title: Hypotonic-induced stretching of plasma membrane activates transient receptor potential vanilloid channels and sodium-calcium exchangers in mouse odontoblasts.
abstract: BACKGROUND
  A number of transient receptor potential (TRP) channels have been identified as membrane-bound sensory proteins in odontoblasts. However, the activation properties of these channels remain to be clarified. The purpose of this study was to investigate hypotonic stimulation-induced Ca(2+) entry via TRP vanilloid subfamily member (TRPV) 1, TRPV2, and TRPV4 channels, which are sensitive to osmotic and mechanical stimuli, and their functional coupling with Na(+)-Ca(2+) exchangers (NCXs) in mouse odontoblast lineage cells.
  
  
  METHODS
  We examined TRP channel activity by measuring intracellular-free Ca(2+) concentration by using fura-2 fluorescence and ionic current recordings with whole-cell patch-clamp methods. Protein localization and messenger RNA expression were characterized using immunofluorescence and reverse-transcription polymerase chain reaction analyses.
  
  
  RESULTS
  Extracellular hypotonic solution-induced stretching of plasma membrane resulted in the activation of Ca(2+) influx and inward currents. TRPV1, TRPV2, and TRPV4 channel antagonists inhibited the hypotonic stimulation-induced Ca(2+) entry and currents. Their respective agonists activated Ca(2+) entry. Although the increase in the intracellular free Ca(2+) concentration decayed rapidly after the applications of these TRPV channel agonists, NCX inhibitors significantly prolonged the decay time constant. The messenger RNA expression of TRPV1, TRPV2, and TRPV4 channels; NCX isoforms 2 and 3; and dentin sialophosphoprotein were up-regulated after 24 hours of exposure to the hypotonic culture medium.
  
  
  CONCLUSIONS
  These results indicate that stretching of the odontoblast membrane activates TRPV1-, TRPV2-, and TRPV4-mediated Ca(2+) entry, and increased intracellular-free Ca(2+) concentration is extruded via NCXs. These results suggest that odontoblasts can act as sensors that detect stimuli applied to exposed dentin and drive a number of cellular functions including dentinogenesis and/or sensory transduction.
authors.affiliation: Oral Health Science Center, Tokyo Dental College, Chiba, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Sato
authors.forename: Ubaidus
authors.initials: U
authors.lastname: Sobhan
authors.forename: Maki
authors.initials: M
authors.lastname: Tsumura
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Kuroda
authors.forename: Manabu
authors.initials: M
authors.lastname: Soya
authors.forename: Aya
authors.initials: A
authors.lastname: Masamura
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nishiyama
authors.forename: Akira
authors.initials: A
authors.lastname: Katakura
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ichinohe
authors.forename: Masakazu
authors.initials: M
authors.lastname: Tazaki
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Shibukawa
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D019070:Cell Lineage; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D003470:Culture Media; D003804:Dentin / Q000648:ultrastructure; D016326:Extracellular Matrix Proteins / Q000187:drug effects; D057446:Hydrodynamics; D007038:Hypotonic Solutions; D040542:Mechanotransduction, Cellular / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009804:Odontoblasts / Q000166:cytology* / Q000187:drug effects; D009995:Osmosis / Q000502:physiology; D010750:Phosphoproteins / Q000187:drug effects; D010812:Physical Stimulation; D020033:Protein Isoforms / Q000037:antagonists & inhibitors / Q000502:physiology; D051381:Rats; D012795:Sialoglycoproteins / Q000187:drug effects; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000502:physiology; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000502:physiology*; D000099311:Dentin Sialophosphoprotein
chemical_list: D003470:Culture Media; D016326:Extracellular Matrix Proteins; D007038:Hypotonic Solutions; D010750:Phosphoproteins; D020033:Protein Isoforms; D012795:Sialoglycoproteins; D019831:Sodium-Calcium Exchanger; D050916:TRPV Cation Channels; D000099311:Dentin Sialophosphoprotein; C494482:TRPV1 protein, human; C400769:TRPV2 protein, human; C416986:TRPV4 protein, human