抄録
X-ray diffraction is a unique method which enables us to measure structural changes of contractile and regulatory proteins in live muscles. When a skeletal muscle is electrically stimulated, calcium is released from sarcoplasmic reticulum and binds to troponin in the thin filament. The calcium binding can be monitored by measuring the intensity of the troponin meridional reflection in the x-ray diffraction pattern. Using high flux x-rays from SPring-8, we measured the time course of this intensity change at the time resolution of up to 0.5 ms in a frog skeletal muscle. At 8°C, the onset of the intensity change was about 4 ms after the stimulus, much earlier than intensity changes of myosin-related reflections and the tension development. It also proceeded the latency relaxation in tension. The intensity change of the troponin reflection showed a marked delay to the rise in the intracellular calcium concentration, suggesting a cooperative nature of the structural change in the thin filament. Results on overstretched muscle and double-pulse stimulation will be also presented and discussed. [J Physiol Sci. 2008;58 Suppl:S64]
