticoid (dexamethasone) and selective COX-2 inhibitor (celecoxib) induced changes in the intracellular calcium concentration ([Ca2+]i) and mitochondrial membrane potential (deltapsi(m)). Microfluorometric techniques were applied to monitor [Ca2+]i (Fura-2 AM) and deltapsi(m) (rhodamine 123) online as the main parameters of the actual cellular metabolism.

Basal [Ca2+] was found to be 92.2 +/- 3.7 nM and increased tip to 711 +/- 27 nM during mechanical stimulation under controlled conditions. Addition of 100 nM dexamethasone or 10 microM celecoxib for 24 h suppressed the increase in [Ca2+]i significantly to 530 +/- 33 nM and 546 +/- 39 nM, respectively. Dexamethasone significantly reduced, but celecoxib significantly increased the spread velocity of the mechanically induced intracellular calcium wave. Furthermore, the effects induced by dexamethasone were amplified during the inhibition of gap junction coupling and diminished following enlarged gap junction coupling. In contrast, the modulation of gap junction coupling exerted only a minor influence on the celecoxib-induced effects. Short-term application of dexamethasone (5 min) caused significantly reduced mechanically induced depolarization of the mitochondrial membrane, but long-term application (24 h) did not. In contrast, only the long-term application (24 h) of celecoxib caused such depolarization.

The observed effects of dexamethasone and celecoxib on mechanically induced changes in [Ca2+] and deltapsi(m) are suggested to result from short-term changes in membrane characteristics and long-term changes in protein synthesis. This indicates an influence of these drugs on cell-to-cell communication and metabolism that may be therapeutically relevant.