Localized calcium signaling in multinucleated osteoclasts

Localized intracellular Ca²⁺ (Ca²⁺]_i) pulses, fluctuations, and repetitive spikes were detected in multinucleated rabbit osteoclasts in the presence of serum and in response to calcitonin using the fluorescent calcium indicator fluo-3 and a laser scanning microscope. We observed that these Ca²⁺]_i changes were often restricted within a region of the cell body or propagated from the initial region of occurrence to other parts of the cell body but not to all parts. These observations suggest the existence of significant barriers to Ca²⁺ transport between different cytoplasmic regions of the osteoclast. To further investigate this phenomenon, we mechanically perturbed different cellular regions by touching locally with a micropipette. This usually induced a local increase in cytosolic and nuclear free Ca²⁺]_i. In some cases there was propagation of the Ca²⁺]_i increase to other regions but with part of the cell body not affected. Those regions of the cell body to which the Ca²⁺]_i increase did not propagate had a Ca²⁺]_i response to a direct mechanical perturbation. Our data show that osteoclasts can have different Ca²⁺]_i activities in apparently equivalent cellular regions, no matter how generated. This suggests that there can be a number of spatially separate Ca²⁺ regulatory systems within an osteoclast cell body. © 1996 Wiley-Liss, Inc.