抄録
It is well known that the muscle produces more force at a longer sarcomere length (SL). By x-ray diffraction study (at BL45XU in SPring 8), the equatorial reflection ratio of I(1,0) and I(1,1) was well related to the peak tension in rat papillary muscle, showing that a larger tension accompanies a smaller ratio. Thus, the tension, SL, and ratio are all related to each other: at a longer SL, the twitch tension is larger and the intensity ratio smaller. It is predictable that the peak tension and the I(1,0)/I(1,1) intensity ratio in systole are also related to each other since both are related to the SL. However, these two parameters are more strongly correlated. In a small range of SL, the peak tension is larger when the intensity ratio is smaller, showing that this relation holds regardless of the SL. When the same data points were classified into three groups by the peak tension, no significant correlation was found between the SL and the I(1,0)/I(1,1) intensity ratio within each group. Similarly, no correlation was found between the twitch tension and the SL when the data were classified into three groups by the I(1,0)/I(1,1) intensity ratio. Thus, the correlation between the intensity ratio and the tension, is not mediated by the SL, but holds even when the tension varies depending on the specimen at the same SL. This is consistent with the interpretation that the intensity ratio in systole is related to the number of cross-bridges formed in contraction. [Jpn J Physiol 54 Suppl:S121 (2004)]
