Instantaneous force-velocity-length relationship in diaphragmatic sarcomere

Abstract

Coirault, Catherine, Denis Chemla, Jean-Claude Pourny, Francine Lambert, and Yves Lecarpentier. Instantaneous force-velocity-length relationship in diaphragmatic sarcomere. J. Appl. Physiol. 82(2): 404–412, 1997.—The simultaneous analysis of muscle force, length, velocity, and time has been shown to precisely characterize the mechanical performance of isolated striated muscle. We tested the hypothesis that the three-dimensional force-velocity-length relationship reflects mechanical properties of sarcomeres. In hamster diaphragm strips, instantaneous sarcomere length (S L) and muscle length were simultaneously measured during afterloaded twitches. S L was measured by means of laser diffraction. We also studied the influence of initial S L, abrupt changes in total load, and 2 × 10−7 M dantrolene. Baseline resting S L at the apex of the length-active tension curve was 2.2 ± 0.1 μm, whereas S L at peak shortening was 1.6 ± 0.1 μm in the preloaded twitch and 2.1 ± 0.1 μm in the “isometric” twitch. Over the whole load continuum and at any given level of isotonic load, there was a unique relationship between instantaneous sarcomere velocity and instantaneous S L. Part of this relationship was time independent and initial S L independent and was markedly downshifted after dantrolene. When five different muscle regions were considered, there were no significant variations of S L and sarcomere kinetics along the muscle. These results indicate that the time- and initial length-independent part of the instantaneous force-velocity-length relationship previously described in muscle strips reflects intrinsic sarcomere mechanical properties.