Sarcomere lengths of thick skeletal muscle specimens measured under an epi-illumination-type polarization microscope.

The purpose of this study was to measure sarcomere lengths of thick muscle fiber bundles at resting and at isometric tetanic contractions. We developed a novel measurement system using an epi-illumination-type polarization microscope and an image processing algorithm using an ellipse-type Gabor filter. Images with striation patterns of frog skeletal muscle were obtained by the microscope and the image processing algorithm. Individual lengths of 10 consecutive sarcomeres of a single muscle fiber were measured by gauging each width of the striation pattern, which was proved to be derived from striation structures of the single fiber by performing experiments using different polarization lights and different focus depths. At the resting state, each sarcomere length was identical at the fixed muscle length and in proportion to the length ranging over 91-123% of the natural length. Each sarcomere length was unchanged at the steady state during isometric tetanic contractions. Individual sarcomere lengths in the central part of the skeletal muscle were identical at resting and at isometric tetanic contractions even in the thick muscle fiber specimen.