抄録
Using the gas environmental chamber,with which electron microscopic images of living muscle thick filaments can be recorded on the imaging plate, we have attempted to record ATP-induced cross-bridge movement at both sides of the thick filament bare region, across which the cross-bridge polarity is reversed. Large bipolar thick filaments were prepared by slowly polymerizing rabbit skeletal muscle myosin. Without ATP application, the position of gold particles, attached to the junctional peptide between 50 and 23kDa fragments of myosin heavy chain with a site-directed antibody, did not change appreciably with time, indicating that the time-averaged cross-bridge position remained almost unchanged despite thermal motion. On application of ATP to myosin filaments, the cross-bridges were found to move by 5-8nm in the direction away from, but not towards, the filament bare region. Since thin filaments are absent in the experimental system, the ATP-induced cross-bridge movement is associated with the formation of intermediate, M-ADP-Pi, and is therefore regarded as the cross-bridge preparatory stroke, having the amplitude identical with, and the direction opposite to, the cross-bridge power stroke. We thank Japan Electron Optics Laboratory for providing facilities to carry out our work. [J Physiol Sci. 2008;58 Suppl:S64]
