Development of force-velocity relation and rise of isometric tetanic tension measure the time course of different processes.

The time course of the contractile process was investigated in the presence of AR-L 115BS, a twitch potentiator which is thought to increase the rate of the Ca2+ binding by troponin and to improve the Ca2+ mobilization from the sarcoplasmic reticulum. AR-L 115BS increased markedly the rate of development of the force-velocity (T-V) relation and of the isometric tetanic tension. The effect on the rate of development of the T-V relation was however substantially more intense than that on the speed of rise of tetanic tension, thus reducing considerably the isometric tension level at which the T-V relation attained its final characteristics. The velocity of shortening under zero load and the degree of curvature of the T-V relation were not affected by AR-L 115BS. These findings support the view that the development of the T-V relation and the rise of the isometric tetanic tension measure the time course of two different processes.