title: Selective activation of heteromeric SK channels contributes to action potential repolarization in mouse atrial myocytes.
abstract: BACKGROUND
  Activation of small conductance calcium-activated potassium (SK) channels is proposed to contribute to repolarization of the action potential in atrial myocytes. This role is controversial, as these cardiac SK channels appear to exhibit an uncharacteristic pharmacology.
  
  
  OBJECTIVE
  The objectives of this study were to resolve whether activation of SK channels contributes to atrial action potential repolarization and to determine the likely subunit composition of the channel.
  
  
  METHODS
  The effect of 2 SK channel inhibitors was assessed on outward current evoked in voltage clamp and on action potential duration in perforated patch and whole-cell current clamp recording from acutely isolated mouse atrial myocytes. The presence of SK channel subunits was assessed using immunocytochemistry.
  
  
  RESULTS
  A significant component of outward current was reduced by the SK channel blockers apamin and UCL1684. Block by apamin displayed a sensitivity indicating that this current was carried by homomeric SK2 channels. Action potential duration was significantly prolonged by UCL1684, but not by apamin. This effect was accompanied by an increase in beat-to-beat variability and action potential triangulation. This pharmacology was matched by that of expressed heteromeric SK2-SK3 channels in HEK293 cells. Immunocytochemistry showed that atrial myocytes express both SK2 and SK3 channels with an overlapping expression pattern.
  
  
  CONCLUSIONS
  Only proposed heteromeric SK2-SK3 channels are physiologically activated to contribute to action potential repolarization, which is indicated by the difference in pharmacology of evoked outward current and prolongation of atrial action potential duration. The effect of blocking this channel on the action potential suggests that SK channel inhibition during cardiac function has the potential to be proarrhythmic.
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Hancock
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors.forename: Kate L
authors.initials: KL
authors.lastname: Weatherall
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors.forename: Stéphanie C
authors.initials: SC
authors.lastname: Choisy
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors.forename: Andrew F
authors.initials: AF
authors.lastname: James
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.
authors.forename: Jules C
authors.initials: JC
authors.lastname: Hancox
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom. Electronic address: N.V.Marrion@bris.ac.uk.
authors.forename: Neil V
authors.initials: NV
authors.lastname: Marrion
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D057809:HEK293 Cells; D006325:Heart Atria / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D051379:Mice; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*
chemical_list: D026902:Potassium Channel Blockers; D051640:Small-Conductance Calcium-Activated Potassium Channels; D001030:Apamin
keywords: Action potential duration; Atrial action potential; Repolarization; SK channels