Large-scale Models Reveal the Two-component Mechanics of Striated Muscle

Abstract

This paper provides a comprehensive explanation of striated muscle mechanics and contraction on the basis of filament rotations. Helical proteins, particularly the coiled-coils of tropomyosin, myosin and α-actinin, shorten their H-bonds cooperatively and produce torque and filament rotations when the Coulombic net-charge repulsion of their highly charged side-chains is diminished by interaction with ions. The classical "two-component model" of active muscle differentiated a "contractile component" which stretches the "series elastic component" during force production. The contractile components are the helically shaped thin filaments of muscle that shorten the sarcomeres by clockwise drilling into the myosin cross-bridges with torque decrease (= force-deficit). Muscle stretch means drawing out the thin filament helices off the cross-bridges under passive counterclockwise rotation with torque increase (= stretch activation). Since each thin filament is anchored by four elastic α-actinin Z-filaments (provided with forceregulating sites for Ca 2+ binding), the thin filament rotations change the torsional twist of the four Z-filaments as the "series elastic components". Large scale models simulate the changes of structure and force in the Z-band by the different Z-filament twisting stages A, B, C, D, E, F and G. Stage D corresponds to the isometric state. The basic phenomena of muscle physiology, i. e. latency relaxation, Fenn-effect, the force-velocity relation, the length-tension relation, unexplained energy, shortening heat, the Huxley-Simmons phases, etc. are explained and interpreted with the help of the model experiments.

Nanoscopic changes in the lattice structure of striated muscle sarcomeres involved in the mechanism of spontaneous oscillatory contraction (SPOC)

“…For example, an in vitro motility assay demonstrated that actin filaments gliding over a myosin-coated coverslip surface can rotate around their long axis 61,62 and form a superhelix 63 . Also, the actin filament can undergo a rolling sliding motion in sarcomeres 64,65 . The torque may cause the generation of torsion in the myofilaments as sarcomeres contract.…”

The Different Muscle-Energetics during Shortening and Stretch

“…A series of steps should produce more friction since the redeveloped force after each quick release depends on additional internal rotation during rewinding the Z-filaments [2]. …”

Effect of heat and cold on tendon flexibility and force to flex the human knee

“…Heat also increases glycogen resynthesis and muscle recovery [10]. Heat is also cited as increasing flexibility and thus reducing the chance of injury, and reducing energy cost of muscle contraction by reducing internal friction [11,12]. Internal energy costs are reduced by warming muscle, but many of these studies have been done in animals and very few in humans.…”

“…The response of stretch receptors in the cat are also increased by heat [15]. The mechanism of the changes in the series’ elastic component is partly due to unwinding of the actin filaments in muscle due to stretch and partly due to collagen relaxation [11,12]. There is also rotation of the actin filaments with heat [11].…”

“…The mechanism of the changes in the series’ elastic component is partly due to unwinding of the actin filaments in muscle due to stretch and partly due to collagen relaxation [11,12]. There is also rotation of the actin filaments with heat [11]. While there is some evidence that heat increases muscle flexibility in humans, there has been no study of where the benefit is (parallel or series elastic components, or how long the benefit lasts) [16–19].…”