Key result
The laser diffraction method was comparable to light microscopy for measuring sarcomere lengths >1.6 microns, but did not accurately assess contraction for lengths <1.6 microns.
Laser diffraction is inaccurate for measuring highly contracted sarcomeres (<1.6 microns) in chicken pectoralis major muscle compared to light microscopy.
Caution warranted for laser diffraction in contracted muscle models; leaves open validation for cardiac sarcomere research.
The objective of the present study was to compare the effectiveness of a microscopy method with a laser diffraction method for measuring sarcomere lengths of chicken pectoralis major (p. major) muscle fibers exhibiting various contraction states. Chicken p. major muscles were excised from the animals at death. Samples of each muscle were treated with pH-buffered (5.0 and 7.5) isoionic CaCl2, KCl, or ethylene glycol bis-(b-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) solutions in order to produce variability in the degree of fiber contraction. Sarcomere lengths (SL) of the fibers were observed using light microscopy and a laser diffraction method. The methods gave comparable results for sarcomere lengths greater than 1.6 microns. However, for SL less than 1.6 microns, sarcomere contraction was not accurately assessed by the laser diffraction method.
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YOUNG et al. (1990) studied Chicken pectoralis major muscle fibers. Laser diffraction method vs. Microscopy method was evaluated on Sarcomere lengths (SL) of the fibers. The laser diffraction method was comparable to light microscopy for measuring sarcomere lengths >1.6 microns, but did not accurately assess contraction for lengths <1.6 microns.
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