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This Article Full Text Full Text (PDF) All Versions of this Article: 297/5/C1211    most recent 00233.2009v1 Alert me when this article is cited Alert me if a correction is posted Citation Map 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 Google Scholar Articles by Pavlov, I. Articles by Rassier, D. E. PubMed PubMed Citation Articles by Pavlov, I. Articles by Rassier, D. E.

Methods in Cell Physiology

The mechanical behavior of individual sarcomeres of myofibrils isolated from rabbit psoas muscle

Department of Kinesiology and Physical Education, McGill University, Montreal, Quebec, Canada

Submitted 26 May 2009 ; accepted in final form 25 August 2009

The goal of this study was to develop a system to experiment with sarcomeres mechanically isolated from skeletal muscles. Single myofibrils from rabbit psoas were transferred into a temperature-controlled (22°C or 15°C) experimental chamber, and sarcomeres were isolated using precalibrated glass microneedles that were pierced externally, adjacent to the Z-lines. The force produced during activation was measured by tracking the displacement of the microneedles, and the sarcomere and half-sarcomere changes were measured by continuously tracking the Z-lines and A-bands position during the experiments. Sarcomeres produced a stress (force/cross-sectional area) of 112.75 ± 4.96 nN/µm² (15°C) and 128.47 ± 5.58 nN/µm² (22°C) at lengths between 2.0 µm and 2.4 µm. The descending limb was fitted with linear regression for length between 2.4 µm and 3.5 µm, which provided an abscissa extrapolating to 3.87 µm. The force-length relation was remarkably similar to a theoretical curve based on the degree of filament overlap. During sarcomere activation, we tracked the distance between the center of the A-band and the Z-lines. At lengths below 1.6 µm, movements of A-band were not detected. A-band movements increased with length to achieve a maximum displacement of 59.40 ± 10.1 nm from the center at 2.0 µm–2.4 µm. A-band displacement decreased linearly in sarcomere lengths between 2.6 µm and 3.6 µm. A technique for monitoring force and length in single sarcomeres isolated from myofibrils represents a reliable technique to evaluate contractile mechanisms at the most basic, intact level of muscle organization, opening the possibility to clarify long-standing issues in the field of muscle contraction.

cross-bridges; force-length relation; myosin-actin interaction