title: Mechanism of loss of Kv11.1 K+ current in mutant T421M-Kv11.1-expressing rat ventricular myocytes: interaction of trafficking and gating.
abstract: BACKGROUND
  Type 2 long QT syndrome involves mutations in the human ether a-go-go-related gene (hERG or KCNH2). T421M, an S1 domain mutation in the Kv11.1 channel protein, was identified in a resuscitated patient. We assessed its biophysical, protein trafficking, and pharmacological mechanisms in adult rat ventricular myocytes.
  
  
  RESULTS
  Isolated adult rat ventricular myocytes were infected with wild-type (WT)-Kv11.1- and T421M-Kv11.1-expressing adenovirus and analyzed with the use of patch clamp, Western blot, and confocal imaging techniques. Expression of WT-Kv11.1 or T421M-Kv11.1 produced peak tail current (I(Kv11.1)) of 8.78±1.18 and 1.91±0.22 pA/pF, respectively. Loss of mutant I(Kv11.1) resulted from (1) a partially trafficking-deficient channel protein with reduced cell surface expression and (2) altered channel gating with a positive shift in the voltage dependence of activation and altered kinetics of activation and deactivation. Coexpression of WT+T421M-Kv11.1 resulted in heterotetrameric channels that remained partially trafficking deficient with only a minimal increase in peak I(Kv11.1) density, whereas the voltage dependence of channel gating became WT-like. In the adult rat ventricular myocyte model, both WT-Kv11.1 and T421M-Kv11.1 channels responded to β-adrenergic stimulation by increasing I(Kv11.1).
  
  
  CONCLUSIONS
  The T421M-Kv11.1 mutation caused a loss of I(Kv11.1) through interactions of abnormal protein trafficking and channel gating. Furthermore, for coexpressed WT+T421M-Kv11.1 channels, different dominant-negative interactions govern protein trafficking and ion channel gating, and these are likely to be reflected in the clinical phenotype. Our results also show that WT and mutant Kv11.1 channels responded to β-adrenergic stimulation.
authors.affiliation: Department of Medicine, University of Wisconsin, Madison,WI 53792, USA.
authors.forename: Sadguna Y
authors.initials: SY
authors.lastname: Balijepalli
authors.forename: Evi
authors.initials: E
authors.lastname: Lim
authors.forename: Sarah P
authors.initials: SP
authors.lastname: Concannon
authors.forename: Chen L
authors.initials: CL
authors.lastname: Chew
authors.forename: Kassandra E
authors.initials: KE
authors.lastname: Holzem
authors.forename: David J
authors.initials: DJ
authors.lastname: Tester
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ackerman
authors.forename: Brian P
authors.initials: BP
authors.lastname: Delisle
authors.forename: Ravi C
authors.initials: RC
authors.lastname: Balijepalli
authors.forename: Craig T
authors.initials: CT
authors.lastname: January
mesh_terms: D000328:Adult; D000818:Animals; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics* / Q000502:physiology*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008133:Long QT Syndrome / Q000235:genetics* / Q000503:physiopathology; D008564:Membrane Potentials / Q000502:physiology; D020125:Mutation, Missense / Q000235:genetics; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000502:physiology; D014162:Transfection / Q000379:methods
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C000606918:Kcnh2 protein, rat; D011943:Receptors, Adrenergic, beta; D011188:Potassium