We analyzed the microstructure in the first-order laser diffraction line from both resting and tetanically contracting single twitch fibers from frog anterior tibial muscle to see if the distribution of sarcomere lengths is continuous or discrete. Measuring the distance between adjacent microstructural elements lying parallel, we plotted a histogram of the corresponding differences of sarcomere length. The histograms obtained both from resting and contracting fibers had a prominent peak at approximately 12-14 nm. The result suggests that the sarcomere length distribution may be discrete with unit separation of approximately 12-14-nm sarcomere length.
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