AJP - Cell Physiology, Vol 259, Issue 2 C266-C278, Copyright © 1990 by American Physiological Society
Sarcomere dynamics during isotonic velocity transients in single frog muscle fibers
H. L. Granzier, A. Mattiazzi and G. H. Pollack
Center for Bioengineering, University of Washington, Seattle 98195.
If the load on a tetanized fiber is abruptly changed to a new steady value,
the ensuing fiber length change shows the well-known "isotonic velocity
transient," in which the velocity oscillates before settling at some steady
value. We studied sarcomere dynamics during these transients using two
methods: optical diffraction and a segment-length method. Our principal aim
was to determine whether these transients might be a reflection of the fact
that sarcomere shortening is often found to be stepwise. We found that
pauses in sarcomere shortening occurred during the low-velocity phases of
the transient and that steps of sarcomere shortening occurred during the
high-velocity phases. Thus the isotonic transient appears to arise from the
steps. In addition to the isotonic transient, we studied the well-known
isometric transient, in which fiber length is abruptly changed, and ensuing
tension response is measured. Again, we found that the transient may be a
reflection of the stepwise shortening pattern.
