Approaches to physical fitness and sports medicine through X-ray diffraction analysis of striated muscle

Abstract

X-ray diffraction analysis is a method to obtain information about periodically repeated structures. When striated muscle is irradiated with X-ray, many of the reflections and the layer lines, which convey information about molecular structures within the muscle fiber, are obtained without chemical modification. Two of the strong equatorial reflections, 1,0 reflection arising from a thick filament array and 1,1 reflection arising from a thick and thin filament array appear on the equator giving information about distance and mass distribution on a radial plane. Thus a 1,1/1,0 intensity ratio is a good index of radial distribution of myosin heads. Meridional reflections and layer lines, such as a myosin reflection of the 14.3 nm repeat and myosin or actin layer lines, give information about longitudinal arrangement of the molecules. Since they are affected by the movement of the myosin heads and the shifting motion of troponin-tropomyosin on the actin filament, they can be used to detect conformational changes of contractile and regulatory systems upon muscle activation. The X-ray diffraction method has been applied to yield fruitful results for many problems such as muscle atrophy by disuse, functional modulation by myosin regulatory light chain phosphorylation, differential characteristics of slow and fast skeletal muscle structure, and pathogenesis of some types of the familial myopathy. The approach using X-ray diffraction analysis will continuously serve as a potent tool for resolving problems in the field of physical fitness and sports medicine.

Lattice arrangement of myosin filaments correlates with fiber type in rat skeletal muscle

“…To our knowledge, only three "pure" tetrapod slow muscles have previously been examined by X-ray diffraction (most muscles are not pure, but have a mixture of fast and slow fibers [29]). A study of rat SOL and EDL, under conditions designed to phosphorylate or dephosphorylate the regulatory light chains, showed little to no lattice sampling on ML1 of SOL, and made no conclusion about the type of myosin filament lattice present [30]; the conditions used for these experiments may have caused significant disordering of the myosin heads, thus weakening the myosin layer lines and their sampling. A comparison of rat SOL and psoas muscles focused on crossbridge behavior and made no mention of lattice structure [31].…”

Lattice arrangement of myosin filaments correlates with fiber type in rat skeletal muscle

“…To our knowledge, only three "pure" tetrapod slow muscles have previously been examined by x-ray diffraction (most muscles are not pure, but have a mixture of fast and slow fibers; Schiaffino and Reggiani, 2011). A study of rat SOL and EDL, under conditions designed to phosphorylate or dephosphorylate the regulatory light chains, showed little to no lattice sampling on ML1 of SOL, and made no conclusion about the type of myosin filament lattice present (Yamaguchi et al, 2016); the conditions used for these experiments may have caused significant disordering of the myosin heads, thus weakening the myosin layer lines and their sampling. A comparison of rat SOL and psoas muscles focused on cross-bridge behavior and made no mention of lattice structure (Horiuti et al, 1997).…”