Characteristics of restitution kinetics in repolarization of rabbit atrium.
The study was designed to characterize restitution kinetics in atrial repolarization of rabbits and to examine effects of K+ or Ca2+ channel blockers on restitution. Action potentials were recorded from rabbit atrial tissue. Restitution curves of phase I amplitude and action potential duration at 50 and 90% repolarization (APD50, APD90) were defined at a basic cycle length of 0.5 s during control and with interventions. Restitution of phase I amplitude had a monoexponential function with a time constant of 2.8 +/- 0.2 s. The curves of APD50 frequently had a monoexponential function and time constants were 1.8 +/- 0.1 s. Restitution curves of APD90 were biphasic: a descending phase followed by an ascending phase. The blocker of Ito1 (a 4-aminopyridine-sensitive component of the transient outward current), 4-aminopyridine, flattened the restitution curves of phase I amplitude, and APD50 and APD90 curves became monophasic. Sotalol, a selective IKr (a rapid component of the delayed rectifier K+ current) blocker, did not alter curves of phase I amplitude and APD50 but shifted APD90 curves upward. Cadmium, a Ca2+ blocker shifted curves of phase I amplitude and APD50 downward and abolished the ascending phase of APD90 curves. We conclude that kinetics of Ito1 and ICa (calcium current) may account for characteristics of restitution of atrial repolarization in rabbit.
Qi
A
A
Department of Medicine, University of British Columbia, Vancouver, Canada.
Tang
C
C
Yeung-Lai-Wah
J A
JA
Kerr
C R
CR
D000200:Action Potentials; D000818:Animals; D016275:Atrial Function; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007700:Kinetics; D009200:Myocardial Contraction / Q000502:physiology*; D026902:Potassium Channel Blockers; D011817:Rabbits
D002121:Calcium Channel Blockers; D026902:Potassium Channel Blockers