Mechanism and role of high-potassium-induced reduction of intracellular Ca2+ concentration in rat osteoclasts

Hiroshi Kajiya, Fujio Okamoto, Hidefumi Fukushima, Keisuke Takada, Koji Okabe

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Osteoclasts are multinucleated, bone-resorbing cells that show structural and functional differences between the resorbing and nonresorbing (motile) states during the bone resorption cycle. In the present study, we measured intracellular Ca2+ concentration ([Ca2+]i) in nonresorbing vs. resorbing rat osteoclasts. Basal [Ca2+]i in osteoclasts possessing pseudopodia (nonresorbing/motile state) was around 110 nM and significantly higher than that in actin ring-forming osteoclasts (resorbing state, around 50 nM). In nonresorbing/motile osteoclasts, exposure to high K+ reduced [Ca2+]i, whereas high K+ increased [Ca2+]i in resorbing state osteoclasts. In nonresorbing/motile cells, membrane depolarization and hyperpolarization applied by the patch-clamp technique decreased and increased [Ca2+]i, respectively. Removal of extracellular Ca2+ or application of 300 μM La3+ reduced [Ca2+], to ∼50 nM in nonresorbing/motile osteoclasts, and high-K+-induced reduction of [Ca2+]i could not be observed under these conditions. Neither inhibition of intracellular Ca2+ stores or plasma membrane Ca2+ pumps nor blocking of L- and N-type Ca2+ channels significantly reduced [Ca2+]i. Exposure to high K+ inhibited the motility of nonresorbing osteoclasts and reduced the number of actin rings and pit formation in resorbing osteoclasts. These results indicate that in nonresorbing/motile osteoclasts, a La3+-sensitive Ca2+ entry pathway is continuously active under resting conditions, keeping [Ca2+]i high. Changes in membrane potential regulate osteoclastic motility by controlling the net amount of Ca2+ entry in a "reversed" voltage-dependent manner, i.e., depolarization decreases and hyperpolarization increases [Ca2+]i.

Original languageEnglish
JournalAmerican Journal of Physiology - Cell Physiology
Volume285
Issue number2 54-2
Publication statusPublished - 2003 Aug 1

Keywords

  • Bone resorbing cycle
  • Membrane depolarization
  • Resorbing and motile activities

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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