title: Structure-activity relationship of fenamates as Slo2.1 channel activators.
abstract: Niflumic acid, 2-{[3-(trifluoromethyl)phenyl]amino}pyridine-3-carboxylic acid (NFA), a nonsteroidal anti-inflammatory drug that blocks cyclooxygenase (COX), was shown previously to activate [Na(+)](i)-regulated Slo2.1 channels. In this study, we report that other fenamates, including flufenamic acid, mefenamic acid, tolfenamic acid, meclofenamic acid, and a phenyl acetic acid derivative, diclofenac, also are low-potency (EC(50) = 80 μM to 2.1 mM), partial agonists of human Slo2.1 channels heterologously expressed in Xenopus oocytes. Substituent analysis determined that N-phenylanthranilic acid was the minimal pharmacophore for fenamate activation of Slo2.1 channels. The effects of fenamates were biphasic, with an initial rapid activation phase followed by a slow phase of current inhibition. Ibuprofen, a structurally dissimilar COX inhibitor, did not activate Slo2.1. Preincubation of oocytes with ibuprofen did not significantly alter the effects of NFA, suggesting that neither channel activation nor inhibition is associated with COX activity. A point mutation (A278R) in the pore-lining S6 segment of Slo2.1 increased the sensitivity to activation and reduced the inhibition induced by NFA. Together, our results suggest that fenamates bind to two sites on Slo2.1 channels: an extracellular accessible site to activate and a cytoplasmic accessible site in the pore to inhibit currents.
authors.affiliation: Nora Eccles Harrison Cardiovascular Research and Training Institute, Department of Physiology, University of Utah, Salt Lake City, Utah 84112, USA.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Garg
authors.forename: Michael C
authors.initials: MC
authors.lastname: Sanguinetti
mesh_terms: D000818:Animals; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D005260:Female; D054361:Fenamates / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D007052:Ibuprofen / Q000494:pharmacology; D066298:In Vitro Techniques; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000819:agonists; D009544:Niflumic Acid / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists* / Q000235:genetics; D000081033:Potassium Channels, Sodium-Activated; D013329:Structure-Activity Relationship; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology
chemical_list: D016861:Cyclooxygenase Inhibitors; D054361:Fenamates; C494841:KCNMA1 protein, human; C480494:KCNT2 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000081033:Potassium Channels, Sodium-Activated; D062367:ortho-Aminobenzoates; D009544:Niflumic Acid; C001209:fenamic acid; D007052:Ibuprofen