Measurement of sarcomere behavior at multiple locations along single permeabilized muscle fibers.

The measurement of sarcomere lengths of single muscle fibers has been limited to sampling of a single region of the fiber although repeated samplings were possible. During studies that sample only a single region of the fiber, investigators are unable to correlate the measured length changes of the sarcomeres with overall length changes of the fiber. The lack of data from multiple regions leaves several issues of muscle behavior unexplained and hinders investigations of contraction induced injury. In the present study, instrumentation was designed and tested that permits, during a single event, the measurement of sarcomere lengths in single muscle fibers at multiple regions along a fiber. Multiple regions along the fiber were sampled by translating a laser beam and sequentially recording the diffraction patterns. The laser sweep was considerably faster than the motion of the sarcomeres. Consequently, during a single sweep, a map of regional sarcomere behavior was recorded with little or no motion of the sarcomeres. Following characterization of the apparatus, measurements of the length of sarcomeres at multiple regions along passive single permeabilized fibers were obtained while the fibers were held at a constant length and during constant-velocity stretches. The results from these tests supported two hypotheses. The first, when passive fibers were subjected to repeated stretches of ∼20% strain, and returned to the initial fiber length after each stretch, the sarcomere lengths of different regions along the fiber were reproducible (less than 2% coefficient of variation), The second, when passive fibers were subjected to repeated stretches of ∼20% strain, the changes in sarcomere lengths of the different regions along the fiber during the stretch were reproducible (less than 2% coefficient of variation). Although highly reproducible, the dispersion of sarcomere lengths along the fiber indicated that certain regions of a passive fiber had a predisposition to longer resting lengths and others to shorter resting lengths. The variation in the intrinsic length of different groups of sarcomeres must be dependent upon the non-contractile elements in the fiber. During repeated stretches, reproducible behavior provides a consistent baseline for future experiments where sarcomere behavior is likely to be more variable.PhDApplied SciencesBiomedical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132692/2/9977267.pd