Quasi-Elastic Light-Scattering Studies of Single Skeletal Muscle Fibers
Measurements were made of the intensity autocorrelation function, g(2)[τ], of light scattered from intact frog muscle fibers. During the tension plateau of an isometric tenanus, scattered field statistics were approximately Gaussian and intensity fluctuations were quasi-stationary. The half time, τ1/2, for the decay of g(2)[τ] was typically 70 ms at a scattering angle of 30 degrees. The decay rate, 1/τ1/2, of g(2)[τ] varied roughly linearly with the projection of the scattering vector on the fiber axis. 1/τ1/2 was greater during the tension creep phase of tetani of highly stretched fibers, but was roughly independent of sarcomere length during the tension plateau. g(2)[τ] measured during rest or on diffraction pattern maxima during isometric contraction were flat with low amplitudes. These results are consistent with a model of a 200-μm segment of an isometrically contracting fiber in which scattering material possesses relative axial velocities of 1-2 μm/s accompanied by relative axial displacements greater than 0.1 μm. The slow (1-2 μm/s) motion of one portion of the fiber relative to another observed under the microscope (500x) during isometric contraction is consistent with the light-scattering results. Structural fluctuations on the scale of the myofibrillar sarcomere which may arise from asynchronous cycling of cross-bridges must involve relative axial velocities less than 3 μm/s or relative axial displacements less than 0.05 μm.
Haskell, RC, Carlson, FD. Quasi-elastic light-scattering studies of single skeletal muscle fibers. Biophys J. 1981;33(1): 39-62.