Osmotic pressure variations used to elicit oscillations and changes in stiffness of muscle fibers.

By observing diffraction spectra produced by passing a laser beam through stimulated muscle fibers, the magnitude of sarcomere length change and the relative rate of filament sliding were found to decrease in hypertonic solutions. The first order diffraction for both resting and stimulated muscle fibers faded and then returned to its original intensity as the bathing solution was changed from isotonic to hypertonic and then back to isotonic. This is explained as being due to a change in optical contrast between the A and I bands. 7 Hz oscillations were detected at 4 degrees C during stimulation as the fibers equilibrated in hypertonic solutions. The stiffness of resting muscle in the hypertonic solutions increased while the stiffness of stimulated muscle decreased until at a concentration of 3.10 R they were equal. All processes were reversible.