Evidence against the Swinging Lever Arm Mechanism in Muscle Contraction Based on the Effect of Antibodies to Myosin Head

2016 ◽  
Vol 7 (3) ◽  
Author(s):  
Sugi H ◽  
Chaen S
Keyword(s):  
Muscle Contraction ◽  
Myosin Head ◽  
Lever Arm

scholarly journals X-ray Diffraction Studies on the Structural Origin of Dynamic Tension Recovery Following Ramp-Shaped Releases in High-Ca Rigor Muscle Fibers

2020 ◽  
Vol 21 (4) ◽  
pp. 1244
Author(s):  
Haruo Sugi ◽  
Maki Yamaguchi ◽  
Tetsuo Ohno ◽  
Hiroshi Okuyama ◽  
Naoto Yagi
Keyword(s):  
Muscle Contraction ◽  
Actin Filaments ◽  
Myosin Head ◽  
Muscle Fibers ◽  
Skinned Fibers ◽  
Myosin Filament ◽  
X Ray Diffraction ◽  
X Ray ◽  
Tension Recovery ◽  
Pass Through

It is generally believed that during muscle contraction, myosin heads (M) extending from myosin filament attaches to actin filaments (A) to perform power stroke, associated with the reaction, A-M-ADP-Pi → A-M + ADP + Pi, so that myosin heads pass through the state of A-M, i.e., rigor A-M complex. We have, however, recently found that: (1) an antibody to myosin head, completely covering actin-binding sites in myosin head, has no effect on Ca2+-activated tension in skinned muscle fibers; (2) skinned fibers exhibit distinct tension recovery following ramp-shaped releases (amplitude, 0.5% of Lo; complete in 5 ms); and (3) EDTA, chelating Mg ions, eliminate the tension recovery in low-Ca rigor fibers but not in high-Ca rigor fibers. These results suggest that A-M-ADP myosin heads in high-Ca rigor fibers have dynamic properties to produce the tension recovery following ramp-shaped releases, and that myosin heads do not pass through rigor A-M complex configuration during muscle contraction. To obtain information about the structural changes in A-M-ADP myosin heads during the tension recovery, we performed X-ray diffraction studies on high-Ca rigor skinned fibers subjected to ramp-shaped releases. X-ray diffraction patterns of the fibers were recorded before and after application of ramp-shaped releases. The results obtained indicate that during the initial drop in rigor tension coincident with the applied release, rigor myosin heads take up applied displacement by tilting from oblique to perpendicular configuration to myofilaments, and after the release myosin heads appear to rotate around the helical structure of actin filaments to produce the tension recovery.

scholarly journals The swinging lever-arm hypothesis of muscle contraction

1997 ◽  
Vol 7 (2) ◽  
pp. R112-R118 ◽  
Author(s):  
Kenneth C Holmes
Keyword(s):  
Muscle Contraction ◽  
Lever Arm

scholarly journals Definite Difference Between In Vitro Actin-Myosin Sliding and Muscle Contraction Revealed by the Effect of Antibody to Myosin Head Converter Domain

2012 ◽  
Vol 102 (3) ◽  
pp. 146a
Author(s):  
Haruo Sugi ◽  
Takakazu Kobayashi ◽  
Shigeru Chaen ◽  
Takuya Miyakawa ◽  
Masaru Tanokura ◽  
...  
Keyword(s):  
Muscle Contraction ◽  
Myosin Head ◽  
Definite Difference

scholarly journals Mechanical model of muscle contraction. 1. Force-velocity relationship

2019 ◽  
Author(s):  
S. Louvet
Keyword(s):  
Muscle Contraction ◽  
Mechanical Characteristics ◽  
Myosin Head ◽  
Myosin Ii ◽  
Additional Term ◽  
Linear Displacement ◽  
Skeletal Muscle Fiber ◽  
Velocity Relationship ◽  
Force Velocity ◽  
Two Parameters

AbstractThe two parameters that determine the functionality of a skeletal muscle fiber are the tension (T) exerted at its two endpoints and the shortening speed (V), two mechanical characteristics. We established a relationship between T and V by developing a theoretical model of muscle contraction based on the swinging lever arm hypothesis. At the nanoscale, force and movement are generated by the myosin II heads during the working stroke (WS). The change in conformation of a myosin head during the WS is characterized by the rotation of the lever correlated to the linear displacement of the motor domain. The position of the lever is marked by the angle θ. The maximum variation of θ between the two limits θup and θdown relating to the two positions up and down is usually given equal to 70°. When the angle θ is between θup and θdown, the WS is triggered in three modes, fast, slow or very slow. During the isometric tetanus plateau, θ is uniformly distributed between the two angles θup and θT separated by a usual difference of 50°. Consequently during isometric tetanus plateau there is a 20° interval between θT and θdown where no head is found in WS. We link this absence to the slow detachment of the heads whose orientation of the levers is between θT and θdown during the rise to the isometric tetanus plateau. The equation between T and V refers to these four occurrences: fast, slow or very slow initiations of the WS between θup and θdown, then slow detachment between θT and θdown. The equation is constructed from the geometric data of the myosin head and the time constants of the cross-bridge cycle reactions associated with these four events. The biphasic aspect of the curve is explained by the slow detachment that occurs only at very slow speeds. An additional term, derived from the viscosity present as soon as the velocity increases completes the equation. An adequate fit between the model and examples from the physiological literature is found (r2 > 99%).

scholarly journals Muscle contraction as a Markov Process - II: x-ray interference data (M3 & M6 reflections) imply myosin cross-bridge motions are controlled by structural transitions along actin filaments

2021 ◽  
Author(s):  
Clarence E Schutt ◽  
Vladimir Gelfand ◽  
Eli Paster
Keyword(s):  
Muscle Contraction ◽  
Actin Filaments ◽  
Myosin Head ◽  
Muscle Fibers ◽  
Head Movements ◽  
Published Data ◽  
Structural Transitions ◽  
X Ray ◽  
Thick Filaments ◽  
In Series

AbstractThe unit underlying the construction and functioning of muscle fibers is the sarcomere. Tension develops in fibers as thousands of sarcomeres arranged in series contract in unison. Shortening is due to the sliding of actin thin filaments along antiparallel arrays of myosin thick filaments. Remarkably, myosin catalytic heads situated across the center M-line of a sarcomere are separated by a distance that is a half integral of the 14.5 nm spacing between successive layers of myosin heads on the thick filaments. This results in the splitting of the 14.5 nm meridional reflection in X-ray diffraction patterns of muscle fibers. Following a quick drop in tension, changes in the relative intensities of the split meridional peaks provide a sensitive measure of myosin head movements. We use published data obtained with the x-ray interference method to validate a theory of muscle contraction in which cooperative structural transitions along force-generating actin filaments regulate the binding of myosin heads. The probability that an actin-bound myosin head will detach is represented here by a statistical function that yields a length-tension curve consistent with classical descriptions of the recovery of contracting muscle fibers subjected to millisecond drops in tension.

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