Abstract
We developed the electromagnetic apparatus to perform quick change in load in the motility system using the magnetizable beads on which myosin thick filaments from molluscan smooth muscle or green algae, Chara, myosin were attached. The quick change in load to the beads (diameter 4.5 µm) was applied in the range of 0–85 pN. The movement of beads was recorded by video-system and analyzed with special software. 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. The change in the load-sustaining ability was measured by double load step. The backward velocity at the second constant test load was smaller when the first preceding step was increased, suggesting that the ability to sustain load was higher with higher preceding step. The above-mentioned phenomena were observed both in molluscan thick filaments and in Chara myosin and the time course of the movement of a bead is quite similar to those observed previously in frog single muscle fibers, suggesting that the velocity transients are the intrinsic properties induced by the interaction between actin and myosin, irrespective of the hexagonal lattice structure of filaments, the regular sarcomere structure and myosin type, namely that the molecule of myosin itself has the ability to adjust to mechanical circumstances.
