Details

Autor(en) / Beteiligte

• KAJIYA, Hiroshi
• OKAMOTO, Fujio
• FUKUSHIMA, Hidefumi
• TAKADA, Keisuke
• OKABE, Koji

Titel

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

Ist Teil von

• American Journal of Physiology: Cell Physiology, 2003-08, Vol.54 (2), p.C457-C466

Ort / Verlag

Bethesda, MD: American Physiological Society

Erscheinungsjahr

2003

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• 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 mu M La3+ reduced [Ca2+]i 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. [PUBLICATION ABSTRACT]