title: Investigations of the Navβ1b sodium channel subunit in human ventricle; functional characterization of the H162P Brugada syndrome mutant.
abstract: Brugada syndrome (BrS) is a rare inherited disease that can give rise to ventricular arrhythmia and ultimately sudden cardiac death. Numerous loss-of-function mutations in the cardiac sodium channel Nav1.5 have been associated with BrS. However, few mutations in the auxiliary Navβ1-4 subunits have been linked to this disease. Here we investigated differences in expression and function between Navβ1 and Navβ1b and whether the H162P/Navβ1b mutation found in a BrS patient is likely to be the underlying cause of disease. The impact of Navβ subunits was investigated by patch-clamp electrophysiology, and the obtained in vitro values were used for subsequent in silico modeling. We found that Navβ1b transcripts were expressed at higher levels than Navβ1 transcripts in the human heart. Navβ1 and Navβ1b coexpressed with Nav1.5 induced a negative shift on steady state of activation and inactivation compared with Nav1.5 alone. Furthermore, Navβ1b was found to increase the current level when coexpressed with Nav1.5, Navβ1b/H162P mutated subunit peak current density was reduced by 48% (-645 ± 151 vs. -334 ± 71 pA/pF), V1/2 steady-state inactivation shifted by -6.7 mV (-70.3 ± 1.5 vs. -77.0 ± 2.8 mV), and time-dependent recovery from inactivation slowed by >50% compared with coexpression with Navβ1b wild type. Computer simulations revealed that these electrophysiological changes resulted in a reduction in both action potential amplitude and maximum upstroke velocity. The experimental data thereby indicate that Navβ1b/H162P results in reduced sodium channel activity functionally affecting the ventricular action potential. This result is an important replication to support the notion that BrS can be linked to the function of Navβ1b and is associated with loss-of-function of the cardiac sodium channel.
authors.affiliation: Danish National Research Foundation Centre for Cardiac Arrhythmia (DARC), Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark;
authors.forename: Lei
authors.initials: L
authors.lastname: Yuan
authors.forename: Jussi T
authors.initials: JT
authors.lastname: Koivumäki
authors.forename: Bo
authors.initials: B
authors.lastname: Liang
authors.forename: Lasse G
authors.initials: LG
authors.lastname: Lorentzen
authors.forename: Chuyi
authors.initials: C
authors.lastname: Tang
authors.forename: Martin N
authors.initials: MN
authors.lastname: Andersen
authors.forename: Jesper H
authors.initials: JH
authors.lastname: Svendsen
authors.forename: Jacob
authors.initials: J
authors.lastname: Tfelt-Hansen
authors.forename: Molly
authors.initials: M
authors.lastname: Maleckar
authors.forename: Nicole
authors.initials: N
authors.lastname: Schmitt
authors.forename: Morten S
authors.initials: MS
authors.lastname: Olesen
authors.forename: Thomas
authors.initials: T
authors.lastname: Jespersen
mesh_terms: D000200:Action Potentials; D000818:Animals; D053840:Brugada Syndrome / Q000235:genetics*; D016466:CHO Cells; D003412:Cricetulus; D004594:Electrophysiology; D020022:Genetic Predisposition to Disease; D006352:Heart Ventricles / Q000737:chemistry* / Q000503:physiopathology; D006801:Humans; D009154:Mutation; D062554:NAV1.5 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000032:analysis; D015222:Sodium Channels / Q000378:metabolism; D014162:Transfection; D062547:Voltage-Gated Sodium Channel beta-1 Subunit / Q000235:genetics* / Q000378:metabolism*
chemical_list: D062554:NAV1.5 Voltage-Gated Sodium Channel; D020033:Protein Isoforms; D012333:RNA, Messenger; C470379:SCN1B protein, human; C568320:SCN5A protein, human; D015222:Sodium Channels; D062547:Voltage-Gated Sodium Channel beta-1 Subunit
keywords: Brugada syndrome; computer simulation; electrophysiology; sodium current; ventricular arrhythmia