Journal of Bone and Mineral Research

Abstract

We examined the effect of fluoride (F) on intracellular ionic calcium [Ca²⁺]_i in normal human osteoblasts maintained in culture. Cells were grown on glass coverslips to near-confluency and loaded with the Ca-sensitive dye, fura-2AM. Fluorescence changes were monitored in single cells using an inverted microscope coupled by fiberoptic to a microspectrofluoremeter. The addition of F (100 ng/mL) to the medium promoted a rapid and significant increase in free [Ca²⁺]_i from a resting level of 245 ± 36 SE nM to a peak concentration of 440 ± 51 nM (p < 0.04). This increase in [Ca²⁺]_i began at 10–20 s after addition of F and was maximal by 30 s. Intracellular [Ca²⁺]_i levels then returned to near resting values by 60–80 s after F addition. This response was evident with as little as 25 ng/ml of fluoride and was dose dependent up to 500 ng/ml. At concentrations greater than 500 ng/ml, there appeared to be an attenuation of the rise in [Ca²⁺]_i. The observed rise in [Ca²⁺]_i was dependent on extracellular calcium since lowering extracellular calcium concentration or incubation with calcium channel blockers abolished the response. This observation supports a role of increased [Ca²⁺]_i as one of the initial events of fluoride on action osteoblasts.