Affiliation:
1. Department of Medicine, University of Chicago, IL 60637.
Abstract
Early afterdepolarizations (EADs) are a type of triggered activity found in heart muscle. We used voltage-clamped sheep cardiac Purkinje fibers to examine the mechanism underlying EADs induced near action potential plateau voltages with the Ca2+ current agonist Bay K 8644 and the effect of several interventions known to suppress or enhance these EADs. Bay K 8644 produced an inward shift of the steady-state current-voltage relation near plateau voltages. Tetrodotoxin, lidocaine, verapamil, nitrendipine, and raising [K]o abolish EADs and shift the steady-state current-voltage relations outwardly. Using a two-pulse voltage-clamp protocol, an inward current transient was present at voltages where EADs were induced. The voltage-dependence of availability of the inward current transient and of EAD induction were similar. The time-dependence of recovery from inactivation of the inward current transient and of EAD amplitude were nearly identical. Without recovery of the inward current transient, EADs could not be elicited. The inward current transient was enhanced with Bay K 8644 and blocked by nitrendipine, but was not abolished by tetrodotoxin or replacement of [Na]o with an impermeant cation. These results support a hypothesis that the induction of EADs near action potential plateau voltages requires 1) a conditioning phase controlled by the sum of membrane currents present near the action potential plateau and characterized by lengthening and flattening of the plateau within a voltage range where, 2) recovery from inactivation and reactivation of L-type Ca2+ channels to carry the depolarizing charge can occur. Our results suggest an essential role for the L-type Ca2+ "window" current and provide a framework for understanding the role of several membrane currents in the induction and block of EADs.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Reference51 articles.
1. Cranefield PF: The Conduction of the Cardiac Impulse. New York Future Publishing Co 1975
2. Effects of pacing on triggered activity induced by early afterdepolarizations.
3. Coulombe A Coraboeuf E Malecot C Deroubaix E: Role of the "Na window" current and other ionic currents in triggering early afterdepolarization and resulting re-excitation in Purkinje fibers in Zipes DP Jalife J (eds): Cardiac Electrophysiology and Arrhythmias. Orlando Fla Grune and Stratton 1985 pp 43-49
Cited by
652 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献