Abstract 11351: Potential Role of Fibroblast IK1 Remodeling in the Atrial Fibrillation Substrate
Background: Fibroblasts (FBs) are the most numerous cells in mammalian hearts. They play important roles in arrhythmogenesis by secreting extracellular matrix proteins (fibrosis) and by coupling-effects on cardiomyocyte bioelectricity. This study characterized atrial FB IK1 remodeling in congestive heart failure (CHF) and its role in controlling FB proliferation.
Methods: Freshly isolated left atrial (LA) FBs were obtained from control (CTL) and CHF (2 wk ventricular tachypacing 240 bpm) dogs. Perforated and tight-seal patch clamp were used to record FB resting membrane potential (RMP) and IK1. IK1 was modified by lentivirus-based gene-transfer of wild type-overexpressing (OE Kir2.1) or dominant negative (DN Kir2.1 AAA) subunits.
Results: LA FBs had membrane capacitances of 16.7±0.1 (n=75) and 28.5±1.9 (n=41, P<0.001) pF in CTL and CHF, respectively. RMP averaged -45±1.4 mV in CTL (n=23) and -53±1.6 mV in CHF FBs (n=47, P<0.01). Clear Ba2+-sensitive (300 μ M) inwardly rectifying K+ (Kir) current was recorded and was upregulated in CHF (Fig. A). CHF significantly upregulated Kir2.1 mRNA (by 52%) and protein (by 40%) expression. Ba2+ decreased RMP and eliminated the RMP difference between CTL and CHF (Fig. B), suggesting it is due to IK1. CHF significantly enhanced store-operated Ca2+ entry (Fig. C) and atrial FB proliferation (Fig. D). OE Kir 2.1 greatly enhanced IK1 (Fig. E) and hyperpolarized RMP (Fig. F); DN Kir2.1 AAA eliminated IK1 and depolarized RMP. OE Kir2.1 increased Ca2+ entry (Fig. G) and FB proliferation (Fig. H) whereas DN Kir2.1 AAA had opposite effects.
Conclusions: CHF upregulates fibroblast Kir2.1 expression and currents, hyperpolarizing RMP, increasing Ca2+ entry and cell proliferation. Direct IK1-mediated effects are demonstrated by forced overexpression and downregulation. Remodeling-induced fibroblast Kir2.1 expression changes may play a role in AF-promoting fibroblast remodeling and structural/arrhythmic consequences.
- © 2012 by American Heart Association, Inc.