Fibroblast Inward-Rectifier Potassium Current Upregulation in Profibrillatory Atrial Remodeling
Rationale: Fibroblasts (FBs) are involved in cardiac arrhythmogenesis, and contribute to the atrial fibrillation (AF) substrate in congestive heart failure (CHF) by generating tissue-fibrosis. FBs display robust ion-currents, but their functional importance is poorly understood.
Objective: To characterize atrial FB inward-rectifier K+-current (IK1) remodeling in CHF and its effects on FB properties.
Methods and Results: Freshly-isolated left atrial (LA) FBs were obtained from control and CHF (ventricular tachypacing) dogs. Patch-clamp was used to record resting membrane potential (RMP) and IIK1. RMP was significantly increased by CHF (from -43.2±0.8 mV, control, to -55.5±0.9 mV). CHF upregulated IIK1 (e.g. at -90 mV from -1.1±0.2 pA/pF to -2.7±0.5 pA/pF), and increased expression of KCNJ2 mRNA (by 52%) and protein (by 80%). Ba2+ (300-μmol/L) decreased RMP and suppressed the RMP difference between CTL and CHF. Store operated Ca2+-entry (Fura-2 AM) and FB proliferation (flow cytometry) were enhanced by CHF. Lentivirus-mediated overexpression of KCNJ2 (KCNJ2-OE) enhanced IK1 and hyperpolarized FBs. Functional KCNJ2-suppression by lentiviral-mediated expression of a dominant negative KCNJ2-construct (KCNJ2-DN) suppressed IIK1 and depolarized RMP. KCNJ2-OE increased Ca2+-entry and FB proliferation whereas KCNJ2-DN had opposite effects. Fibroblast-hyperpolarization to mimic CHF-effects on RMP enhanced Ca2+-entry. MicroRNA-26a, which targets KCNJ2, was downregulated in CHF FBs. Knockdown of endogenous microRNA-26 to mimic CHF effects unregulated IIK1.
Conclusions: CHF upregulates fibroblast KCNJ2 expression and currents, thereby hyperpolarizing RMP, increasing Ca2+-entry and enhancing atrial FB proliferation. These effects are likely mediated by microRNA-26a downregulation. Remodeling-induced fibroblast KCNJ2 expression-changes may play a role in AF promoting FB remodeling and structural/arrhythmic consequences.
- Received September 23, 2014.
- Revision received January 16, 2015.
- Accepted January 21, 2015.