title: 9-Phenanthrol inhibits recombinant and arterial myocyte TMEM16A channels.
abstract: OBJECTIVE
  In arterial smooth muscle cells (myocytes), intravascular pressure stimulates membrane depolarization and vasoconstriction (the myogenic response). Ion channels proposed to mediate pressure-induced depolarization include several transient receptor potential (TRP) channels, including TRPM4, and transmembrane protein 16A (TMEM16A), a Ca(2+) -activated Cl(-) channel (CaCC). 9-Phenanthrol, a putative selective TRPM4 channel inhibitor, abolishes myogenic tone in cerebral arteries, suggesting that either TRPM4 is essential for pressure-induced depolarization, upstream of activation of other ion channels or that 9-phenanthrol is non-selective. Here, we tested the hypothesis that 9-phenanthrol is also a TMEM16A channel blocker, an ion channel for which few inhibitors have been identified.
  
  
  METHODS
  Patch clamp electrophysiology was used to measure rat cerebral artery myocyte and human recombinant TMEM16A (rTMEM16A) currents or currents generated by recombinant bestrophin-1, another Ca(2+) -activated Cl(-) channel, expressed in HEK293 cells.
  
  
  RESULTS
  9-Phenanthrol blocked myocyte TMEM16A currents activated by either intracellular Ca(2+) or Eact , a TMEM16A channel activator. In contrast, 9-phenanthrol did not alter recombinant bestrophin-1 currents. 9-Phenanthrol reduced arterial myocyte TMEM16A currents with an IC50 of ∼12 μM. Cell-attached patch recordings indicated that 9-phenanthrol reduced single rTMEM16A channel open probability and mean open time, and increased mean closed time without affecting the amplitude.
  
  
  CONCLUSIONS
  These data identify 9-phenanthrol as a novel TMEM16A channel blocker and provide an explanation for the previous observation that 9-phenanthrol abolishes myogenic tone when both TRPM4 and TMEM16A channels contribute to this response. 9-Phenanthrol may be a promising candidate from which to develop TMEM16A channel-specific inhibitors.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, Memphis, TN, USA.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Burris
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Simon
authors.initials: S
authors.lastname: Bulley
authors.forename: Zachary P
authors.initials: ZP
authors.lastname: Neeb
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Jaggar
mesh_terms: D000818:Animals; D000075369:Anoctamin-1; D001158:Arteries / Q000166:cytology*; D000075002:Bestrophins; D002118:Calcium / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D032342:Muscle Cells / Q000187:drug effects* / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010616:Phenanthrenes / Q000494:pharmacology*; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: C476213:ANO1 protein, human; D000075369:Anoctamin-1; C508904:Best1 protein, rat; D000075002:Bestrophins; D018118:Chloride Channels; D009363:Neoplasm Proteins; D010616:Phenanthrenes; D011994:Recombinant Proteins; C091375:9-phenanthrol; D002118:Calcium