The length–tension curve in muscle depends on lattice spacing

Classic interpretations of the striated muscle length–tension curve focus on how force varies with overlap of thin (actin) and thick (myosin) filaments. New models of sarcomere geometry and experiments with skinned synchronous insect flight muscle suggest that changes in the radial distance between the actin and myosin filaments, the filament lattice spacing, are responsible for between 20% and 50% of the change in force seen between sarcomere lengths of 1.4 and 3.4 µm. Thus, lattice spacing is a significant force regulator, increasing the slope of muscle's force–length dependence.

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The site of paramyosin in insect flight muscle and the presence of an unidentified protein between myosin filaments and Z-line

Journal of Molecular Biology ◽

10.1016/0022-2836(77)90163-2 ◽

1977 ◽

Vol 115 (3) ◽

pp. 417-440 ◽

Cited By ~ 37

Author(s):

Belinda Bullard ◽

Kathleen S. Hammond ◽

Barbara M. Luke

Keyword(s):

Flight Muscle ◽

Insect Flight ◽

Insect Flight Muscle ◽

Myosin Filaments

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A method for determining the periodicity of a troponin component in isolated insect flight muscle thin filaments by gold/Fab labelling

Journal of Cell Science ◽

10.1242/jcs.101.3.503 ◽

1992 ◽

Vol 101 (3) ◽

pp. 503-508

Author(s):

R. Newman ◽

G.W. Butcher ◽

B. Bullard ◽

K.R. Leonard

Keyword(s):

Gold Particle ◽

Colloidal Gold ◽

Striated Muscle ◽

Flight Muscle ◽

Insect Flight ◽

Insect Flight Muscle ◽

Fab Fragment ◽

Thin Filaments ◽

Gold Particles ◽

Almost All

Insect flight muscle has a large component (Tn-H) in the tropomyosin-troponin complex that is not present in vertebrate striated muscle thin filaments. Tn-H is shown by gold/Fab labelling to be present at regular intervals in insect flight muscle thin filaments. The Fab fragment of a monoclonal antibody to Tn-H was conjugated directly with colloidal gold and this probe used to label isolated thin filaments from the flight muscle of Lethocerus indicus (water bug). The distribution of gold particles seen in electron microscope images of negatively stained thin filaments was analysed to show that the probe bound to sites having a periodicity of approximately 40 nm, which is the expected value for the tropomyosin-troponin repeat. Conjugates of Fab with colloidal gold particles of 3 nm diameter labelled almost all sites. Conjugates with gold particles of 5 nm and 10 nm diameter labelled less efficiently (70% and 30%, respectively) but analysis of the distribution of inter-particle intervals among a number of filaments again gave the same fundamental spacing of 40 nm. The error in the measurements (standard deviation approximately +/− 4.2 for 5 nm gold/Fab) is less than earlier estimates for the size of the gold/Fab complex. Measurements on gold/Fab in negative stain suggest that the bound Fab contributes a shell about 2 nm in thickness around the gold particle. The radius of the probe (about 4.5 nm for 5 nm gold/Fab) would then be consistent with the value of error found. The size of the probe suggests that the gold particle binds to the side of the Fab molecule, rather close to the antibody combining site. The potential resolution of the technique may thus be better than originally expected.

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