AJP - Heart and Circulatory Physiology, Vol 243, Issue 5 767-H778, Copyright © 1982 by American Physiological Society

ARTICLES

Different forms of spontaneous discharge induced by strophanthidin in cardiac Purkinje fibers

S. Ishikawa and M. Vassalle

The effect of strophanthidin on spontaneous discharge in canine cardiac Purkinje fibers perfused in vitro was studied during periodic interruptions (pauses) of the electrical drive. The results show that 1) strophanthidin initially increases the slope of diastolic depolarization and thereby induces a slow rhythm that accelerates progressively during the pause and becomes faster during the increasing strophanthidin inotropy; 2) oscillatory potentials appear only when strophanthidin inotropy reaches its peak (or actually declines) and may cause either a few fast action potentials during the pause or a fast rhythm that eventually overcomes the driven beats; 3) the slow rhythm is eliminated by cesium; 4) the fast rhythm is eliminated by tetrodotoxin; and 5) oscillatory potentials caused by high calcium, norepinephrine, or low potassium are similarly affected by cesium or tetrodotoxin. It is concluded that strophanthidin enhances diastolic depolarization, thereby causing the slow rhythm, and induces oscillatory potentials, thereby causing the fast rhythm. Only the oscillatory potentials are related to calcium overload as determined by several different procedures.