title: hERG 1b is critical for human cardiac repolarization.
abstract: The human ether-à-go-go-related gene (hERG; or KCNH2) encodes the voltage-gated potassium channel underlying IKr, a repolarizing current in the heart. Mutations in KCNH2 or pharmacological agents that reduce IKr slow action potential (AP) repolarization and can trigger cardiac arrhythmias associated with long QT syndrome. Two channel-forming subunits encoded by KCNH2 (hERG 1a and 1b) are expressed in cardiac tissue. In heterologous expression systems, these subunits avidly coassemble and exhibit biophysical and pharmacological properties distinct from those of homomeric hERG 1a channels. Despite these findings, adoption of hERG 1a/1b heteromeric channels as a model for cardiac IKr has been hampered by the lack of evidence for a direct functional role for the 1b subunit in native tissue. In this study, we measured IKr and APs at physiological temperature in cardiomyocytes derived from human induced pluripotent stem cells (iPSC-CMs). We found that specific knockdown of the 1b subunit using shRNA caused reductions in 1b mRNA, 1b protein levels, and IKr magnitude by roughly one-half. AP duration was increased and AP variability was enhanced relative to controls. Early afterdepolarizations, considered cellular substrates for arrhythmia, were also observed in cells with reduced 1b expression. Similar behavior was elicited when channels were effectively converted from heteromers to 1a homomers by expressing a fragment corresponding to the 1a-specific N-terminal Per-Arnt-Sim domain, which is omitted from hERG 1b by alternate transcription. These findings establish that hERG 1b is critical for normal repolarization and that loss of 1b is proarrhythmic in human cardiac cells.
authors.affiliation: Departments of Neuroscience and.
authors.forename: David K
authors.initials: DK
authors.lastname: Jones
authors.affiliation: Departments of Neuroscience and.
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.affiliation: Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705; and.
authors.forename: Ravi
authors.initials: R
authors.lastname: Vaidyanathan
authors.affiliation: Medicine, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705; and.
authors.forename: L Lee
authors.initials: LL
authors.lastname: Eckhardt
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Trudeau
authors.affiliation: Departments of Neuroscience and garobert@wisc.edu.
authors.forename: Gail A
authors.initials: GA
authors.lastname: Robertson
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000704:Analysis of Variance; D016764:Cell Polarity / Q000502:physiology; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D007150:Immunohistochemistry; D008564:Membrane Potentials / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D016276:Ventricular Function / Q000502:physiology*
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D034741:RNA, Small Interfering
keywords: KCNH2; arrhythmia; early afterdepolarization; hERG; long QT syndrome