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


CONCLUSIONS
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.
Li
Gui-Rong
GR
Institute of Cardiovascular Science and Medicine/Department of Medicine, The University of Hong Kong, Hong Kong SAR, China. grli@hkucc.hku.hk
Du
Xin-Ling
XL
Siow
Yaw L
YL
O
Karmin
K
Tse
Hung-Fat
HF
Lau
Chu-Pak
CP
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000032:analysis / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D012433:Ryanodine / Q000494:pharmacology; D051672:Shal Potassium Channels; D013552:Swine
D002121:Calcium Channel Blockers; D018118:Chloride Channels; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051672:Shal Potassium Channels; D002104:Cadmium; D012433:Ryanodine; D015761:4-Aminopyridine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium