Scanning Electrochemical Microscopy at the Surface of Bone‐Resorbing Osteoclasts: Evidence for Steady‐State Disposal and Intracellular Functional Compartmentalization of Calcium

• Published in: Journal of bone and mineral research 2001-11, Vol.16 (11), p.2092-2102
• Main Authors: Berger, Christine E. M., Rathod, Hersha, Gillespie, James I., Horrocks, Benjamin R., Datta, Harish K.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Bone Resorption - metabolism; Bone Resorption - pathology; Calcium - metabolism; Cattle; Cell Adhesion; Cell Compartmentation; cytosolic calcium; Electrochemistry - methods; Fundamental and applied biological sciences. Psychology; In Vitro Techniques; Microscopy, Electron, Scanning - methods; osteoclast activity; Osteoclasts - metabolism; Osteoclasts - ultrastructure; Rats; Rats, Wistar; scanning electrochemical microscopy; Skeleton and joints; superoxide anion; Superoxides - metabolism; Vertebrates: osteoarticular system, musculoskeletal system
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.2001.16.11.2092

Osteoclast resorptive activity occurs despite the presence of extremely high levels of ionized calcium ([Ca2+]) within the osteoclast hemivacuole, which is generated as a by‐product of its resorptive activity. Previous in vitro observations have shown that increases in extracellular [Ca2+] ([Ca2+]e) in the surrounding medium can inhibit the osteoclast resorptive activity. Therefore, it has been suggested that the osteoclast acts as a “sensor” for [Ca2+]e, and that high [Ca2+]e leads to an increase in intracellular [Ca2+] ([Ca2+]i), thereby inhibiting osteoclasts in a negative feedback manner. In this report we have carried out an experimental and theoretical analysis of calcium disposal during osteoclast activity to evaluate how in vitro models relate to in vivo osteoclast activity, where it is possible that high [Ca2+]e may be present in the hemivacuole but not over the nonresorbing surface of the cell. Scanning electrochemical microscopy (SECM) studies of [Ca2+] and superoxide anion () generation by bone‐resorbing osteoclasts on the surface of a bovine cortical bone slice were compared with microspectofluorometric measurements of the levels of [Ca2+]i in single osteoclasts and the effect of [Ca2+]i on various aspects of osteoclast function. The generation of by the osteoclasts has been shown to be positively correlated with osteoclast resorptive function and can therefore serve as an index of acute changes in osteoclast activity. The SECM of bone‐resorbing osteoclasts at the surface of a bone slice revealed a continuous steady‐state release of Ca2+. Even after prolonged incubation lasting 3 h the near‐surface [Ca2+]e in the solution above the cell remained