At extremes of shortening under low afterload, some smooth muscles show a marked increase in axial stiffness (Meiss, R. A., J. Muse. Res. Cell Motil. 13. 190-198, 1992) This effect, which depends chiefly on the isotonic muscle length, has been attributed to an internal load arising from compressed tissue strained in a radial direction. Alternatively, increased stiffness at short lengths may reflect internal cellular properties arising from the myofilament array and/or cytoskeleton. Such cellular properties have been implicated in length history effects on the contractility of shortening muscle. Several protocols were used to aid in distinguishing between these effects. 1 : Using oscillatory length perturbations applied to electrically stimulated canine trachealis strips, length-dependent stifrhess during shortening was measured in contractions beginning at a series of starting lengths (< LI Regardless of the starting length, the stiffness curves were superimposable at alllengths, although contractions begun at shorter lengths also reached shorter absolute lengths. 2: During isometric contraction (at L0) muscles were suddenly shortened by 20% of their length (to L,) After a few seconds of isometric contraction, lightly-loaded isotonic contractions were made and were compared with similar isotonic contractions beginning at L2 without any prior length step. The step reduced the isometric force, the total extent of shortening, and the shortening velocity at any given length. However, the length-stiffness curves of the two isotonic contractions were superimposable over the regions of length encountered, indicating that the length-dependent stifrhess was not sensrtrtive to mechanicallyinduced contractility changes.
|Original language||English (US)|
|State||Published - Dec 1 1996|
ASJC Scopus subject areas
- Molecular Biology