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Attenuated β-adrenergic response in calcium/calmodulin-dependent protein kinase IV-knockout mice.

ABSTRACT: In the present study, we examined the importance of Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) in the regulation of cardiac function using genetically modified CaMKIV-null mice. RT-PCR analysis revealed decreased expression of voltage-dependent calcium channels in the cardiac myocytes of CaMKIV-null mice compared with wild-type mice. CaMKIV-null mice showed shortened QT time on electrocardiograms. Pharmacological analysis revealed decreased responsiveness to the β-adrenergic blocker propranolol in CaMKIV-null mice, whereas the plasma norepinephrine level was not affected. CaMKIV-null mice showed decreased baroreflex on electrocardiograms. Heart rate variability analysis showed unstable R-R intervals, a decreased low frequency power/high frequency power (LF/HF) ratio, and increased standard deviation of the normal to normal R-R intervals (SDNN) in CaMKIV-null mice, suggesting decreased responsiveness to β-adrenergic stimulation in CaMKIV-null mice. Atrial contraction analysis and cardiac action potential recording showed a decreased response to the β-adrenoceptor agonist isoproterenol in CaMKIV-null mice. Furthermore, fluorescence imaging in a CRE-hrGFP assay revealed a decreased response to isoproterenol in CaMKIV-null cardiac myocytes. Taken together, our data strongly suggest a significant effect of CaMKIV gene ablation on cardiac β-adrenergic signal transduction.

SUBMITTER: Murakami M

PROVIDER: S-EPMC8049319 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Sustained ?-adrenergic receptor (?-AR) stimulation causes pathophysiological changes during heart failure (HF), including inhibition of the slow component of the delayed rectifier potassium current (IKs). 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 IKs) during sustained ?-AR stimulation and associated functional implications on IKs. METHODS:KCNQ1 phosphorylation was assessed using liquid chromatography-tandem mass spectrometry after sustained ?-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 ?CaMKII overexpression. RESULTS:Novel KCNQ1 carboxy-terminal sites were identified with enhanced phosphorylation during sustained ?-AR stimulation at T482 and S484. S484 peptides demonstrated the strongest ?CaMKII phosphorylation. Sustained ?-AR stimulation reduced IKs activation (P = .02 vs control) similar to the phosphorylated mimic (P = .62 vs sustained ?-AR). Individual phosphorylated mimics at S484 (P = .04) but not at T482 (P = .17) reduced IKs function. Treatment with CN21 (CaMKII inhibitor) reversed the reductions in IKs vs CN21-Alanine control (P < .01). ?CaMKII overexpression reduced IKs similar to ISO treatment in wild type (P < .01) but not in the dephosphorylated S484 mimic (P = .99). CONCLUSION:CaMKII regulates KCNQ1 at S484 during sustained ?-AR stimulation to inhibit IKs. The ability of CaMKII to inhibit IKs may contribute to arrhythmogenicity during HF.

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Attenuated β-adrenergic response in calcium/calmodulin-dependent protein kinase IV-knockout mice.

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