Atrium-specific Kir3.x determines inducibility, dynamics, and termination of fibrillation by regulating restitution-driven alternans.
BACKGROUND
Atrial fibrillation is the most common cardiac arrhythmia. Ventricular proarrhythmia hinders pharmacological atrial fibrillation treatment. Modulation of atrium-specific Kir3.x channels, which generate a constitutively active current (I(K,ACh-c)) after atrial remodeling, might circumvent this problem. However, it is unknown whether and how I(K,ACh-c) contributes to atrial fibrillation induction, dynamics, and termination. Therefore, we investigated the effects of I(K,ACh-c) blockade and Kir3.x downregulation on atrial fibrillation.


RESULTS
Neonatal rat atrial cardiomyocyte cultures and intact atria were burst paced to induce reentry. To study the effects of Kir3.x on action potential characteristics and propagation patterns, cultures were treated with tertiapin or transduced with lentiviral vectors encoding Kcnj3- or Kcnj5-specific shRNAs. Kir3.1 and Kir3.4 were expressed in atrial but not in ventricular cardiomyocyte cultures. Tertiapin prolonged action potential duration (APD; 54.7±24.0 to 128.8±16.9 milliseconds; P<0.0001) in atrial cultures during reentry, indicating the presence of I(K,ACh-c). Furthermore, tertiapin decreased rotor frequency (14.4±7.4 to 6.6±2.0 Hz; P<0.05) and complexity (6.6±7.7 to 0.6±0.8 phase singularities; P<0.0001). Knockdown of Kcnj3 or Kcnj5 gave similar results. Blockade of I(K,ACh-c) prevented/terminated reentry by prolonging APD and changing APD and conduction velocity restitution slopes, thereby altering the probability of APD alternans and rotor destabilization. Whole-heart mapping experiments confirmed key findings (e.g., >50% reduction in atrial fibrillation inducibility after I(K,ACh-c) blockade).


CONCLUSIONS
Atrium-specific Kir3.x controls the induction, dynamics, and termination of fibrillation by modulating APD and APD/conduction velocity restitution slopes in atrial tissue with I(K,ACh-c). This study provides new molecular and mechanistic insights into atrial tachyarrhythmias and identifies Kir3.x as a promising atrium-specific target for antiarrhythmic strategies.
Laboratory of Experimental Cardiology, Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands (B.O.B., Z.N., S.F.A.A., D.L.Y., M.J.S., A.A.V.d.V., D.A.P.); and Department of Physics and Astronomy, Ghent University, Ghent, Belgium (I.V.K., A.V.P.).
Brian O
BO
Bingen
Zeinab
Z
Neshati
Saïd F A
SF
Askar
Ivan V
IV
Kazbanov
Dirk L
DL
Ypey
Alexander V
AV
Panfilov
Martin J
MJ
Schalij
Antoine A F
AA
de Vries
Daniël A
DA
Pijnappels
D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology*; D001514:Bee Venoms / Q000494:pharmacology; D002478:Cells, Cultured; D004195:Disease Models, Animal; D015536:Down-Regulation / Q000502:physiology*; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria / Q000187:drug effects / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D056969:Voltage-Sensitive Dye Imaging
D001514:Bee Venoms; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C029738:tertiapin; D000109:Acetylcholine
G protein-coupled inwardly rectifying potassium channels; RNA interference; action potentials; arrhythmia; atrial fibrillation; cardiomyocyte; voltage-sensitive dye imaging