Sarcomere dynamics during isotonic velocity transients in single frog muscle fibers.
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.
Granzier
H L
HL
Center for Bioengineering, University of Washington, Seattle 98195.
Mattiazzi
A
A
Pollack
G H
GH
D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods; D066298:In Vitro Techniques; D007700:Kinetics; D008954:Models, Biological; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology*; D011896:Rana temporaria; D012518:Sarcomeres / Q000502:physiology*; D013997:Time Factors