|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1993 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1992 : ¥1,600,000 (Direct Cost : ¥1,600,000)
To obtain information about the kinetics of force-generating processes in the actomyosin crossbridges which retain naturally ordered arrangement, we studied the force-velocity relations in sliding movements of native thick filaments along F-actin cables.
Native thick filaments (length, up to 30 mum) were isolated from the anterior byssus retractor muscle (ABRM) of Mytilus edulis and attached to polystirene microbeads (diameter, 4mum) coated previously with poly-L-lysine. The beads were placed on F-actin cables of perfused Chara internodal cells, which was then mounted on a rotating stage of a centrifuge microscope, and the velocities of steady state, sliding movements of the beads in the presence of ATP(3mM) were measured under both positive(opposite to the direction of sliding)and negative(same as that of sliding)centrifugal loads(up to 30 pN). Under the positive load, the force-velocity relation was well described, in its most part (with the exception of a small "hump" above 0.8P0), by Hill equation and appeared markedly similar to that for frog single muscle fibers. Under the negative load, the sliding velocity initially increased with force beyond the maximal unloaded velocity (V0), then appeared to reach a steady level at 2-3V0 until the beads were eventually detached from actin cables. The results suggest that the minimal unit responsible for the classical force-velocity relations is several tens or hundreds of crossbridges, and their ordered arrangement along thick filaments plays an important role in determining the mechanical properties of muscle contraction.