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 (EC50 = 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.
Footnotes
This work was supported by the National Institutes of Health National Heart Lung and Blood Institute [Grant R01HL103877]; and the Nora Eccles Treadwell Foundation.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- IKNa
- intracellular Na+-activated potassium current
- COX
- cyclooxygenase
- cRNA
- complementary RNA
- DFS
- diclofenac sodium, 2-[2-(2,6-dichloroanilino)phenyl]acetic acid
- FFA
- flufenamic acid, 2-[3-(trifluoromethyl)anilino]benzoic acid
- IBP
- ibuprofen
- ISlo2.1
- Slo2.1 current
- MCFA
- meclofenamic acid, 2-[(2,6-dichloro-3-methylphenyl)amino]benzoic acid
- MFA
- mefenamic acid, 2-(2,3-dimethylanilino)benzoic acid
- NFA
- niflumic acid, 2-{[3-(trifluoromethyl)phenyl]amino}pyridine-3-carboxylic acid
- nH
- Hill coefficient
- NSAID
- nonsteroidal anti-inflammatory drug
- PAA
- N-phenylanthranilic acid
- Slo1
- large-conductance Ca2+-activated K+
- TFA
- tolfenamic acid, 2-[(3-chloro-2-methylphenyl)amino]benzoic acid
- WT
- wild-type.
- Received April 9, 2012.
- Accepted July 31, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|