CONTRACTILITY OF ACTOMYOSIN BANDS PREPARED FROM NORMAL AND FAILING HUMAN HEARTS1

Abstract

Actomyosin bands were prepared from normal and failing human hearts obtained at necropsy. ATP-induced afterloaded contractions were recorded without friction by means of a new null seeking device. The time interval (2-6 hours) between death of the patient and the preparation of actomyosin did not affect the shortening of the actomyosin bands. Actomyosin bands prepared from normal hearts demonstrated a reverse relationship between load and percentage shortening. Nicotine caused a slight diminution in the contractility of the bands, while CaCl2 and digoxin, when added separately, had no effect. When combined, CaCl2 and digoxin increased the shortening of the bands. The contractility of actomyosin bands prepared from failing human hearts was significantly diminished. Digoxin failed to correct this defect, but the combination of digoxin and CaCl2 restored shortening of the bands to normal.