Wnt Signaling Selectively Inhibits Sodium Channels in Cardiac Myocytes

Abstract

Background: Wnt signaling plays crucial roles in heart development but is normally suppressed postnatally. In arrhythmogenic conditions, such as cardiac hypertrophy and heart failure, Wnt signaling is reactivated. We explored the potential role of Wnt signaling in arrhythmogenic electrical remodeling by examining ion channel changes in postnatal cardiomyocytes with activated Wnt signaling.Methods: Neonatal rat ventricular myocytes (NRVMs) were treated with either recombinant Wnt3a protein (0.1-1.0 μg/ml) or CHIR-99021 (CH, 3 μM, a glycogen synthase kinase-3β inhibitor) to activate canonical Wnt signaling. Gene expression was assayed by real-time RT-PCR. Western blot and immunocytostaining were used to investigate protein changes. Ionic currents were recorded using whole-cell patch-clamp.Results: Treatment of NRVMs with either Wnt3a or CH caused a dose-dependent increase in Wnt target gene expression (Axin2 and Lef1), indicating activation of the Wnt/β-catenin pathway. Cardiac Na+ current (INa) density was reduced (p 10) by Wnt3a (−20±4 vs. control −59±7 pA/pF, at −30 mV) or CH (−22±5 pA/pF), without changes in steady-state inactivation or repriming kinetics. Wnt3a and CH also produced dose-dependent reductions in the mRNA level of Scn5a (the cardiac Na+ channel α subunit gene), as well as a 60% reduction in Nav1.5 protein level. Consistent with INa reduction, action potentials in Wnt3a-treated NRVMs had lower (p<0.01, n=5) upstroke amplitude (91±3 vs. control 137±2 mV) and decreased maximum upstroke velocity (70±10 vs. control 163±15 V/s). In contrast, inward rectifier K+ current and L-type Ca2+ current were not affected by Wnt3a treatment (n=8).Conclusions: The Wnt/β-catenin pathway selectively suppresses INa expression in postnatal cardiomyocytes and may contribute to arrhythmogenic remodeling in heart failure. Thus, the Wnt/β-catenin pathway may be a novel therapeutic target for heart failure and cardiac arrhythmias.