title: Acid-inducible proton influx currents in the plasma membrane of murine osteoclast-like cells.
abstract: Acidification of the resorption pits, which is essential for dissolving bone, is produced by secretion of protons through vacuolar H(+)-ATPases in the plasma membrane of bone-resorbing cells, osteoclasts. Consequently, osteoclasts face highly acidic extracellular environments, where the pH gradient across the plasma membrane could generate a force driving protons into the cells. Proton influx mechanisms during the acid exposure are largely unknown, however. In this study, we investigated extracellular-acid-inducible proton influx currents in osteoclast-like cells derived from a macrophage cell line (RAW264). Decreasing extracellular pH to <5.5 induced non-ohmic inward currents. The reversal potentials depended on the pH gradients across the membrane and were independent of concentrations of Na(+), Cl(-), and HCO3 (-), suggesting that they were carried largely by protons. The acid-inducible proton influx currents were not inhibited by amiloride, a widely used blocker for cation channels/transporters, or by 4,4'-diisothiocyanato-2,2'-stilbenesulfonate(DIDS) which blocks anion channels/transporters. Additionally, the currents were not significantly affected by V-ATPase inhibitors, bafilomycin A1 and N,N'-dicyclohexylcarbodiimide. Extracellular Ca(2+) (10 mM) did not affect the currents, but 1 mM ZnCl2 decreased the currents partially. The intracellular pH in the vicinity of the plasma membrane was dropped by the acid-inducible H(+) influx currents, which caused overshoot of the voltage-gated H(+) channels after removal of acids. The H(+) influx currents were smaller in undifferentiated, mononuclear RAW cells and were negligible in COS7 cells. These data suggest that the acid-inducible H(+) influx (H(+) leak) pathway may be an additional mechanism modifying the pH environments of osteoclasts upon exposure to strong acids.
authors: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka, 545-8585, Japan. kunomyk@med.osaka-cu.ac.jp.
authors: Miyuki
authors: M
authors: Kuno
authors: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka, 545-8585, Japan.
authors: Guangshuai
authors: G
authors: Li
authors: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka, 545-8585, Japan.
authors: Yoshie
authors: Y
authors: Moriura
authors: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka, 545-8585, Japan.
authors: Yoshiko
authors: Y
authors: Hino
authors: Central Laboratory, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka, 545-8585, Japan.
authors: Junko
authors: J
authors: Kawawaki
authors: Department of Physiology, Osaka City University Graduate School of Medicine, 1-4-3 Asahimachi, Abeno-ku, Osaka, 545-8585, Japan.
authors: Hiromu
authors: H
authors: Sakai
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D002522:Chlorocebus aethiops; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D010010:Osteoclasts / Q000378:metabolism*; D011522:Protons; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D007473:Ion Channels; D011522:Protons; D017967:Zinc Compounds; C016837:zinc chloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium
keywords: Extracellular acidification; Osteoclast; Proton influx current; Proton leak