ANTITHETIC EFFECTS OF RYANODINE AND RUTHENIUM RED ON OSTEOCLAST-MEDIATED BONE-RESORPTION AND INTRACELLULAR CALCIUM CONCENTRATIONS

In the process of bone remodeling, osteoclasts are responsible for res orption of bone. High levels of intracellular calcium decrease the bon e resorbing activity of osteoclasts and increase detachment of osteocl asts from the bone surface. The regulatory role of intracellular calci um in bone resorption is not clearly understood. To understand this ph enomenon, we studied the effects of the intracellular calcium modulato rs ryanodine and ruthenium red on bone resorption using the disaggrega ted osteoclast pit assay. Changes in intracellular calcium concentrati ons after treatment with these compounds were detected with the fluoro probe fura2. With ryanodine, a significant, dose-dependent decrease in bone resorption was detected. This inhibition of bone resorption was reversible upon the removal of ryanodine. Ryanodine increased intracel lular calcium concentrations, suggesting that the mechanism of inhibit ion by ryanodine was via alterations in intracellular stores of calciu m. After treatment with ruthenium red, osteoclasts resorbed significan tly more bone compared to vehicle-treated cells. This increase in bone resorption correlated with a decrease in intracellular calcium concen trations. The addition of parathyroid hormone or ruthenium red to oste oclast cultures containing ryanodine did not attenuate the decrease in bone resorption caused by ryanodine, suggesting that the mechanism of ryanodine inhibition of bone resorption may involve the ''locking'' o f a calcium channel in an open position. (C) 1995 Wiley-Liss, Inc.