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This Article Full Text Full Text (PDF) All Versions of this Article: 288/4/C921    most recent 00412.2004v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (5) Citing Articles via Google Scholar Google Scholar Articles by Ito, M. Articles by Miyamoto, K.-i. Search for Related Content PubMed PubMed Citation Articles by Ito, M. Articles by Miyamoto, K.-i.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Characterization of inorganic phosphate transport in osteoclast-like cells

¹Department of Molecular Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima City, Japan; and ²Department of Biochemistry, University of Wisconsin–Madison, Madison, Wisconsin

Submitted 23 August 2004 ; accepted in final form 14 December 2004

Osteoclasts possess inorganic phosphate (P_i) transport systems to take up external P_i during bone resorption. In the present study, we characterized P_i transport in mouse osteoclast-like cells that were obtained by differentiation of macrophage RAW264.7 cells with receptor activator of NF-B ligand (RANKL). In undifferentiated RAW264.7 cells, P_i transport into the cells was Na⁺ dependent, but after treatment with RANKL, Na⁺-independent P_i transport was significantly increased. In addition, compared with neutral pH, the activity of the Na⁺-independent P_i transport system in the osteoclast-like cells was markedly enhanced at pH 5.5. The Na⁺-independent system consisted of two components with K_m of 0.35 mM and 7.5 mM. The inhibitors of P_i transport, phosphonoformic acid, and arsenate substantially decreased P_i transport. The proton ionophores nigericin and carbonyl cyanide p-trifluoromethoxyphenylhydrazone as well as a K⁺ ionophore, valinomycin, significantly suppressed P_i transport activity. Analysis of BCECF fluorescence indicated that P_i transport in osteoclast-like cells is coupled to a proton transport system. In addition, elevation of extracellular K⁺ ion stimulated P_i transport, suggesting that membrane voltage is involved in the regulation of P_i transport activity. Finally, bone particles significantly increased Na⁺-independent P_i transport activity in osteoclast-like cells. Thus, osteoclast-like cells have a P_i transport system with characteristics that are different from those of other Na⁺-dependent P_i transporters. We conclude that stimulation of P_i transport at acidic pH is necessary for bone resorption or for production of the large amounts of energy necessary for acidification of the extracellular environment.

Na⁺-dependent phosphate cotransporter; RAW264.7; phosphate uptake

This article has been cited by other articles:

				M. Ito, S. Haito, M. Furumoto, Y. Uehata, A. Sakurai, H. Segawa, S. Tatsumi, M. Kuwahata, and K.-i. Miyamoto Unique uptake and efflux systems of inorganic phosphate in osteoclast-like cells Am J Physiol Cell Physiol, January 1, 2007; 292(1): C526 - C534. [Abstract] [Full Text] [PDF]