Chronic PKC Activation Inhibits the Repolarizing Cardiac Current by Decreasing the Functional ion Channel Expression at the Plasma Membrane

Abstract

Background: Cardiac arrhythmias are particularly common in heart failure patients. The slow delayed rectifier K+ current (IKs) is decreased in patients and in animal models of heart failure. However, the molecular mechanisms for IKs decrease are not known. PKC signaling is one of the most prominent pathways activated during heart failure, with both expression and activation of PKC being increased. Hypothesis: Chronic PKC activation inhibits IKs and delays cardiac repolarization, contributing to arrhythmogenic risk in heart failure. Methods: Human IKs channels, PKCalpha catalytic subunit (CA) and alpha1A-adrenoceptor (alpha1A-AR) were expressed in HEK293T cells. IKs current was measured by patch clamp. Subcellular localization of GFP-tagged IKs channels was observed by confocal microscopy. Results: IKs currents were strongly inhibited by either overexpression of PKCalphaCA or 2-hr alpha1A-AR stimulation by phenylephirne (Fig. 1A), although acute application of Ca2+-dependent PKC (cPKC) activator peptide or alpha1A-AR stimulation increased IKs. Plasma membrane localization of GFP-tagged IKs channels was significantly decreased by chronic alpha1A-AR-cPKC signaling activation (Fig.1B). Application of PKC inhibitors or mutation of a putative PKC phosphorylation site in the auxiliary KCNE1 subunit abolished this effect. Conclusion: Chronic PKC activation inhibits IKs currents by decreasing channel plasma membrane expression via direct phosphorylation of KCNE1 subunit. Our results suggest that cPKC-dependent phosphorylation of the IKs channel may contribute to QT prolongation and arrhythmogenesis in heart failure and implicate cPKC inhibitors as potential novel antiarrhythmic drugs.