Bone cells can be exposed to high calcium in the course of endodontic treatment. To investigate the effects of high calcium on bone cell function, responses of a rat osteoblast cell line (UMR 106) were examined. Responsiveness of the cells to parathyroid hormone, prostaglandin F1α, and ionomycin was assessed by measuring calcium transients elicited by these stimuli. Raising the medium calcium from 1.8 to 50 mm did not alter cell responsiveness. Pretreatment of the cells with the calcium pump inhibitor sodium vanadate prevented parathyroid hormone effects and slightly decreased prostaglandin F1α effects in both normal and high calcium. The effect of ionomycin was prolonged in high calcium when vanadate was present. The results suggest that cells of the osteoblast phenotype can maintain calcium signaling in the presence of high extracellular calcium. These processes could play a role in the therapeutic effectiveness of high calcium in endodontic treatment.
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