Optical diffraction study of muscle fibers. II. Electro-optical properties of muscle fibers.

When an electric field is applied along the fiber axis, the intensities of all observable optical diffraction lines of skeletal muscle fibers increase. This electro-optical effect was extensively studied and it was confirmed that the effect is due to the interaction between electric dipole moments of thin filaments and the applied field. From the present study on the intensity modulation due to applied field in sinusoidal and square forms, we confirmed that (1) the thin filament is a semiflexible rod, (2) the second order mode of the bending motion of thin filaments contributes to the electro-optical effect of muscle fibers at higher frequencies of a sinusodidal field or shorter durations of a square field, (3) the induced moment has no appreciable effect, and (4) the estimated value of the flexural rigidity of thin filaments strongly depends on the concentrations of free calcium ions in the myofibrillar space.