title: Fenamates as TRP channel blockers: mefenamic acid selectively blocks TRPM3.
abstract: OBJECTIVE
  Fenamates are N-phenyl-substituted anthranilic acid derivatives clinically used as non-steroid anti-inflammatory drugs in pain treatment. Reports describing fenamates as tools to interfere with cellular volume regulation attracted our attention based on our interest in the role of the volume-modulated transient receptor potential (TRP) channels TRPM3 and TRPV4.
  
  
  METHODS
  Firstly, we measured the blocking potencies and selectivities of fenamates on TRPM3 and TRPV4 as well as TRPC6 and TRPM2 by Ca(2+) imaging in the heterologous HEK293 cell system. Secondly, we further investigated the effects of mefenamic acid on cytosolic Ca(2+) and on the membrane voltage in single HEK293 cells that exogenously express TRPM3. Thirdly, in insulin-secreting INS-1E cells, which endogenously express TRPM3, we validated the effect of mefenamic acid on cytosolic Ca(2+) and insulin secretion.
  
  
  RESULTS
  We identified and characterized mefenamic acid as a selective and potent TRPM3 blocker, whereas other fenamate structures non-selectively blocked TRPM3, TRPV4, TRPC6 and TRPM2.
  
  
  CONCLUSIONS
  This study reveals that mefenamic acid selectively inhibits TRPM3-mediated calcium entry. This selectivity was further confirmed using insulin-secreting cells. K(ATP) channel-dependent increases in cytosolic Ca(2+) and insulin secretion were not blocked by mefenamic acid, but the selective stimulation of TRPM3-dependent Ca(2+) entry and insulin secretion induced by pregnenolone sulphate were inhibited. However, the physiological regulator of TRPM3 in insulin-secreting cells remains to be elucidated, as well as the conditions under which the inhibition of TRPM3 can impair pancreatic β-cell function. Our results strongly suggest mefenamic acid is the most selective fenamate to interfere with TRPM3 function.
authors.affiliation: Department of Pharmacology and Experimental Therapy, Institute of Experimental and Clinical Pharmacology and Toxicology, Interfaculty Center of Pharmacogenomics and Pharmaceutical Research (ICePhA), Eberhard-Karls-University, Tübingen, Germany.
authors.forename: Chihab
authors.initials: C
authors.lastname: Klose
authors.forename: Isabelle
authors.initials: I
authors.lastname: Straub
authors.forename: Marc
authors.initials: M
authors.lastname: Riehle
authors.forename: Felicia
authors.initials: F
authors.lastname: Ranta
authors.forename: Dietmar
authors.initials: D
authors.lastname: Krautwurst
authors.forename: Susanne
authors.initials: S
authors.lastname: Ullrich
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Meyerhof
authors.forename: Christian
authors.initials: C
authors.lastname: Harteneck
mesh_terms: D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D054361:Fenamates / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism; D008528:Mefenamic Acid / Q000494:pharmacology*; D051379:Mice; D050052:TRPC Cation Channels / Q000037:antagonists & inhibitors*; D050053:TRPM Cation Channels / Q000037:antagonists & inhibitors; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D054361:Fenamates; D007328:Insulin; D050052:TRPC Cation Channels; D050053:TRPM Cation Channels; C475667:TRPM3 protein, human; D050916:TRPV Cation Channels; C416986:TRPV4 protein, human; D008528:Mefenamic Acid; D002118:Calcium