The Interaction of Caveolin 3 Protein with the Potassium Inward Rectifier Channel Kir2.1: PHYSIOLOGY AND PATHOLOGY RELATED TO LONG QT SYNDROME 9 (LQT9)* |
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Authors: | Ravi Vaidyanathan Amanda L. Vega Chunhua Song Qing Zhou Bihua Tan Stuart Berger Jonathan C. Makielski Lee L. Eckhardt |
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Affiliation: | From the ‡Department of Medicine, Division of Cardiovascular Medicine and the Cellular and Molecular Arrhythmia Research Program,University of Wisconsin, Madison, Wisconsin 53792 and ;the §Medical College of Wisconsin, Milwaukee, Wisconsin 53226 |
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Abstract: | Mutations in CAV3 cause LQT syndrome 9 (LQT9). A previously reported LQT9 patient had prominent U waves on ECG, a feature that has been correlated with Kir2.1 loss of function. Our objective was to determine whether caveolin 3 (Cav3) associates with Kir2.1 and whether LQT9-associated CAV3 mutations affect the biophysical properties of Kir2.1. Kir2.1 current (IK1) density was measured using the whole-cell voltage clamp technique. WT-Cav3 did not affect IK1. However, F97C-Cav3 and T78M-Cav3 decreased IK1 density significantly by ∼60%, and P104L-Cav3 decreased IK1 density significantly by ∼30% at −60 mV. Immunostained rat heart cryosections and HEK293 cells cotransfected with Kir2.1 and WT-Cav3 both demonstrated colocalization of Kir2.1 and WT-Cav3 by confocal imaging. Cav3 coimmunoprecipitated with Kir2.1 in human ventricular myocytes and in heterologous expression systems. Additionally, FRET efficiency was highly specific, with a molecular distance of 5.6 ± 0.4 nm, indicating close protein location. Colocalization experiments found that Cav3 and Kir2.1 accumulated in the Golgi compartment. On-cell Western blot analysis showed decreased Kir2.1 cell surface expression by 60% when expressed with F97C-Cav3 and by 20% when expressed with P104L-Cav3 compared with WT-Cav3. This is the first report of an association between Cav3 and Kir2.1. The Cav3 mutations F97C-Cav3, P104L-Cav3, and T78M-Cav3 decreased IK1 density significantly. This effect was related to a reduced cell surface expression of Kir2.1. Kir2.1 loss of function is additive to the increase described previously in late INa, prolonging repolarization and leading to arrhythmia generation in Cav3-mediated LQT9. |
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Keywords: | Cardiomyopathy Caveolin Electrophysiology Ion Channels Potassium Channels Long QT Syndrome (LQTS) Arrhythmias Basic Studies |
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