Abstract
The transient mechanical responses after quick change in load or in length were observed in the living single muscle fibers and these experiments contributed greatly to proposing the hypothesis of cross-bridge rotation in muscle contraction. Sugi and Tsuchiya (1981) also studied the transient length changes in living single fibers when the quick increase in load was applied during shortening. We developed the electromagnetic apparatus to perform quick change in load in the motility system consisted of the magnetizable beads with myosin thick filaments from molluscan smooth muscle or myosin of Chara and actin cables in the Chara internodal cells. In the present experiment, the quick change in load (about 10 ms) to the beads (diameter 4.5μm) was applied in the range of 0-85 pN. The movement of beads was recorded by video-system and analyzed with special software (Swallow series, Digimo). When the quick increase in load was applied during the movement of beads under no load, the beads showed the transient movement to the reverse direction before the steady slower movement to normal direction. When the application of load was stopped, the beads showed transient fast phase of movement. These velocity transients are quite similar to those observed previously in single fibers and suggesting that the velocity transients are the intrinsic properties induced by the interaction between actin and myosin without hexagonal lattice structure of filaments or regular sarcomere structure irrespective of myosin types. [Jpn J Physiol 54 Suppl:S117 (2004)]
