title: Limited role of Ca2+-activated Cl-current in early afterdepolarisations.
abstract: OBJECTIVE
  The proarrhythmic, early afterdepolarisations during phase two of the action potential (phase-2 EADs) are associated with secondary Ca2+release from the sarcoplasmic reticulum. This makes it probable that the Ca2+-activated Cl-current (ICl(Ca)) may contribute to phase-2 EADs. Activation of ICl(Ca)during phase two of the action potential will result in a repolarising current and may thus be expected to prevent excessive depolarisation of phase-2 EADs. The present study was designed to test this hypothesis.
  
  
  METHODS
  The contribution of ICl(Ca)during phase-2 EADs was studied in enzymatically isolated sheep ventricular myocytes using the patch-clamp methodology. EADs were induced at a stimulus frequency of 0.5 Hz by exposure of the myocytes to 1 μM noradrenaline.
  
  
  RESULTS
  The ICl(Ca)blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS, 0.5 mM) abolished phase-1 repolarisation of the action potential in all myocytes tested. This indicates that ICl(Ca)is present in all myocytes. However, DIDS had no effect on phase-2 EAD characteristics.
  
  
  CONCLUSIONS
  In sheep ventricular myocytes, ICl(Ca)contributes to phase-1 repolarisation of the action potential, but plays a limited role in phase-2 EADs.
authors.forename: A O
authors.initials: AO
authors.lastname: Verkerk
authors.forename: H L
authors.initials: HL
authors.lastname: Tan
authors.forename: T
authors.initials: T
authors.lastname: Baartscheer
authors.forename: J H
authors.initials: JH
authors.lastname: Ravesloot
keywords: Ca2+-activated Cl- current; arrhythmias; patch-clamp technique; triggered activity