Binding of Myosin Cross-Bridges to Thin Filaments of Rabbit Skeletal Muscle

We investigated the molecular mechanism by which troponin (Tn) regulates the Frank-Starling mechanism of the heart. Quasi-complete reconstitution of thin filaments with rabbit fast skeletal Tn (sTn) attenuated length-dependent activation in skinned porcine left ventricular muscle, to a magnitude similar to that observed in rabbit fast skeletal muscle. The rate of force redevelopment increased upon sTn reconstitution at submaximal levels, coupled with an increase in Ca2+ sensitivity of force, suggesting the acceleration of cross-bridge formation and, accordingly, a reduction in the fraction of resting cross-bridges that can potentially produce additional active force. An increase in titin-based passive force, induced by manipulating the prehistory of stretch, enhanced length-dependent activation, in both control and sTn-reconstituted muscles. Furthermore, reconstitution of rabbit fast skeletal muscle with porcine left ventricular Tn enhanced length-dependent activation, accompanied by a decrease in Ca2+ sensitivity of force. These findings demonstrate that Tn plays an important role in the Frank-Starling mechanism of the heart via on–off switching of the thin filament state, in concert with titin-based regulation.

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The dynamics of the interaction between myosin subfragment 1 and pyrene-labelled thin filaments, from rabbit skeletal muscle

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1986.0076 ◽

1986 ◽

Vol 229 (1254) ◽

pp. 85-95 ◽

Cited By ~ 17

Keyword(s):

Skeletal Muscle ◽

Binding Affinity ◽

Kinetic Studies ◽

Rabbit Skeletal Muscle ◽

Fluorescent Label ◽

Weakly Bound ◽

Thin Filaments ◽

Fluorescence Titration ◽

Myosin Subfragment ◽

Myosin Subfragment 1

We have used actin labelled in Cys–374 with N -(1-pyrenyl)iodoacetamide to monitor the dynamics and equilibria of the interaction between myosin subfragment 1 and the actin–troponin–tropomyosin complex in the presence of calcium. These results are compared with those obtained for pure actin and myosin subfragment 1. The sensitivity of this fluorescent label allowed us to measure the binding affinity of myosin subfragment 1 for actin directly by fluorescence titration. The affinity of subfragment 1 for actin is increased sixfold by troponin–tropomyosin in the presence of calcium. Kinetic studies of the interaction of subfragment 1 and actin have revealed an isomerization of the actin–subfragment 1 complex from a state in which actin is weakly bound ( K a = 5.9 x 10 4 M -1 ) to a more tightly bound complex ( K a = 1.7 x 10 7 M -1 ) (Coates, Criddle & Geeves (1985) Biochem. J. 232, 351). Results in the presence of troponin–tropomyosin show the same isomerization. The sixfold increase in affinity of subfragment 1 for actin is shown to be due to a decrease in the rate of dissociation of actin from the weakly bound complex.

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The Z band in skeletal muscle in rigor exhibits the activated lattice form

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100153233 ◽

1989 ◽

Vol 47 ◽

pp. 252-253

Author(s):

R. J. Edwards

Keyword(s):

Skeletal Muscle ◽

Cross Sections ◽

Active Tension ◽

Thin Filaments ◽

Cross Bridge ◽

The Cross ◽

Cross Bridges ◽

Glycerinated Muscle

The Z band of skeletal muscle is a tetragonal array of interdigitating thin filaments from adjacent sarcomeres held together by cross connecting filaments. Two visually unique forms of the Z band (small square, ss, and basketweave, bw) can be observed by TEM of cross sections. The ss form is found in relaxed muscle and the bw is found in maximally activated muscle. The average Z spacing in the bw form is 20% largerthan in the ss form. There is a correlation between active tension and the form of the Z band. This correlation suggests that cross bridge binding in the A band is directly related to the form of the Z band. In rigor, the cross bridges are completely bound; therefore, we predicted that the Z band would exhibit the bw form. To test this hypothesis we compared unstimulated muscle to glycerinated muscle in rigor.

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Thin filaments of rabbit skeletal muscle are in helical register

Journal of Molecular Biology ◽

10.1016/0022-2836(88)90371-3 ◽

1988 ◽

Vol 204 (3) ◽

pp. 797-801 ◽

Cited By ~ 14

Author(s):

Keiko Hirose ◽

Takeyuki Wakabayashi

Keyword(s):

Skeletal Muscle ◽

Rabbit Skeletal Muscle ◽

Thin Filaments

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Calcium Induced Change in Three-Dimensional Structure of Thin Filaments of Rabbit Skeletal Muscle as Revealed by Cryoelectron Microscopy

Biochemical and Biophysical Research Communications ◽

10.1006/bbrc.1994.2274 ◽

1994 ◽

Vol 203 (2) ◽

pp. 951-958 ◽

Cited By ~ 8

Author(s):

T. Ishikawa ◽

T. Wakabayashi

Keyword(s):

Skeletal Muscle ◽

Three Dimensional ◽

Rabbit Skeletal Muscle ◽

Dimensional Structure ◽

Cryoelectron Microscopy ◽

Thin Filaments ◽

Three Dimensional Structure

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Bridgelike interconnections between thick filaments in stretched skeletal muscle fibers observed by the freeze-fracture method.

The Journal of Cell Biology ◽

10.1083/jcb.102.3.1093 ◽

1986 ◽

Vol 102 (3) ◽

pp. 1093-1098 ◽

Cited By ~ 9

Author(s):

S Suzuki ◽

G H Pollack

Keyword(s):

Skeletal Muscle ◽

Muscle Fibers ◽

Freeze Fracture ◽

Thick Filament ◽

Rapid Freezing ◽

Semitendinosus Muscle ◽

Thin Filaments ◽

Thick Filaments ◽

Cross Bridges ◽

Half Length

The ultrastructure of frog semitendinosus muscle was explored using the freeze-fracture, deep-etch, rotary-shadowing technique. Mechanically skinned fibers were stretched to decrease or eliminate the overlap of thick and thin filaments before rapid freezing with liquid propane. In relaxed, contracting, and rigor fibers, a significant number of bridgelike interconnections, distinct from those observed in the M-region, were observed between adjacent thick filaments in the non-overlap region. Their half-length and diameter corresponded approximately to the known dimensions of the cross-bridge (or myosin S-1). The interconnection may thus be formed by the binding of two apposed cross-bridges projecting from adjacent thick filaments. Fixation with 0.5% glutaraldehyde for 5-10 min before freezing effectively preserved these structures. The results indicate that the interconnections are genuine structures that appear commonly in stretched muscle fibers. They may play a role in stabilizing the thick filament lattice, and possibly in the contractile process.

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