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Sugi H, Iwamoto H, Akimoto T, et al. Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP. Proc Natl Acad Sci U S A. 1998;95(5):2273-8doi: 10.1073/pnas.95.5.2273.
Sugi, H., Iwamoto, H., Akimoto, T., & Ushitani, H. (1998). Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP. Proceedings of the National Academy of Sciences of the United States of America, 95(5), 2273-8. https://doi.org/10.1073/pnas.95.5.2273
Sugi, H, et al. "Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP." Proceedings of the National Academy of Sciences of the United States of America vol. 95,5 (1998): 2273-8. doi: https://doi.org/10.1073/pnas.95.5.2273
Sugi H, Iwamoto H, Akimoto T, Ushitani H. Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP. Proc Natl Acad Sci U S A. 1998 Mar 03;95(5):2273-8. doi: 10.1073/pnas.95.5.2273. PMID: 9482875; PMCID: PMC19317.
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Proc Natl Acad Sci U S A. 1998 Mar 03;95(5):2273-8. doi: 10.1073/pnas.95.5.2273.

Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP.

Proceedings of the National Academy of Sciences of the United States of America

H Sugi, H Iwamoto, T Akimoto, H Ushitani

Affiliations

  1. Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173, Japan. [email protected]

PMID: 9482875 PMCID: PMC19317 DOI: 10.1073/pnas.95.5.2273
Free PMC Article

Abstract

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, after laser-flash photolysis of caged calcium. Immediately before laser-flash activation, almost all of the myosin heads in the fiber are in the state M.ADP.Pi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force, and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of M.ADP.Pi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemomechanical energy conversion in individual myosin heads changes in a load-dependent manner.

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