This study was undertaken to determine whether glycerol-extracted rabbit psoas muscle fibers can develop tension and shorten after being stretched to such a length that the primary and secondary filaments no longer overlap. A method was devised to measure the initial sarcomere length and the ATP-induced isotonic shortening in prestretched isolated fibers subjected to a small preload (0.02 to 0.15 P0). At all degrees of stretch, the fiber was able to shorten (60 to 75 per cent): to a sarcomere length of 0.7 µ when the initial length was 3.7 µ or less, and to an increasing length of 0.9 to 1.8 µ with increasing initial sarcomere length (3.8 to 4.4 µ). At sarcomere lengths of 3.8 to 4.5 µ, overlap of filaments was lost, as verified by electron microscopy. The variation in sarcomere length within individual fibers has been assessed by both light and electron microscopic measurements. In fibers up to 10 mm in length the stretch was evenly distributed along the fiber, and with sarcomere spacings greater than 4 µ there was only a slight chance of finding sarcomeres with filament overlap. These observations are in apparent contradiction to the assumption that an overlap of A and I filaments is necessary for tension generation and shortening.
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1 October 1965
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October 01 1965
CONTRACTILITY AND ULTRASTRUCTURE IN GLYCEROL-EXTRACTED MUSCLE FIBERS : I. The Relationship of Contractility to Sarcomere Length
Frits Carlsen,
Frits Carlsen
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
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Franklin Fuchs,
Franklin Fuchs
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
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Gustav G. Knappeis
Gustav G. Knappeis
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
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Frits Carlsen
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
Franklin Fuchs
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
Gustav G. Knappeis
From the Institute of Neurophysiology and the Physical Laboratory II. H. C. Ørsted Institute, University of Copenhagen, Copenhagen, Denmark.
Dr. Fuchs' present address is the Department of Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
Received:
August 25 1964
Online ISSN: 1540-8140
Print ISSN: 0021-9525
1965
J Cell Biol (1965) 27 (1): 25–34.
Article history
Received:
August 25 1964
Citation
Frits Carlsen, Franklin Fuchs, Gustav G. Knappeis; CONTRACTILITY AND ULTRASTRUCTURE IN GLYCEROL-EXTRACTED MUSCLE FIBERS : I. The Relationship of Contractility to Sarcomere Length . J Cell Biol 1 October 1965; 27 (1): 25–34. doi: https://doi.org/10.1083/jcb.27.1.25
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