Osteocalcin induces chemotaxis, secretion of matrix proteins, and calcium-mediated intracellular signaling in human osteoclast-like cells.

Osteocalcin, also called Bone Gla Protein (BGP), is the most abundant of the non-collagenous proteins of bone produced by osteoblasts. It consists of a single chain of 46-50 amino acids, according to the species, and contains three vitamin K-dependent gamma-carboxyglutamic acid residues (GLA), involved in its binding to calcium and hydroxylapatite. Accumulating evidences suggest its involvement in bone remodeling, its physiological role, however, is still unclear.

Functional and biochemical characterization of osteoclast-like cells derived from giant cell tumours of bone.

Cells harvested from human giant cell tumours of bone were characterized on the basis of morphological features, proliferative capacity, total(AP) and tartrate resistant acid phosphatase (TRAP) activity, and hormonal response. Culture were formed by mononucleated and multinucleated cells. Mononucleated cells showed fibroblastic morphology, whereas multinucleated cells showed osteoclastic phenotype.

Protein kinase C-dependent phosphorylation regulates osteoclast calcium-sensing.

Osteoclasts display a membrane Ca(2+)-sensing mechanism capable of detecting the extracellular calcium concentration ([Ca2+]o), and to induce increase of [Ca2+]i and inhibition of bone resorption. The ultimate result of the stimulation of such sensing is probably the activation of protein kinase C (PKC). To demonstrate whether PKC plays a role in the control of the osteoclast activity, we treated rabbit single osteoclasts with agents known to activate or to inhibit the enzyme.

Osteoclast cytosolic calcium, regulated by voltage-gated calcium channels and extracellular calcium, controls podosome assembly and bone resorption.

The mechanisms of Ca2+ entry and their effects on cell function were investigated in cultured chicken osteoclasts and putative osteoclasts produced by fusion of mononuclear cell precursors. Voltage-gated Ca2+ channels (VGCC) were detected by the effects of membrane depolarization with K+, BAY K 8644, and dihydropyridine antagonists. K+ produced dose-dependent increases of cytosolic calcium ([Ca2+]i) in osteoclasts on glass coverslips.

Cytosolic free calcium dependent regulation of osteoclast bone resorbing activity.

Osteoclasts are sensitive to KCl-induced depolarization and to increased extracellular calcium concentration, and respond to these treatments with cytosolic calcium increase. In this study we evaluated the possibility that these experimental conditions could affect osteoclast bone resorption. We found that, incubating osteoclasts with 3H-proline previously labeled bone particles the resorbing activity was inhibited by both depolarization and extracellular calcium concentration increase.