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.285 (2), p.C457-C466

Ort / Verlag

United States

Erscheinungsjahr

2003

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• Department of Physiological Science and Molecular Biology, Fukuoka Dental College, Fukuoka 814-0193, Japan Submitted 21 January 2003 ; accepted in final form 3 April 2003 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 Ca 2 + concentration ([Ca 2 + ] i ) in nonresorbing vs. resorbing rat osteoclasts. Basal [Ca 2 + ] 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 [Ca 2 + ] i , whereas high K + increased [Ca 2 + ] i in resorbing state osteoclasts. In nonresorbing/motile cells, membrane depolarization and hyperpolarization applied by the patch-clamp technique decreased and increased [Ca 2 + ] i , respectively. Removal of extracellular Ca 2 + or application of 300 µM La 3 + reduced [Ca 2 + ] i to 50 nM in nonresorbing/motile osteoclasts, and high-K + -induced reduction of [Ca 2 + ] i could not be observed under these conditions. Neither inhibition of intracellular Ca 2 + stores or plasma membrane Ca 2 + pumps nor blocking of L- and N-type Ca 2 + channels significantly reduced [Ca 2 + ] 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 La 3 + -sensitive Ca 2 + entry pathway is continuously active under resting conditions, keeping [Ca 2 + ] i high. Changes in membrane potential regulate osteoclastic motility by controlling the net amount of Ca 2 + entry in a "reversed" voltage-dependent manner, i.e., depolarization decreases and hyperpolarization increases [Ca 2 + ] i . membrane depolarization; resorbing and motile activities; bone resorbing cycle Address for reprint requests and other correspondence: H. Kajiya, Dept. of Physiological Science and Molecular Biology, Fukuoka Dental College, 2-15-1 Tamura, Sawara-ku, Fukuoka Japan, 814-0193 (E-mail address: kajiya{at}college.fdcnet.ac.jp ).