Abstract
Loading of extracted muscle fibers causes a small, sudden lengthening, followed by a slower, plastic extension, which is reversed only by active contraction. Polyphosphates in the presence of Mg strongly accelerate plastic extension, but elastic changes in length remain the same as during rigor. The modulus of elasticity on the average is about 6.2 x 107 dynes per cm.2 This value is about 40 times larger than that of rubber, if compared on a water-free basis. Extension of muscle, therefore, is almost entirely due to plastic deformation. Mg is essential for the softening action of adenosinetriphosphate (ATP) and can produce partial relaxation in the absence of a relaxation factor. After partial removal of bound Mg, ATP causes strong contraction, but only slight softening. The same condition is produced by very low concentrations of ATP in the presence of phosphocreatine. These observations show that during contraction passive mechanical properties may remain essentially like those during rigor. The constancy of elastic extensibility distinguishes contraction produced by ATP from contraction induced by non-specific agents in various fibrous structures and caused by an increase in configurational entropy.
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Selected References
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- AUBERT X. Intervention d'un élément élastique pur dans la contraction du muscle strié. Arch Int Physiol Biochim. 1955 Jun;63(2):197–202. doi: 10.3109/13813455509150407. [DOI] [PubMed] [Google Scholar]
- BENDALL J. R. Further observations on a factor (The `Marsh' factor) effecting relaxation of ATP-shortened muscle-fibre models and the effect of Ca and Mg ions upon it. J Physiol. 1953 Aug;121(2):232–254. doi: 10.1113/jphysiol.1953.sp004944. [DOI] [PMC free article] [PubMed] [Google Scholar]
- BOZLER E. Binding of calcium and magnesium by the contractile elements. J Gen Physiol. 1955 Jul 20;38(6):735–742. doi: 10.1085/jgp.38.6.735. [DOI] [PMC free article] [PubMed] [Google Scholar]
- BOZLER E. Evidence of an ATP-actomyosin complex in relaxed muscle and its response to calcium ions. Am J Physiol. 1952 Mar;168(3):760–765. doi: 10.1152/ajplegacy.1952.168.3.760. [DOI] [PubMed] [Google Scholar]
- BOZLER E. Plasticity of contractile elements of muscle as studies in extracted muscle fibers. Am J Physiol. 1952 Nov;171(2):359–364. doi: 10.1152/ajplegacy.1952.171.2.359. [DOI] [PubMed] [Google Scholar]
- BOZLER E. Relaxation in extracted muscle fibers. J Gen Physiol. 1954 Nov 20;38(2):149–159. doi: 10.1085/jgp.38.2.149. [DOI] [PMC free article] [PubMed] [Google Scholar]
- LAKI K., BOWEN W. J. The contraction of muscle fiber and myosin B thread in KI and KSCN solutions. Biochim Biophys Acta. 1955 Feb;16(2):301–302. doi: 10.1016/0006-3002(55)90227-4. [DOI] [PubMed] [Google Scholar]
- LORAND L. Adenosine triphosphate-creatine transphosphorylase as relaxing factor of muscle. Nature. 1953 Dec 26;172(4391):1181–1183. doi: 10.1038/1721181a0. [DOI] [PubMed] [Google Scholar]
- SZENT-GYORGYI A. Free-energy relations and contraction of actomyosin. Biol Bull. 1949 Apr;96(2):140–161. [PubMed] [Google Scholar]