TY - JOUR T1 - The <em>I</em><sub><em>Ks</em></sub> Ion Channel Activator Mefenamic Acid Requires KCNE1 and Modulates Channel Gating in a Subunit-Dependent Manner JF - Molecular Pharmacology JO - Mol Pharmacol SP - 132 LP - 144 DO - 10.1124/mol.119.117952 VL - 97 IS - 2 AU - Yundi Wang AU - Jodene Eldstrom AU - David Fedida Y1 - 2020/02/01 UR - http://molpharm.aspetjournals.org/content/97/2/132.abstract N2 - The pairing of KCNQ1 and KCNE1 subunits together mediates the cardiac slow delayed rectifier current (IKs), which is partly responsible for cardiomyocyte repolarization and physiologic shortening of the cardiac action potential. Mefenamic acid, a nonsteroidal anti-inflammatory drug, has been identified as an IKs activator. Here, we provide a biophysical and pharmacological characterization of mefenamic acid’s effect on IKs. Using whole-cell patch clamp, we show that mefenamic acid enhances IKs activity in both a dose- and stoichiometry-dependent fashion by changing the slowly activating and deactivating IKs current into an almost linear current with instantaneous onset and slowed tail current decay, sensitive to the IKs blocker (3R,4S)-(+)-N-[3-hydroxy-2,2-dimethyl-6-(4,4,4-trifluorobutoxy) chroman-4-yl]-N-methylmethanesulfonamide (HMR1556). Both single channels, which reveal no change in the maximum conductance, and whole-cell studies, which reveal a dramatically altered conductance-voltage relationship despite increasingly longer interpulse intervals, suggest mefenamic acid decreases the voltage sensitivity of the IKs channel and shifts channel gating kinetics toward more negative potentials. Modeling studies revealed that changes in voltage sensor activation kinetics are sufficient to reproduce the dose and frequency dependence of mefenamic acid action on IKs channels. Mutational analysis showed that mefenamic acid’s effect on IKs required residue K41 and potentially other surrounding residues on the extracellular surface of KCNE1, and explains why the KCNQ1 channel alone is insensitive to up to 1 mM mefenamic acid. Given that mefenamic acid can enhance all IKs channel complexes containing different ratios of KCNQ1 to KCNE1, it may provide a promising therapeutic approach to treating life-threatening cardiac arrhythmia syndromes.SIGNIFICANCE STATEMENT The channels which generate the cardiac slow delayed rectifier K+ current (IKs) are composed of KCNQ1 and KCNE1 subunits. Due to the critical role played by IKs in heartbeat regulation, enhancing IKs current has been identified as a promising therapeutic strategy to treat various heart rhythm diseases. Most IKs activators, unfortunately, only work on KCNQ1 alone and not the physiologically relevant IKs channel. We have demonstrated that mefenamic acid can enhance IKs in a dose- and stoichiometry-dependent fashion, regulated by its interactions with KCNE1. ER -