title: Dual Mechanism for Inhibition of Inwardly Rectifying Kir2.x Channels by Quinidine Involving Direct Pore Block and PIP2-interference.
abstract: Class IA antiarrhythmic drug quinidine was one of the first clinically used compounds to terminate atrial fibrillation and acts as multichannel inhibitor with well-documented inhibitory effects on several cardiac potassium channels. In the mammalian heart, heteromeric assembly of Kir2.1-2.3 channels underlies IK1current. Although a low-affinity block of quinidine on Kir2.1 has already been described, a comparative analysis of effects on other Kir2.x channels has not been performed to date. Therefore, we analyzed the effects of quinidine on wild-type and mutant Kir2.x channels in theXenopusoocyte expression system. Quinidine exerted differential inhibitory effects on Kir2.x channels with the highest affinity toward Kir2.3 subunits. Onset of block was slow and solely reversible in Kir2.2 subunits. Quinidine inhibited Kir2.x currents in a voltage-independent manner. By means of comparative Ala-scanning mutagenesis, we further found that residues E224, F254, D259, and E299 are essential for quinidine block in Kir2.1 subunits. Analogously, quinidine mediated Kir2.3 inhibition by binding corresponding residues E216, D247, D251, and E291. In contrast, Kir2.2 current block merely involved corresponding residue D260. Using channel mutants with altered (phosphatidylinositol 4,5-bisphosphate PIP2) affinities, we were able to demonstrate that high PIP2affinities (i.e., Kir2.3 I214L) correlate with low quinidine sensitivity. Inversely, mutant channels interacting only weakly with PIP2(i.e., Kir2.1 K182Q, and L221I) are prone to a higher inhibitory effect. Thus, we conclude that inhibition of Kir2.x channels by quinidine is mediated by joint modes of action involving direct cytoplasmic pore block and an impaired channel stabilization via interference with PIP2.
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.) christoph.koepple@gmail.com.
authors.forename: Christoph
authors.initials: C
authors.lastname: Koepple
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Daniel
authors.initials: D
authors.lastname: Scherer
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Claudia
authors.initials: C
authors.lastname: Seyler
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Eberhard
authors.initials: E
authors.lastname: Scholz
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Dierk
authors.initials: D
authors.lastname: Thomas
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
authors.affiliation: Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.).
authors.forename: Edgar
authors.initials: E
authors.lastname: Zitron
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001665:Binding Sites / Q000502:physiology; D001702:Biopharmaceutics / Q000379:methods; D009865:Oocytes / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors / Q000378:metabolism; D011802:Quinidine / Q000494:pharmacology*; D014981:Xenopus
chemical_list: D000889:Anti-Arrhythmia Agents; C489461:Kir2.1 channel; C489463:Kir2.2 channel; D019269:Phosphatidylinositol 4,5-Diphosphate; D024661:Potassium Channels, Inwardly Rectifying; D011802:Quinidine