Light diffraction intensity from muscle fibres in different osmotic solutions: measurement of equilibration time.

A new method for evaluating the osmotic equilibration time of striated muscle fibres is described. Single fibres from the semitendinosus muscles of frog were illuminated normally with a He-Ne laser. The first-order diffraction intensity was measured continuously after the tonicity of the fibre's bathing solution was changed abruptly. Hypertonicity decreased while hypotonicity increased the intensity. The time course of the intensity decrease or increase followed closely a simple exponential with a single time constant. It is proposed that the time constant associated with the diffraction intensity transient is a true representation of the equilibration process. A simple diffraction model provides a relationship between diffraction intensity and the diameter of the muscle fibre. This relationship is used to explain the diffraction intensity of fibres in different osmotic solutions.