Two Components of Transient Outward Current in Canine Ventricular Myocytes

• Published in: Circulation research 1989-04, Vol.64 (4), p.633-647
• Main Authors: Tseng, Gea-Ny, Hoffman, Brian F
• Format: Article
• Language: English
• Subjects: 4-Aminopyridine; Action Potentials; Aminopyridines - pharmacology; Animals; Biological and medical sciences; Caffeine - pharmacology; Calcium - metabolism; Calcium - physiology; Cells, Cultured; Dogs; Electrophysiology; Fundamental and applied biological sciences. Psychology; Heart; Heart Conduction System - cytology; Heart Conduction System - drug effects; Heart Conduction System - physiology; Heart Ventricles - cytology; Kinetics; Manganese - pharmacology; Myocardium - cytology; Myocardium - metabolism; Ryanodine - pharmacology; Sarcoplasmic Reticulum - metabolism; Ventricular Function; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.64.4.633

Repolarization during phase 1 of cardiac action potential is important in that it may influence both impulse conduction in partially depolarized tissue and action potential duration. Thus, it is important to know the properties and regulation of the underlying currents. In about 50% of canine ventricular myoeytes, the action potential displays a phase 1 of fast repolarization and a prominent notch between phase 1 and the plateau. A transient outward current is responsible for both. This current is composed of two componentsone (Ito1) blocked by 4-aminopyridine and the other (Ito2) blocked by manganese. In the present study, we characterized each of the components in isolation from the other. Both had an activation threshold between -30 and -20 mV. At the same voltage, Ito1 was larger than Ito2 and had a shorter time to peak. The peak current-voltage relationship for Ito1 was almost linear, but that for Ito2 was bell-shaped. Ito1 decayed during sustained depolarization with a single exponential time courseτ