Trigger-Specific Remodeling of KCa2 Potassium Channels in Models of Atrial Fibrillation

Ann-Kathrin Rahm,1– 3 Dominik Gramlich,1– 3 Teresa Wieder,1,2 Mara Elena Müller,1– 3 Axel Schoeffel,1,2 Fadwa A El Tahry,1 Patrick Most,1,2 Tanja Heimberger,1,3 Steffi Sandke,1,3 Tanja Weis,1,3 Nina D Ullrich,4 Thomas Korff,4,5 Patrick Lugenbiel,1– 3 Hugo A Katus,1– 3 Dierk Thomas1– 3 1Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, 69120, Germany; 2HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Heidelberg, 69120, Germany; 3DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, 69120, Germany; 4Institute of Physiology and Pathophysiology, Department of Cardiovascular Physiology, Heidelberg University, Heidelberg, 69120, Germany; 5European Center for Angioscience (ECAS), Medical Faculty Mannheim, Heidelberg University, Mannheim, 68167, GermanyCorrespondence: Dierk ThomasDepartment of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, Heidelberg, 69120, GermanyTel +49 6221 568855Fax +49 6221 565514Email dierk.thomas@med.uni-heidelberg.deAim: Effective antiarrhythmic treatment of atrial fibrillation (AF) constitutes a major challenge, in particular, when concomitant heart failure (HF) is present. HF-associated atrial arrhythmogenesis is distinctly characterized by prolonged atrial refractoriness. Small-conductance, calcium-activated K+ (KCa, SK, KCNN) channels contribute to cardiac action potential repolarization and are implicated in AF susceptibility and therapy. The mechanistic impact of AF/HF-related triggers on atrial KCa channels is not known. We hypothesized that tachycardia, stretch, β-adrenergic stimulation, and hypoxia differentially determine KCa 2.1– 2.3 channel remodeling in atrial cells.Methods: KCNN1-3 transcript levels were assessed in AF/HF patients and in a pig model of atrial tachypacing-induced AF with reduced left ventricular function. HL-1 atrial myocytes were subjected to proarrhythmic triggers to investigate the effects on Kcnn mRNA and KCa channel protein.Results: Atrial KCNN1-3 expression was reduced in AF/HF patients. KCNN2 and KCNN3 suppression was recapitulated in the corresponding pig model. In contrast to human AF, KCNN1 remained unchanged in pigs. Channel- and stressor-specific remodeling was revealed in vitro. Lower expression levels of KCNN1/KCa 2.1 were linked to stretch and β-adrenergic stimulation. Furthermore, KCNN3/KCa 2.3 expression was suppressed upon tachypacing and hypoxia. Finally, KCNN2/KCa 2.2 abundance was specifically enhanced by hypoxia.Conclusion: Reduction of KCa 2.1– 2.3 channel expression might contribute to the action potential prolongation in AF complicated by HF. Subtype-specific KCa 2 channel remodeling induced by tachypacing, stretch, β-adrenergic stimulation, or hypoxia is expected to differentially determine atrial remodeling, depending on patient-specific activation of each triggering factor. Stressor-dependent KCa 2 regulation in atrial myocytes provides a starting point for mechanism-based antiarrhythmic therapy.Keywords: atrial fibrillation, calcium, KCa channel, KCNN, remodeling, SK channel