Affiliation:
1. Department of Pharmacology, Faculty of Medicine, Kyoto University, Kyoto, Japan
Abstract
Membrane potentials were recorded from a region of the left atrium close to the interatrial septum and from an atrial appendage. Pacemaker activity was induced after exposure to Ba
2+
. The magnitude of the resting potential and of the overshoot decreased with increasing [Ba
2+
]o, whereas duration of the action potential and rise time increased with increasing [Ba
2+
]o. Electrical stimulation for 5 sec at 1/sec to left atria showing automaticity produced bradycardia followed by tachycardia. Bradycardia was abolished by atropine; tachycardia was suppressed by propranolol and previous treatment with reserpine. At zero [Ca
2+
]o, threshold concentrations of Ba
2+
for inducing automaticity were lower than those at normal [Ca
2+
]o. Ba
2+
markedly prolonged the action potential plateau in solutions deprived of Ca
2+
. The size of the overshoot was increased and the rise time was shortened despite a significant reduction in the resting potential. Ba
2+
partly restored atrial contractility abolished at zero [Ca
2+
]o. Each electrical discharge evoked an individual contraction, and a sufficiently fast discharge led to summation of the contractions. Pacemaker activity induced by Ba
2+
was suppressed by adding Ca
2+
and Mg
2+
. The threshold potential was raised by Ca
2+
and Mg
2+
. Threshold concentrations of Ba
2+
for inducing automaticity were not influenced by previous treatment with reserpine.
It is postulated that Ba
2+
antagonizes the movement of K
+
across the membrane, resulting in a decrease in the resting potential and a prolongation of the action potential duration, and that Ba
2+
serves as a current-carrying ion at zero [Ca
2+
]o. It seems unlikely that cardiac norepinephrine participates in pacemaker activity induced by Ba
2+
.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Reference34 articles.
1. Influence of drugs on the irritability and automaticity of heart muscle;GRETNER T. H.;J Pharmacol Exp Ther,1950
2. Effects of Barium Chloride on Resting and Action Potentials of Ventricular Fibers of the Frog
3. Elektrophysiologische Untersuchungen �ber die Barium-induzierte Schrittmacher-Aktivit�t im isolierten S�ugetiermyokard
4. Ca- and K-free solution and pacemaker activity in mammalian myocardium;MULLER P.;Helv Physiol Pharmacol Acta,1965
5. Pacemaker potentials in left auricular tissue of the guinea pig;CARMEUET E. E.;Arch Int Physiol,1965
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