Calcium-activated transient outward chloride current and phase 1 repolarization of swine ventricular action potential

Cardiovasc Res. 2003 Apr 1;58(1):89-98. doi: 10.1016/s0008-6363(02)00859-3.


Objective: It is unknown whether 4-aminopyridine- (4-AP-) sensitive transient outward K(+) current (I(to1)) and/or Ca(2+)-activated transient outward Cl(-) current (I(Ca.Cl) or I(to2)) contribute(s) to phase 1 repolarization of pig ventricular action potential (AP). The purpose of the present study was to determine ionic contribution of the phase 1 repolarization of AP in pig ventricle.

Methods: We used whole-cell patch techniques to record APs and membrane currents, and Western immunoblotting analysis to detect expression of I(to1) protein (Kv4.2 or Kv4.3) in pig ventricular myocytes.

Results: A transient outward current (I(to)) was activated upon depolarization voltage steps to between -10 and +60 mV from -50 mV in pig ventricular cells, and the I(to) was resistant to 4-AP application, but sensitive to the inhibition by ryanodine (10 micromol/l) and the Ca(2+) channel blockade, and the Cl(-) channel blocker 4,4'-diisothiocyanostilben-2,2'disulfonic acid (DIDS, 150 micromol/l). The current was diminished by external Cl(-) (Cl(-)(o)) replacement and showed a 'bell-shaped' I-V relationship at room temperature, typical of I(to2). No difference in I(to2) was observed in the regional cells from epicardium, midmyocardium, and endocardium of left ventricle. APs showed significant phase 1 and 'spike and dome' in pig ventricular myocytes. The phase 1 and 'spike and dome' of APs were not affected by 4-AP (3 mmol/l), but abolished by replacing Cl(-)(o) and by application of 100 micromol/l DIDS, suggesting I(to2) contribution. Western immunoblotting analysis showed no evidence for the expression of 4-AP-sensitive I(to1) channel protein (Kv4.2 or Kv4.3) in pig ventricular cells.

Conclusion: The results indicate that 4-AP-sensitive I(to1) is not expressed, and only Ca(2+)-activated I(to2) is present in pig cardiac cells, which contributes importantly to the phase 1 repolarization of ventricular APs in this species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / pharmacology
  • 4-Aminopyridine / pharmacology
  • Action Potentials / drug effects
  • Action Potentials / physiology*
  • Animals
  • Blotting, Western / methods
  • Cadmium / pharmacology
  • Calcium / metabolism*
  • Calcium Channel Blockers / pharmacology
  • Chloride Channels / drug effects
  • Chloride Channels / metabolism*
  • Heart Ventricles
  • Myocytes, Cardiac / drug effects
  • Myocytes, Cardiac / metabolism*
  • Patch-Clamp Techniques
  • Potassium Channel Blockers / pharmacology
  • Potassium Channels / analysis
  • Potassium Channels / metabolism
  • Potassium Channels, Voltage-Gated*
  • Ryanodine / pharmacology
  • Shal Potassium Channels
  • Swine


  • Calcium Channel Blockers
  • Chloride Channels
  • Potassium Channel Blockers
  • Potassium Channels
  • Potassium Channels, Voltage-Gated
  • Shal Potassium Channels
  • Cadmium
  • Ryanodine
  • 4-Aminopyridine
  • 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid
  • Calcium