title: Activity-dependent development of P2X7 current and Ca2+ entry in rabbit osteoclasts.
abstract: Bone remodeling is regulated by local factors and modulated by mechanical stimuli. Mechanical stimulation can cause release of ATP, an agent that stimulates osteoclastic resorption at low concentrations and inhibits at high concentrations. We examined whether osteoclasts express P2X(7) receptors, which are activated by high concentrations of ATP and can behave as ion channels or cause the formation of membrane pores. Rabbit osteoclasts were studied using patch clamp techniques. Successive or prolonged applications of 2'- & 3'-O-(4-benzoylbenzoyl)-ATP (BzATP, a relatively potent P2X(7) agonist) or high concentrations of ATP caused the development of a slowly deactivating inward current. The underlying channel was permeable only to small cations, ruling out pore formation. Divalent cations reduced current magnitude, consistent with the presence of P2X(7) receptors, a finding confirmed in rat osteoclasts by immunocytochemistry. Successive applications of BzATP also elicited [Ca(2+)](i) elevations that required extracellular Ca(2+). The BzATP-induced current and the rise of [Ca(2+)](i) were temporally associated, and both were inhibited by PPADS, a P2X(7) antagonist. This study demonstrates that high concentrations of ATP activate P2X(7) receptors and provides the first functional evidence for an extracellular ligand-gated Ca(2+) influx pathway in osteoclasts. ATP released in response to mechanical stimuli may act through P2X(7) receptors to inhibit osteoclastic resorption.
authors.affiliation: Canadian Institutes of Health Research Group in Skeletal Development and Remodeling, Department of Physiology and Division of Oral Biology, Faculty of Medicine and Dentistry, The University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: L N
authors.initials: LN
authors.lastname: Naemsch
authors.forename: S J
authors.initials: SJ
authors.lastname: Dixon
authors.forename: S M
authors.initials: SM
authors.lastname: Sims
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000345:Affinity Labels / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007150:Immunohistochemistry; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D010010:Osteoclasts / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058486:Receptors, Purinergic P2X7; D013050:Spectrometry, Fluorescence; D013997:Time Factors
chemical_list: D000345:Affinity Labels; D002412:Cations; D007473:Ion Channels; D008024:Ligands; C546470:P2rx7 protein, rat; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D002118:Calcium