title: Unique uptake and efflux systems of inorganic phosphate in osteoclast-like cells.
abstract: During bone resorption, a large amount of inorganic phosphate (P(i)) is generated within the osteoclast hemivacuole. The mechanisms involved in the disposal of this P(i) are not clear. In the present study, we investigated the efflux of P(i) from osteoclast-like cells. P(i) efflux was activated by acidic conditions in osteoclast-like cells derived by the treatment of RAW264.7 cells with receptor activator of nuclear factor-kappaB ligand. Acid-induced P(i) influx was not observed in renal proximal tubule-like opossum kidney cells, osteoblast-like MC3T3-E1 cells, or untreated RAW264.7 cells. Furthermore, P(i) efflux was stimulated by extracellular P(i) and several P(i) analogs [phosphonoformic acid (PFA), phosphonoacetic acid, arsenate, and pyrophosphate]. P(i) efflux was time dependent, with 50% released into the medium after 10 min. The efflux of P(i) was increased by various inhibitors that block P(i) uptake, and extracellular P(i) did not affect the transport of [(14)C]PFA into the osteoclast-like cells. Preloading of cells with P(i) did not stimulate P(i) efflux by PFA, indicating that the effect of P(i) was not due to transstimulation of P(i) transport. P(i) uptake was also enhanced under acidic conditions. Agents that prevent increases in cytosolic free Ca(2+) concentration, including acetoxymethyl ester of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, 2-aminoethoxydiphenyl borate, and bongkrekic acid, significantly inhibited P(i) uptake in the osteoclast-like cells, suggesting that P(i) uptake is regulated by Ca(2+) signaling in the endoplasmic reticulum and mitochondria of osteoclast-like cells. These results suggest that osteoclast-like cells have a unique P(i) uptake/efflux system and can prevent P(i) accumulation within osteoclast hemivacuoles.
authors.affiliation: Department of Molecular Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Kuramoto-Cho 3-18-15, Tokushima City 770-8503, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Ito
authors.forename: Sakiko
authors.initials: S
authors.lastname: Haito
authors.forename: Mari
authors.initials: M
authors.lastname: Furumoto
authors.forename: Yoko
authors.initials: Y
authors.lastname: Uehata
authors.forename: Aya
authors.initials: A
authors.lastname: Sakurai
authors.forename: Hiroko
authors.initials: H
authors.lastname: Segawa
authors.forename: Sawako
authors.initials: S
authors.lastname: Tatsumi
authors.forename: Masashi
authors.initials: M
authors.lastname: Kuwahata
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Miyamoto
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000378:metabolism; D017245:Foscarnet / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism; D009893:Opossums; D009994:Osmolar Concentration; D010006:Osteoblasts / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D010710:Phosphates / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D053245:RANK Ligand / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D000998:Antiviral Agents; D010710:Phosphates; D053245:RANK Ligand; D017245:Foscarnet; D012964:Sodium; D002118:Calcium