title: Signature currents: a patch-clamp method for determining the selectivity of ion-channel blockers in isolated cardiac myocytes.
abstract: BACKGROUND
  We describe a simple method using membrane potential ramps for rapidly determining the ion-channel selectivity of drugs that affect action-potential duration in isolated cardiac myocytes. The method allows the simultaneous assay of compounds on a number of ionic currents in a single cardiac cell.
  
  
  METHODS
  Trains of membrane potential ramps were applied from -90 to +70 mV at 0.33 Hz to obtain a consistent "signature current," in which the major individual currents involved in the cardiac action potential could be easily identified. Confirmatory experiments were performed using known inhibitors of these currents.
  
  
  RESULTS
  The identities of the currents in the signature were established by varying the concentrations of extracellular cations and by adding known ion channel blockers to superfusion solutions. Inhibition of each current had a characteristic and reproducible effect on the overall signature current.
  
  
  CONCLUSIONS
  The consistent current signature in the presence and absence of blockers suggests that this method could be used for tertiary electrophysiological evaluation of compounds, eg, in a drug discovery program focusing on antiarrhythmic agents. The ability to assay for secondary effects of novel compounds against multiple currents in the target cell type is convenient and avoids the artefacts associated with using artificial expression systems.
authors.affiliation: Department of Pharmacology, University of Bristol, Bristol, UK, and the Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: C I
authors.initials: CI
authors.lastname: Spencer
authors.forename: W
authors.initials: W
authors.lastname: Uchida
authors.forename: L
authors.initials: L
authors.lastname: Turner
authors.forename: R Z
authors.initials: RZ
authors.lastname: Kozlowski
mesh_terms: D000200:Action Potentials / Q000187:drug effects* / Q000502:physiology; D000818:Animals; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D007473:Ion Channels / Q000037:antagonists & inhibitors*; D018408:Patch-Clamp Techniques / Q000379:methods; D051381:Rats; D017208:Rats, Wistar
chemical_list: D007473:Ion Channels