The effect of verapamil on potentiated rest contractions in the rat ventricular myocardium.

The effects of verapamil (0.3 to 30 microM) on potentiated rest contractions (PRC) were studied in isometric contractions of left ventricular papillary muscles of the rat. The post-rest potentiation was studied after rest periods of 5, 10, 15, 30, 60 and 120 s. Verapamil reduced the steady-state force and PRC in a dose-dependent manner. However, PRC were less depressed and the magnitude of this depression decreased as the rest period increased. The time constant of the recovery of steady state force after rest potentiation was shortened. These results indicate that the first PRC are less dependent on calcium entering the cell through the slow channels and apparently more dependent on an intracellular calcium store.