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Geometrical Conditions Indispensable for Muscle Contraction
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Int. J. Mol. Sci. 2011, 12(5), 2891-2900;

The Different Muscle-Energetics during Shortening and Stretch

Formerly Institute of Plant Physiology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria
Received: 21 February 2011 / Revised: 17 March 2011 / Accepted: 12 April 2011 / Published: 3 May 2011
(This article belongs to the Special Issue Advances in Muscle Contraction Studies)
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The helical shape of the thin filaments causes their passive counterclockwise rotation during muscle stretch that increases tensile stress and torque at first by unwinding and then by winding up the four anchoring Z-filaments. This means storage of energy in the series elastic Z-filaments and a considerable decrease of the liberated energy of heat and work to (h—wap), where h is the heat energy and wap the stretch energy induced from outside by an apparatus. The steep thin filament helix with an inclination angle of 70° promotes the passive rotation during stretch, but impedes the smooth sliding of shortening by increased friction and production of frictional heat. The frictional heat may be produced by the contact with the myosin cross-bridges: (1) when they passively snap on drilling thin filaments from cleft to cleft over a distance 2 × 2.7 nm = 5.4 nm between the globular actin monomers in one groove, causing stepwise motion; or (2) when they passively cycle from one helical groove to the next (distance 36 nm). The latter causes more heat and may take place on rotating thin filaments without an effective forward drilling (“idle rotation”), e.g., when they produce “unexplained heat” at the beginning of an isometric tetanus. In an Appendix to this paper the different states of muscle are defined. The function of its most important components is described and rotation model and power-stroke model of muscular contraction is compared. View Full-Text
Keywords: active and passive thin filament-rotation; frictional heat active and passive thin filament-rotation; frictional heat
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Jarosch, R. The Different Muscle-Energetics during Shortening and Stretch. Int. J. Mol. Sci. 2011, 12, 2891-2900.

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