纳米医学与纳米技术杂志

抽象的

Visualization and Recording of Structural Changes in Hydrated, Living Muscle Myofilaments using the Gas Environmental Chamber

Haruo Sugi, Takuya Miyakawa, Masaru Tanokura, Shigeru Chaen, Hiroki Minoda and Tsuyoshi Akimoto

Although more than 50 years have passed since the monumental discovery of ATP-dependent sliding filament mechanism in muscle contraction, the mechanism of cyclic attachment-detachment cycle between myosin heads extending from myosin filaments and corresponding sites on actin filaments still remains to be a matter for debate and speculation. Using the gas environmental chamber (EC) attached to an electron microscope, we have succeeded in recording images of hydrated myosin filaments, with gold particle position markers attached to individual myosin heads. In the absence of ATP, the position of individual myosin heads does not change appreciably with time, indicating stability of time-averaged myosin head mean position. On ATP application, individual myosin heads move parallel to the filament axis by ~6 nm. At both sides of the filament bare region, across which myosin head polarity is reversed, individual myosin heads move away from, but not towards, the bare region, indicating that the observed myosin head movement
corresponds to the recovery stroke, associated with reaction, M + ATP → M·ADP·Pi. After exhaustion of applied ATP, individual myosin heads return towards their initial position. Recently, we have further succeeded in recording ATPinduced myosin head power stroke in the presence of actin filaments, and have found that the amplitude of power stroke in the isometric condition is ~3 nm, and increases to ~5 nm at low ionic strength, in accordance with the physiological experiments that Ca2+-activated force increases ~two fold at low ionic strength. These findings about the novel features of ATP-induced myosin head movement indicate that the EC is an extremely powerful tool, which enables us to visualize and investigate behavior of individual myosin heads in living, hydrated myosin filaments, retaining their physiological function. Finally, we emphasize that our EC work still remains to be the only attempt to investigate function of hydrated
macromolecules.