Effects of tetrodoxin and verapamil on triggered activities induced by cesium chloride in cat heart in vivo

Cesium chloride (CsCl, 0.5 mmol.kg-1, iv) decreased sinus rate, shortened monophasic action potential duration (MAPD), and induced early after depolarization (EAD) in cat heart in vivo. Tetrodotoxin (TTX, 8 micrograms.kg-1, iv) suppressed the prolonged MAPD. TTX and verapamil (Ver, 0.5 mg.kg-1, iv) decreased the EAD amplitude and suppressed the sustained ventricular tachycardia induced by repeated injection of CsCl. These results suggested that the normal inward sodium "window" current and slow inward current (Isi) carried by calcium or sodium appear to be essential for the occurrence of EAD and triggered arrhythmia if repolarization outward potassium current are blocked.