QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online July 2, 2004
Journal of Experimental Biology 207, 2787-2791 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01095

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Peterson, D. R. Articles by Herzog, W. Search for Related Content PubMed PubMed Citation Articles by Peterson, D. R. Articles by Herzog, W.

Force enhancement in single skeletal muscle fibres on the ascending limb of the force–length relationship

Daniel R. Peterson, Dilson E. Rassier and Walter Herzog^*

University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4

View larger version (7K): [in a new window]   Fig. 1. Representation of the time course of stimulation for the experimental stretches. Here, 0% length refers to the length at which active maximal isometric force was obtained (average sarcomere length about 2.1 µm; Lutz and Rome, 1994). The fibres were activated at an initial length for 1 s (sufficient for the force to reach the maximal isometric force at that length), then stretched 10% of fibre length to the final length in 0.25 s (40% s–1). The fibre was then held at this final length for another 4.75 s (sufficient time for steady-state isometric force to be established; Edman et al., 1982).

View larger version (14K): [in a new window]   Fig. 2. Typical experiment, conducted with one fibre. (A–C) Two isometric force traces with the fibre at the initial length (i, bottom trace), and the final length (f, middle trace), as well as the stretch contraction from the initial to the final fibre length (s, top trace). In A, the final length corresponds to the optimal length for force development; i.e. at this length, the purely isometric force was maximal. Note that the steady-state force enhancement is greater than any of the isometric forces, although only by a small amount in C. Initial lengths: –10%, –15% and –20% for A, B and C, respectively. Stretch speed was 40% of fibre length s–1, and stretch amplitude was 10% of fibre length in all cases.

View larger version (14K): [in a new window]   Fig. 3. Mean ascending limb portion of the force–length relationship (gray circles, solid line) and steady-state forces (mean ±1 S.D.) following stretch tests (black squares, connected to initial lengths by broken lines) in lumbrical fibres. Forces were normalized with respect to the maximal isometric force (dotted line) for comparison across fibres. Fibre lengths were normalized relative to the optimal fibre length (0%), i.e. the length at which the isometric force was greatest. Note that steady-state force enhancement for stretches beginning at lengths –10 and –15% produced average forces greater than the isometric force at optimal length (0%). Optimal average sarcomere length was based on Lutz and Rome (1994), who demonstrated that maximal force in single frog fibres for fixed-end contractions (as produced here) correspond to an average sarcomere length of 2.1 µm. The remaining average sarcomere lengths were calculated proportionally to the fibre length change.