Jie Wu1, Nobu Naiki2, Wei-Guang Ding3, Seiko Ohno2, Koichi Kato2, Wei-Jin Zang4, Brian P Delisle5, Hiroshi Matsuura3, Minoru Horie6. 1. Department of Pharmacology, Medical School of Xi'an Jiaotong University, Xi'an, China; Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan; Department of Physiology, Shiga University of Medical Science, Otsu, Japan. 2. Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan. 3. Department of Physiology, Shiga University of Medical Science, Otsu, Japan. 4. Department of Pharmacology, Medical School of Xi'an Jiaotong University, Xi'an, China. 5. Department of Physiology, University of Kentucky, Lexington, Kentucky. 6. Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan. Electronic address: horie@belle.shiga-med.ac.jp.
Abstract
OBJECTIVES: This study sought to explore molecular mechanisms underlying the adrenergic-induced QT prolongation associated with KCNQ1 mutations. BACKGROUND: The most frequent type of congenital long QT syndrome is LQT1, which is caused by mutations in the gene (KCNQ1) that encodes the alpha subunit of the slow component of delayed rectifier K(+) current (IKs) channel. We identified 11 patients from 4 unrelated families that are heterozygous for KCNQ1-G269S. Most patients remained asymptomatic, and their resting corrected QT intervals ranged from normal to borderline but were prolonged significantly during exercise. METHODS: Wild-type (WT) KCNQ1 and/or KCNQ1-G269S (G269S) were expressed in mammalian cells with KCNE1. IKs-like currents were measured in control conditions or after isoproterenol or protein kinase A (PKA) stimulation using the patch-clamp technique. Additionally, experiments that incorporated the phosphomimetic KCNQ1 substitution, S27D, in WT or KCNQ1-G269S were also performed. RESULTS: The coexpression of WT-KCNQ1 with varying amounts of G269S decreased IKs, shifted the current-voltage I-V relation of IKs to more positive potentials, and accelerated the IKs deactivation rates in a concentration-dependent manner. In addition, the coexpression of G269S and WT blunted the activation of IKs in response to isoproterenol or PKA stimulation. Lastly, a phosphomimetic substitution in G269S did not show an increased IKs. CONCLUSIONS: G269S modestly affected IKs in control conditions, but it almost completely blunted IKs responsiveness in conditions that simulate or mimic PKA phosphorylation of KCNQ1. This insensitivity to PKA stimulation may explain why patients with G269S mutation showed an excessive prolongation of QT intervals on exercise.
OBJECTIVES: This study sought to explore molecular mechanisms underlying the adrenergic-induced QT prolongation associated with KCNQ1 mutations. BACKGROUND: The most frequent type of congenital long QT syndrome is LQT1, which is caused by mutations in the gene (KCNQ1) that encodes the alpha subunit of the slow component of delayed rectifier K(+) current (IKs) channel. We identified 11 patients from 4 unrelated families that are heterozygous for KCNQ1-G269S. Most patients remained asymptomatic, and their resting corrected QT intervals ranged from normal to borderline but were prolonged significantly during exercise. METHODS: Wild-type (WT) KCNQ1 and/or KCNQ1-G269S (G269S) were expressed in mammalian cells with KCNE1. IKs-like currents were measured in control conditions or after isoproterenol or protein kinase A (PKA) stimulation using the patch-clamp technique. Additionally, experiments that incorporated the phosphomimetic KCNQ1 substitution, S27D, in WT or KCNQ1-G269S were also performed. RESULTS: The coexpression of WT-KCNQ1 with varying amounts of G269S decreased IKs, shifted the current-voltage I-V relation of IKs to more positive potentials, and accelerated the IKs deactivation rates in a concentration-dependent manner. In addition, the coexpression of G269S and WT blunted the activation of IKs in response to isoproterenol or PKA stimulation. Lastly, a phosphomimetic substitution in G269S did not show an increased IKs. CONCLUSIONS:G269S modestly affected IKs in control conditions, but it almost completely blunted IKs responsiveness in conditions that simulate or mimic PKA phosphorylation of KCNQ1. This insensitivity to PKA stimulation may explain why patients with G269S mutation showed an excessive prolongation of QT intervals on exercise.
Authors: Daniel C Bartos; John R Giudicessi; David J Tester; Michael J Ackerman; Seiko Ohno; Minoru Horie; Michael H Gollob; Don E Burgess; Brian P Delisle Journal: Heart Rhythm Date: 2013-11-21 Impact factor: 6.343