Regional differences in rabbit atrial repolarization: importance of transient outward current.
Regional differences in rabbit atrial repolarization were investigated using a conventional microelectrode technique. A more rapid phase 1 repolarization (lower phase 1 amplitude) was seen in the left atrial (LA) roof area compared with the right atrial (RA) roof area: 54 +/- 10 vs. 82 +/- 6 mV at 1,000 ms (P < 0.001). In addition, action potential duration at 40 mV above the resting potential (APD40) was shorter in LA and was associated with a slower phase 3 repolarization rate. Furthermore, the recovery time constant of phase 1 amplitude at 500 ms was 0.9 +/- 0.2 s in LA and 3.5 +/- 1.5 s in RA (P < 0.001). Pacing cycle lengths (2,000, 1,500, 1,000, 800, and 500 ms) modulated phase 1 amplitude, APD40, and phase 3 rate in both regions. 4-Aminopyridine (4-AP; 1 mM), a selective transient outward current (I(to)) blocker, abolished cycle length dependence of the above action potential parameters and diminished the differences in electrophysiological properties between the two regions. 4-AP also flattened the restitution curve of phase 1 amplitude in both regions. In conclusion, the findings suggest that the different kinetics of I(to) play an important role in regional differences of atrial repolarization.
Qi
A
A
Department of Medicine, University of British Columbia, Vancouver, Canada.
Yeung-Lai-Wah
J A
JA
Xiao
J
J
Kerr
C R
CR
D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D011817:Rabbits; D013997:Time Factors
D015761:4-Aminopyridine