Light diffraction by striated muscle fibres in the transverse direction.

The intensity of the diffraction line, the transverse intensity, of a single skeletal muscle fibre illuminated at normal incidence with a laser beam decayed monotonically to zero at both ends of the diffraction line. This characteristic decay was observed for most illuminated spots of the fibre. However, for a few spots the transverse intensity showed distinctive oscillations. The intensity distribution of the diffraction line is explained by a diffraction model in which the muscle fibre acts as a bundle of randomly packed myofibrils of different diameters. The equatorial intensity was calculated as a function of myofibrillar diameter dispersion. The comparison between the theoretical curves and measurements yields an estimation for the myofibrillar diameter dispersion. The calculations predict that the transverse intensity would exhibit oscillations when the diameter dispersion is less than 22%. Finally, the diameter dispersions estimated by light diffractometry and electron microscopy are compared.