Abstract
Niflumic acid [2-((3-(trifluoromethyl)phenyl)amino)-3-pyridinecarboxylic acid, NFA] is a nonsteroidal anti-inflammatory drug that also blocks or modulates the gating of a wide spectrum of ion channels. Here we investigated the mechanism of channel activation by NFA on ether-a-go-go-related gene (ERG) K+ channel subtypes expressed in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. NFA acted from the extracellular side of the membrane to differentially enhance ERG channel currents independent of channel state. At 1 mM, NFA shifted the half-point for activation by -6, -18, and -11 mV for ERG1, ERG2, and ERG3 channels, respectively. The half-point for channel inactivation was shifted by +5 to +9 mV by NFA. The structural basis for the ERG subtype-specific response to NFA was explored with chimeric channels and site-directed mutagenesis. The molecular determinants of enhanced sensitivity of ERG2 channels to NFA were isolated to an Arg and a Thr triplet in the extracellular S3-S4 linker.
Footnotes
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This work was supported by National Heart, Lung, and Blood Institute/National Institutes of Health grant HL55236.
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ABBREVIATIONS: NFA, niflumic acid [2-((3-(trifluoromethyl)phenyl)amino)-3-pyridinecarboxylic acid]; NS1643, 1,3-bis(2-hydroxy-5-trifluoromethylphenyl)urea; PD-118057, 2-{4-[2-(3,4-dichloro-phenyl)-ethyl]-phenylamino}-benzoic acid; RPR260243, (3R, 4R)-4-(3-(6-methoxyquinolin-4-yl)-3-oxo-propyl)-1-(3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl)-piperidine-3-carboxylic acid; zERG, zebrafish ERG; rERG, rat ERG; hERG, human ERG; bp, base pair(s); VSD, voltage sensor domain; WT, wild-type; I-V, current-voltage; ERG1, human ether-a-go-go-related gene.
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↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
- Received November 14, 2007.
- Accepted January 22, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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