Role of chloride currents in repolarizing rabbit atrial myocytes.
Rabbit atrial cells manifest a prominent transient outward K+ current (Ito1), but this current recovers slowly from inactivation and is unlikely to be important at physiological rates (3-5 Hz). Depolarization of rabbit atrial cells also elicits a transient Ca(2+)-dependent outward Cl- current (Ito2). To compare the relative magnitude of these transient outward currents at various rates, we applied whole cell voltage-clamp techniques to isolated rabbit atrial myocytes. Whereas peak Ito1 exceeded Ito2 at slow rates (0.1 Hz), Ito1 was strongly reduced as rate was increased (by 97 +/- 2%, mean +/- SE, at 4 Hz), while Ito2 was slightly reduced (by 28 +/- 4%, 4 Hz). The reversal potential of transient outward tail currents at 0.07 Hz was -49 +/- 9 mV, while at 2.5 Hz the reversal potential became -18 +/- 7 mV (calculated Cl- reversal potential -18 mV). The addition of the Cl- transport blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 150 microM) or the replacement of external Cl- with methanesulfonate inhibited a large part of the transient outward current elicited by depolarization at 4 Hz. DIDS and Cl- replacement increased action potential duration in both single rabbit atrial cells and multicellular rabbit atrial preparations. We conclude that the Ca(2+)-dependent Cl- current is substantially larger than the transient K+ current at physiological rates in the rabbit and is likely to play a more important role in action potential repolarization than the latter current in this tissue in vivo.
Wang
Z
Z
Montreal Heart Institute, Department of Medicine, University of Montreal, Quebec, Canada.
Fermini
B
B
Feng
J
J
Nattel
S
S
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials; D000818:Animals; D002712:Chlorides / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D006339:Heart Rate; D009206:Myocardium / Q000166:cytology; D011817:Rabbits
D002712:Chlorides; D015761:4-Aminopyridine