title: Similar arrhythmicity in hypertrophic and fibrotic cardiac cultures caused by distinct substrate-specific mechanisms.
abstract: OBJECTIVE
  Cardiac hypertrophy and fibrosis are associated with potentially lethal arrhythmias. As these substrates often occur simultaneously in one patient, distinguishing between pro-arrhythmic mechanisms is difficult. This hampers understanding of underlying pro-arrhythmic mechanisms and optimal treatment. This study investigates and compares arrhythmogeneity and underlying pro-arrhythmic mechanisms of either cardiac hypertrophy or fibrosis in in vitro models.
  
  
  RESULTS
  Fibrosis was mimicked by free myofibroblast (MFB) proliferation in neonatal rat ventricular monolayers. Cultures with inhibited MFB proliferation were used as control or exposed to phenylephrine to induce hypertrophy. At Day 9, cultures were studied with patch-clamp and optical-mapping techniques and assessed for protein expression. In hypertrophic (n = 111) and fibrotic cultures (n = 107), conduction and repolarization were slowed. Triggered activity was commonly found in these substrates and led to high incidences of spontaneous re-entrant arrhythmias [67.5% hypertrophic, 78.5% fibrotic vs. 2.9% in controls (n = 102)] or focal arrhythmias (39.1, 51.7 vs. 8.8%, respectively). Kv4.3 and Cx43 protein expression levels were decreased in hypertrophy but unaffected in fibrosis. Depolarization of cardiomyocytes (CMCs) was only found in fibrotic cultures (-48 ± 7 vs. -66 ± 7 mV in control, P < 0.001). L-type calcium-channel blockade prevented arrhythmias in hypertrophy, but caused conduction block in fibrosis. Targeting heterocellular coupling by low doses of gap-junction uncouplers prevented arrhythmias by accelerating repolarization only in fibrotic cultures.
  
  
  CONCLUSIONS
  Cultured hypertrophic or fibrotic myocardial tissues generated similar focal and re-entrant arrhythmias. These models revealed electrical remodelling of CMCs as a pro-arrhythmic mechanism of hypertrophy and MFB-induced depolarization of CMCs as a pro-arrhythmic mechanism of fibrosis. These findings provide novel mechanistic insight into substrate-specific arrhythmicity.
authors.affiliation: Laboratory of Experimental Cardiology, Department of Cardiology,  Leiden University Medical Center, 2300 RC Leiden,  The Netherlands.
authors.forename: Saïd F A
authors.initials: SF
authors.lastname: Askar
authors.forename: Brian O
authors.initials: BO
authors.lastname: Bingen
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Schalij
authors.forename: Jim
authors.initials: J
authors.lastname: Swildens
authors.forename: Douwe E
authors.initials: DE
authors.lastname: Atsma
authors.forename: Cindy I
authors.initials: CI
authors.lastname: Schutte
authors.forename: Antoine A F
authors.initials: AA
authors.lastname: de Vries
authors.forename: Katja
authors.initials: K
authors.lastname: Zeppenfeld
authors.forename: Dirk L
authors.initials: DL
authors.lastname: Ypey
authors.forename: Daniël A
authors.initials: DA
authors.lastname: Pijnappels
mesh_terms: D000200:Action Potentials; D000818:Animals; D000831:Animals, Newborn; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D006332:Cardiomegaly / Q000150:complications* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D002478:Cells, Cultured; D018920:Coculture Techniques; D018031:Connexin 43 / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D005355:Fibrosis; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D018408:Patch-Clamp Techniques; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D051672:Shal Potassium Channels / Q000378:metabolism; D056969:Voltage-Sensitive Dye Imaging
chemical_list: D000889:Anti-Arrhythmia Agents; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018031:Connexin 43; C580592:Gja1 protein, rat; D051672:Shal Potassium Channels; D010656:Phenylephrine