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

A. Miyauchi, K. A. Hruska, E. M. Greenfield, R. Duncan, J. Alvarez, R. Barattolo, S. Colucci, A. Zambonin-Zallone, S. L. Teitelbaum, A. Teti

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Abstract

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. Half-maximal effects were achieved at 70 mM K+. The effects of K+ were completely inhibited by dihydropyridine derivative Ca2+ channel blocking agents. BAY K 8644 (5 x l0-6 M), a VGCC agonist, stimulated Ca2+ entry which was inhibited by nicardipine. VGCCs were inactivated by the attachment of osteoclasts to bone, indicating a rapid phenotypic change in Ca2+ entry mechanisms associated with adhesion of osteoclasts to their resorption substrate. Increasing extracellular Ca2+ ([Ca2+](e)) induced Ca2+ release from intracellular stores and Ca2+ influx. The Ca2+ release was blocked by dantrolene (10-5 M), and the influx by La3+. The effects of [Ca2+](e) on [Ca2+](i) suggest the presence of a Ca2+ receptor on the osteoclast cell membrane that could be coupled to mechanisms regulating cell function. Expression of the [Ca2+](e) effect on [Ca2+](i) was similar in the presence or absence of bone matrix substrate. Each of the mechanisms producing increases in [Ca2+](i), (membrane depolarization, BAY K 8644, and [Ca2+](e)) reduced expression of the osteoclast-specific adhesion structure, the podosome. The decrease in podosome expression was mirrored by a 50% decrease in bone resorptive activity. Thus, stimulated increases of osteoclast [Ca2+](i) lead to cytoskeletal changes affecting cell adhesion and decreasing bone resorptive activity.

Original languageEnglish
Pages (from-to)2543-2552
Number of pages10
JournalJournal of Cell Biology
Volume111
Issue number6 I
DOIs
StatePublished - 1990

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