Length-dependent optical diffraction pattern changes in frog sartorius muscle

The length dependence of the laser light diffraction pattern produced by R. pipiens whole sartorius muscle has been examined at rest and during tetanic contraction. The muscle diffraction pattern was scanned by a vidicon camera; camera output was digitized and processed by an on-line digital computer to allow a real line display of a section through the diffraction pattern. Analysis of the first order diffraction line profiles yielded values for line amplitude, intensity, center of gravity, line width and percent dispersion. The calculated dispersion provided a measure of the muscle's sarcomere length distribution. First order line amplitudes and intensities were observed to increase, then decrease, with progressive stretch from 1.0 to 1.3 reference length. The percent dispersion among sarcomeres in resting muscle averaged 11% and was approximately proportional (coefficient = .0341) to length. The amplitude and intensity of zero and first order diffraction lines decreased during tetanus, while the line widths and dispersions increased. First order line intesity during tetanus was maximum at about the same length as during rest, i.e., at approximately 2.5 mu sarcomere length. Sarcomere dispersion increased by about 6% during tetanus.