Sensitivity of Flecainide Inhibition of hERG Channels to Channel Inactivation

Abstract

hERG K+ channels are sensitive to pharmacological inhibition by many different drugs including Class I and Class III antiarrhythmics. These drugs exhibit differences regarding the reliance of hERG current (IhERG) blockade on channel inactivation: Class Ia (quinidine and disopyramide) and Ic (propafenone) agents are less dependent on inactivation than are Class III methanesulphonanilide compounds (dofetilide and E-4031) (1-3). Flecainide is a Class Ic agent that inhibits IhERG at clinically relevant concentrations (4) and its sensitivity to hERG inactivation has not been systematically investigated. This study was undertaken to evaluate the influence of inactivation on flecainide blockade of hERG, through the use of attenuated-inactivation mutants S631A, N588K and S631A/N588K (3). IhERG was recorded using whole-cell patch-clamp at 37oC from hERG-expressing HEK293 cells. IhERG tails were measured at −40mV after a 2sec depolarizing step from −80mV to +20mV (n≥5 at each concentration). Flecainide produced a concentration-dependent inhibition of wild-type (WT) IhERG with an IC50 of 1.49µM (CI:1.27-1.74). The IC50 for inhibition of S631A-IhERG [7.49µM (CI:6.33-8.87)] was ∼5-fold that for WT-IhERG, whilst that for N588K-IhERG [6.50µM (CI:5.37-7.88)] was ∼4.4-fold that of WT-IhERG. The S631A/N588K double mutant, which leads to a greater attenuation of IhERG inactivation than does either individual mutation (3), exhibited an IC50 [19.16µM (CI:15.43-23.80)] ∼12.9 fold that of WT-IhERG. Comparison of these data with prior work using these inactivation-mutants (3) is suggestive that flecainide inhibition of IhERG depends on inactivation to a slightly greater extent than Class Ia drugs and the Class Ic drug propafenone, but to a much lesser extent than does E-4031.Funded by the British Heart Foundation.1. Ficker et al. Circ Res 1998; 82:386-95.2. Perrin et al. Mol Pharmacol 2008; 74:1443-52.3. McPate et al. BJP 2008; 155:957-966.4. Paul et al. BJP 2002; 136:717-29.