Abstract
The sartorius muscles from a bullfrog were used. The X-ray patterns were recorded by an X-ray CCD detector with a time resolution of 15 msec. When the skeletal muscle is stretched slowly at the plateau of the isometric tetanus, the tension increases during the stretch. When the length change terminates, the tension starts to return to a new tension level, which is higher than the initial isometric level. In a release, the tension behaves in a similar but opposite way. The effect of these muscle length changes on the intensity of the 3rd meridional reflection (M3), which arises from the 14.3 nm repeat of the myosin heads was examined. It was found that M3 increases during stretch and decreases during release if the applied length change is smaller than 1% of the muscle length(Lo). When the applied length change is larger than 1%, both stretch and release induce the decrease in M3. When a sinusoidal length change (amplitude = 1%Lo) is applied to the tetanized muscle, M3 increases and decreases in parallel with the applied length change. On the other hand, when the length change is larger than 1%Lo (for example, 3%Lo), M3 decreases both in stretching and releasing phases. [Jpn J Physiol 55 Suppl:S118 (2005)]
