Kv1.3 Channel Blockade Improves Inflammatory Profile, Reduces Cardiac Electrical Remodeling, and Prevents Arrhythmia in Type 2 Diabetic Rats.

PURPOSE: Kv1.3 channel regulates the activity of lymphocytes, macrophages, or adipose tissue and its blockade reduces inflammatory cytokine secretion and improves insulin sensitivity in animals with metabolic syndrome and in genetically obese mice. Thus, Kv1.3 blockade could be a strategy for the treatment of type 2 diabetes. Elevated circulating levels of TNFα and IL-1b mediate the higher susceptibility to cardiac arrhythmia in type 2 diabetic rats. We hypothesized that Kv1.3 channel blockade with the psoralen PAP1 could have immunomodulatory properties that prevent QTc prolongation and reduce the risk of arrhythmia in type 2 diabetic rats. METHODS: Type 2 diabetes was induced to Sprague-Dawley rats by high-fat diet and streptozotocin injection. Diabetic animals were untreated, treated with metformin, or treated with PAP1 for 4 weeks. Plasma glucose, insulin, cholesterol, triglycerides, and cytokine levels were measured using commercial kits. ECG were recorded weekly, and an arrhythmia-inducing protocol was performed at the end of the experimental period. Action potentials were recorded in isolated ventricular cardiomyocytes. RESULTS: In diabetic animals, PAP1 normalized glycaemia, insulin resistance, adiposity, and lipid profile. In addition, PAP1 prevented the diabetes-induced repolarization defects through reducing the secretion of the inflammatory cytokines IL-10, IL-12p70, GM-CSF, IFNγ, and TNFα. Moreover, compared to diabetic untreated and metformin-treated animals, those treated with PAP1 had the lowest risk of developing the life-threatening arrhythmia Torsade de Pointes under cardiac challenge. CONCLUSION: Kv1.3 inhibition improves diabetes and diabetes-associated low-grade inflammation and cardiac electrical remodeling, resulting in more protection against cardiac arrhythmia compared to metformin.

CaMKII Modulates the Cardiac Transient Outward K+ Current through its Association with Kv4 Channels in Non-Caveolar Membrane Rafts.

BACKGROUND/AIMS: To test whether the physiological regulation of the cardiac Kv4 channels by the Ca2+/calmodulin-dependent protein kinase II (CaMKII) is restricted to lipid rafts and whether the interactions observed in rat cardiomyocytes also occur in the human ventricle. METHODS: Ventricular myocytes were freshly isolated from Sprague-Dawley rats. Ito was recorded by the whole-cell Patch-Clamp technique. Membrane rafts were isolated by centrifugation in a discontinuous sucrose density gradient. The presence of the proteins of interest was analysed by western blot. Immunogold staining and electron microscopy of heart vibrosections was performed to localize Kv4.2/Kv4.3 and CaMKII proteins. Protein-protein interactions were determined by co-immunoprecipitation experiments in rat and human ventricular mycoytes. RESULTS: Patch-Clamp recordings in control conditions and after lipid raft or caveolae disruption show that the CaMKII-Kv4 channel complex must associate in non-caveolar lipid rafts to be functional. Separation in density gradients, co-immunoprecipitation and electron microscopy show that there are two Kv4 channel populations: one located in caveolae, that is CaMKII independent, and another one located in planar membrane rafts, which is bound to CaMKII. CONCLUSION: CaMKII regulates only the Kv4 channel population located in non-caveolar lipid rafts. Thus, the regulation of cardiac Kv4 channels in rat and human ventricle depends on their subcellular localization.

High Thyrotropin Is Critical for Cardiac Electrical Remodeling and Arrhythmia Vulnerability in Hypothyroidism.

Background: Hypothyroidism, the most common endocrine disease, induces cardiac electrical remodeling that creates a substrate for ventricular arrhythmias. Recent studies report that high thyrotropin (TSH) levels are related to cardiac electrical abnormalities and increased mortality rates. The aim of the present work was to investigate the direct effects of TSH on the heart and its possible causative role in the increased incidence of arrhythmia in hypothyroidism. Methods: A new rat model of central hypothyroidism (low TSH levels) was created and characterized together with the classical propylthiouracil-induced primary hypothyroidism model (high TSH levels). Electrocardiograms were recorded in vivo, and ionic currents were recorded from isolated ventricular myocytes in vitro by the patch-clamp technique. Protein and mRNA were measured by Western blot and quantitative reverse transcription polymerase chain reaction in rat and human cardiac myocytes. Adult human action potentials were simulated in silico to incorporate the experimentally observed changes. Results: Both primary and central hypothyroidism models increased the L-type Ca2+ current (ICa-L) and decreased the ultra-rapid delayed rectifier K+ current (IKur) densities. However, only primary but not central hypothyroidism showed electrocardiographic repolarization abnormalities and increased ventricular arrhythmia incidence during caffeine/dobutamine challenge. These changes were paralleled by a decrease in the density of the transient outward K+ current (Ito) in cardiomyocytes from animals with primary but not central hypothyroidism. In vitro treatment with TSH for 24 hours enhanced isoproterenol-induced spontaneous activity in control ventricular cells and diminished Ito density in cardiomyocytes from control and central but not primary hypothyroidism animals. In human myocytes, TSH decreased the expression of KCND3 and KCNQ1, Ito, and the delayed rectifier K+ current (IKs) encoding proteins in a protein kinase A-dependent way. Transposing the changes produced by hypothyroidism and TSH to a computer model of human ventricular action potential resulted in enhanced occurrence of early afterdepolarizations and arrhythmia mostly in primary hypothyroidism, especially under ß-adrenergic stimulation. Conclusions: The results suggest that suppression of repolarizing K+ currents by TSH underlies most of the electrical remodeling observed in hypothyroidism. This work demonstrates that the activation of the TSH-receptor/protein kinase A pathway in the heart is responsible for the cardiac electrical remodeling and arrhythmia generation seen in hypothyroidism.