[Study of the mechanics and small-angle equatorial x-ray pattern of the frog skeletal muscle during transition and rigor at different temperatures].

Mechanical characteristics and low-angle equatorial X-ray patterns from frog sartorius muscle passing into iodoacetate rigor under isometric conditions at temperatures 2 degrees-25 degrees C were studied. It is ascertained that during the rigor tension development at all the temperatures Z-reflection intensity increases and those of the (10), (11), (20), (21) and (30) reflections decrease. The last three reflections disappear then still in the phase of the rigor tension development. It is found that the sarcomere lengths remain not always invariable, especially at high temperatures, when the muscle passes into rigor, and can both decrease and increase in the sample place which is investigated by means of X-ray diffraction method. It is shown that the decrease of the I10/I11 relation in some experiments at high temperatures is only due to the sarcomere length decrease. The merging time of the Z and (11) reflections depends both on the temperature and on the sarcomere length change. Thus essential changes correlated with the rigor tension development, and resulted in the Z-reflection intensity increase take place in tetragonal lattice of Z-band and in the I-band region located near Z-band. In A-band the hexagonal lattice order change for the worse is marked only. It is proposed that the mechanism of the rigor tension development differs from that of tension development in ordinary contraction of the skeletal muscle.