title: Identification and characterization of a transient outward K+ current in human induced pluripotent stem cell-derived cardiomyocytes.
abstract: BACKGROUND
  The ability to recapitulate mature adult phenotypes is critical to the development of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) as models of disease. The present study examines the characteristics of the transient outward current (Ito) and its contribution to the hiPSC-CM action potential (AP).
  
  
  METHODS
  Embryoid bodies were made from a hiPS cell line reprogrammed with Oct4, Nanog, Lin28 and Sox2. Sharp microelectrodes were used to record APs from beating-clusters (BC) and patch-clamp techniques were used to record Ito in single hiPSC-CM. mRNA levels of Kv1.4, KChIP2 and Kv4.3 were quantified from BCs.
  
  
  RESULTS
  BCs exhibited spontaneous beating (60.5±2.6 bpm) and maximum-diastolic-potential (MDP) of 67.8±0.8 mV (n=155). A small 4-aminopyridine-sensitive phase-1-repolarization was observed in only 6/155 BCs. A robust Ito was recorded in the majority of cells (13.7±1.9 pA/pF at +40 mV; n=14). Recovery of Ito from inactivation (at -80 mV) showed slow kinetics (τ1=200±110 ms (12%) and τ2=2380±240 ms (80%)) accounting for its minimal contribution to the AP. Transcript data revealed relatively high expression of Kv1.4 and low expression of KChIP2 compared to human native ventricular tissues. Mathematical modeling predicted that restoration of IK1 to normal levels would result in a more negative MDP and a prominent phase-1-repolarization.
  
  
  CONCLUSIONS
  The slow recovery kinetics of Ito coupled with a depolarized MDP account for the lack of an AP notch in the majority of hiPSC-CM. These characteristics reveal a deficiency for the development of in vitro models of inherited cardiac arrhythmia syndromes in which Ito-induced AP notch is central to the disease phenotype.
authors.affiliation: Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY 13501, USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Cordeiro
authors.forename: Vladislav V
authors.initials: VV
authors.lastname: Nesterenko
authors.forename: Serge
authors.initials: S
authors.lastname: Sicouri
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Goodrow
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Treat
authors.forename: Mayurika
authors.initials: M
authors.lastname: Desai
authors.forename: Yuesheng
authors.initials: Y
authors.lastname: Wu
authors.forename: Michael Xavier
authors.initials: MX
authors.lastname: Doss
authors.forename: Charles
authors.initials: C
authors.lastname: Antzelevitch
authors.forename: José M
authors.initials: JM
authors.lastname: Di Diego
mesh_terms: D002460:Cell Line; D006801:Humans; D057026:Induced Pluripotent Stem Cells / Q000166:cytology / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D051605:Kv Channel-Interacting Proteins / Q000378:metabolism; D051665:Kv1.4 Potassium Channel / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051672:Shal Potassium Channels / Q000378:metabolism
chemical_list: C496752:KCNIP2 protein, human; D051605:Kv Channel-Interacting Proteins; D051665:Kv1.4 Potassium Channel; D051672:Shal Potassium Channels; D011188:Potassium
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