title: Riluzole activates TRPC5 channels independently of PLC activity.
abstract: OBJECTIVE
  The transient receptor potential channel C5 (TRPC5) is a Ca(2+)-permeable cation channel, which is predominantly expressed in the brain. TRPC5 is activated in a PLC-dependent manner by, as yet, unidentified endogenous messengers. Recently, modulators of TRPC5, like Ca(2+), pH and phospholipids, have been identified. However, the role of TRPC5 in vivo is only poorly understood. Novel specific modulators of TRPC5 might help to elucidate its function.
  
  
  METHODS
  Novel modulators of TRPC5 were identified in a compound screening of approved drugs and natural compounds. The potency and selectivity of TRPC5-activating compounds were determined by fluorometric calcium imaging. The biophysical properties of channel activation by these compounds were analysed using electrophysiological measurements.
  
  
  RESULTS
  Riluzole was identified as a novel activator of TRPC5 (EC₅₀ 9.2 ± 0.5 μM) and its mechanism of action was shown to be independent of G protein signalling and PLC activity. Riluzole-induced TRPC5 currents were potentiated by La(3+) and, utilizing TRPC5 mutants that lack La(3+) binding sites, it was confirmed that riluzole and La(3+) activate TRPC5 by different mechanisms. Recordings of excised inside-out patches revealed a relatively direct effect of riluzole on TRPC5.
  
  
  CONCLUSIONS
  Riluzole can activate TRPC5 heterologously expressed in HEK293 cells as well as those endogenously expressed in the U-87 glioblastoma cell line. Riluzole does not activate any other member of the TRPC family and could, therefore, despite its action on other ion channels, be a useful pharmacological tool for identifying TRPC5-specific currents in immortalized cell lines or in acutely isolated primary cells.
authors.affiliation: Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Leipzig, Germany.
authors.forename: Julia M
authors.initials: JM
authors.lastname: Richter
authors.forename: Michael
authors.initials: M
authors.lastname: Schaefer
authors.forename: Kerstin
authors.initials: K
authors.lastname: Hill
mesh_terms: D000818:Animals; D001665:Binding Sites; D020013:Calcium Signaling / Q000187:drug effects; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D007811:Lanthanum / Q000378:metabolism; D008564:Membrane Potentials; D051379:Mice; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D008969:Molecular Sequence Data; D009154:Mutation; D034622:RNA Interference; D019782:Riluzole / Q000494:pharmacology*; D050052:TRPC Cation Channels / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D050052:TRPC Cation Channels; C491780:TRPC5 protein, human; C112021:Trpc5 protein, mouse; D007811:Lanthanum; D019782:Riluzole; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins
keywords: TRPC5; calcium imaging; patch clamp electrophysiology; riluzole