title: ZFHX3 knockdown increases arrhythmogenesis and dysregulates calcium homeostasis in HL-1 atrial myocytes.
abstract: BACKGROUND
  ZFHX3 plays an important role in the genesis of atrial fibrillation. However, the atrial electrophysiological effects of ZFHX3 are not clear. This study sought to investigate roles of ZFHX3 in atrial electrophysiology and calcium homeostasis by using HL-1 atrial myocytes knocked-down with ZFHX3.
  
  
  METHODS
  Patch clamp, confocal fluorescence microscopy and Western blot were used to study electrical activity, ionic currents, calcium homeostasis and protein expressions in stable ZFHX3 shRNA cells.
  
  
  RESULTS
  As compared to control, ZFHX3 shRNA cells with 28% decline of ZFHX3 protein had a larger sarcoplasmic reticulum Ca(2+) content by 62%, Ca(2+) transient by 20%, and calcium leak by 75%. ZFHX3 shRNA cells (n=35) had shorter action potential duration (APD) at 50% (14.7 ± 0.9 versus 20.3 ± 1.4 ms, P<0.005), and 20% (6.1 ± 0.3 versus 8.3 ± 0.8 ms, P<0.005) repolarization than control cells (n=30). ZFHX3 shRNA cells (n=10) had larger amplitudes of isoproterenol (1 μM)-induced delayed after depolarization (14.1 ± 0.9 versus 7.2 ± 0.2 mV, P<0.05) than control cells (n=10). Besides, acetylcholine (3 μM) shortened APD at 90% repolarization to a greater extent (19 ± 4% versus 7 ± 2%, P<0.01) in ZFHX3 shRNA cells (n=11) than in control cells (n=12). In addition, ZFHX3 shRNA cells had increased expressions of SERCA2a, ryanodine receptor, Kv1.4, Kv1.5 and Kir3.4. Moreover, ZFHX3 shRNA cells had a larger SERCA2a activity, ultra-rapid delayed rectifier potassium currents, transient outward currents and acetylcholine-sensitive potassium currents.
  
  
  CONCLUSIONS
  ZFHX3 knock-down in atrial myocytes dysregulated calcium homeostasis and increased atrial arrhythmogenesis, which may contribute to the occurrence of AF.
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan; Department of Medical Education and Research, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan.
authors.forename: Yu-Hsun
authors.initials: YH
authors.lastname: Kao
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Jung-Chieh
authors.initials: JC
authors.lastname: Hsu
authors.affiliation: Department of Biomedical Engineering, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Yao-Chang
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan.
authors.forename: Yung-Kuo
authors.initials: YK
authors.lastname: Lin
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Baigalmaa
authors.initials: B
authors.lastname: Lkhagva
authors.affiliation: School of Medicine, National Yang-Ming University, Taipei, Taiwan; Division of Cardiology and Cardiovascular Research Center, Taipei Veterans General Hospital, Taipei, Taiwan.
authors.forename: Shih-Ann
authors.initials: SA
authors.lastname: Chen
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan; Division of Cardiovascular Medicine, Department of Internal Medicine, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan. Electronic address: a9900112@ms15.hinet.net.
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Chen
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D055785:Gene Knockdown Techniques; D006325:Heart Atria / Q000166:cytology / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology*; D051379:Mice; D032383:Myocytes, Cardiac / Q000502:physiology*
chemical_list: D018398:Homeodomain Proteins; C489511:Zfhx3 protein, mouse; D002118:Calcium
keywords: Atrial arrhythmogenesis; Calcium homeostasis; ZFHX3