Calcium/calmodulin-dependent protein kinase II regulation of IKs during sustained β-adrenergic receptor stimulation

Background Sustained β-adrenergic receptor (β-AR) stimulation causes pathophysiological changes during heart failure (HF), including inhibition of the slow component of the delayed rectifier potassium current (I Ks ). Aberrant calcium handling, including increased activation of calcium/calmodulin-dependent protein kinase II (CaMKII), contributes to arrhythmia development during HF. Objective The purpose of this study was to investigate CaMKII regulation of KCNQ1 (pore-forming subunit of I Ks ) during sustained β-AR stimulation and associated functional implications on I Ks . Methods KCNQ1 phosphorylation was assessed using liquid chromatography-tandem mass spectrometry after sustained β-AR stimulation with isoproterenol (ISO). Peptide fragments corresponding to KCNQ1 residues were synthesized to identify CaMKII phosphorylation at the identified sites. Dephosphorylated (alanine) and phosphorylated (aspartic acid) mimics were introduced at identified residues. Whole-cell, voltage-clamp experiments were performed in human endothelial kidney 293 cells coexpressing wild-type or mutant KCNQ1 and KCNE1 (auxiliary subunit) during ISO treatment or lentiviral δCaMKII overexpression. Results Novel KCNQ1 carboxy-terminal sites were identified with enhanced phosphorylation during sustained β-AR stimulation at T482 and S484. S484 peptides demonstrated the strongest δCaMKII phosphorylation. Sustained β-AR stimulation reduced I Ks activation ( P = .02 vs control) similar to the phosphorylated mimic ( P = .62 vs sustained β-AR). Individual phosphorylated mimics at S484 ( P  = .04) but not at T482 ( P = .17) reduced I Ks function. Treatment with CN21 (CaMKII inhibitor) reversed the reductions in I Ks vs CN21-Alanine control ( P Ks similar to ISO treatment in wild type ( P P = .99). Conclusion CaMKII regulates KCNQ1 at S484 during sustained β-AR stimulation to inhibit I Ks . The ability of CaMKII to inhibit I Ks may contribute to arrhythmogenicity during HF.