ab22207

Modulation of intracellular calcium signaling and mitochondrial function in cultured osteoblastic cells by dexamethasone and celecoxib during mechanical stimulation

S. Schuchmann, M. Wiontzek, G.-R. Burmester, F. Buttgereit

Medizinische Klinik mit Schwerpunkt Rheumatologie und Klinische Immunologie, Universitätsklinikum Charité, Humboldt Universität Berlin, Germany.

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

Methods
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 (DY_m). Microfluorometric techniques were applied to monitor [Ca²⁺]_i (Fura-2 AM) and DY_m (rhodamine 123) online as the main parameters of the actual cellular metabolism.

Results
Basal [Ca²⁺]_i was found to be 92.2 ± 3.7 nM and increased up to 711 ± 27 nM during mechanical stimulation under controlled conditions. Addition of 100 nM dexamethasone or 10 µM 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.

Conclusion
The observed effects of dexamethasone and celecoxib on mechanically induced changes in [Ca²⁺]_i and DY_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.

Key words
Osteoblast, mechanical stimulation, intracellular Ca²⁺ concentration, mitochondrial membrane potential, gap junction, glucocorticoid, celecoxib.

This study was supported by a grant from Pharmacia.
Please address correspondence to: Dr. Sebastian Schuchmann Institut für Diagnostische Radiologie und Neuroradiologie, Ernst-Moritz-Arndt-Universität Greifswald, Friedrich-Loeffler-Str. 23a, 17487 Greifswald, Germany.
E-mail: sebastian.schuchmann@uni-greifswald.de