The active and passive contractile performance of skeletal muscle fibers largely depends on the myosin heavy chain (MHC) isoform and the stiffness of the titin spring, respectively. Open questions concern the relationship between titin-based stiffness and active contractile parameters, and titin's importance for total passive muscle stiffness. Here, a large set of adult rabbit muscles (n = 37) was studied for titin size diversity, passive mechanical properties, and possible correlations with the fiber/MHC composition. Titin isoform analyses showed sizes between ∼3300 and 3700 kD; 31 muscles contained a single isoform, six muscles coexpressed two isoforms, including the psoas, where individual fibers expressed similar isoform ratios of 30:70 (3.4:3.3 MD). Gel electrophoresis and Western blotting of two other giant muscle proteins, nebulin and obscurin, demonstrated muscle type–dependent size differences of ≤70 kD. Single fiber and single myofibril mechanics performed on a subset of muscles showed inverse relationships between titin size and titin-borne tension. Force measurements on muscle strips suggested that titin-based stiffness is not correlated with total passive stiffness, which is largely determined also by extramyofibrillar structures, particularly collagen. Some muscles have low titin-based stiffness but high total passive stiffness, whereas the opposite is true for other muscles. Plots of titin size versus percentage of fiber type or MHC isoform (I-IIB-IIA-IID) determined by myofibrillar ATPase staining and gel electrophoresis revealed modest correlations with the type I fiber and MHC-I proportions. No relationships were found with the proportions of the different type II fiber/MHC-II subtypes. Titin-based stiffness decreased with the slow fiber/MHC percentage, whereas neither extramyofibrillar nor total passive stiffness depended on the fiber/MHC composition. In conclusion, a low correlation exists between the active and passive mechanical properties of skeletal muscle fibers. Slow muscles usually express long titin(s), predominantly fast muscles can express either short or long titin(s), giving rise to low titin-based stiffness in slow muscles and highly variable stiffness in fast muscles. Titin contributes substantially to total passive stiffness, but this contribution varies greatly among muscles.
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1 November 2005
Article|
October 17 2005
Isoform Diversity of Giant Proteins in Relation to Passive and Active Contractile Properties of Rabbit Skeletal Muscles
Lucas G. Prado,
Lucas G. Prado
1Institute of Physiology and Pathophysiology, University of Heidelberg, D-69120 Heidelberg, Germany
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Irina Makarenko,
Irina Makarenko
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
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Christian Andresen,
Christian Andresen
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
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Martina Krüger,
Martina Krüger
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
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Christiane A. Opitz,
Christiane A. Opitz
1Institute of Physiology and Pathophysiology, University of Heidelberg, D-69120 Heidelberg, Germany
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Wolfgang A. Linke
Wolfgang A. Linke
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
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Lucas G. Prado
1Institute of Physiology and Pathophysiology, University of Heidelberg, D-69120 Heidelberg, Germany
Irina Makarenko
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
Christian Andresen
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
Martina Krüger
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
Christiane A. Opitz
1Institute of Physiology and Pathophysiology, University of Heidelberg, D-69120 Heidelberg, Germany
Wolfgang A. Linke
2Physiology and Biophysics Unit, University of Muenster, D-48149 Muenster, Germany
Correspondence to Wolfgang A. Linke: [email protected]
L.G. Prado and I. Makarenko contributed equally to this work.
Abbreviations used in this paper: BDM, 2,3-butanedione monoxime; MHC, myosin heavy chain; PT, passive tension; SL, sarcomere length.
Received:
July 13 2005
Accepted:
September 26 2005
Online ISSN: 1540-7748
Print ISSN: 0022-1295
The Rockefeller University Press
2005
J Gen Physiol (2005) 126 (5): 461–480.
Article history
Received:
July 13 2005
Accepted:
September 26 2005
Citation
Lucas G. Prado, Irina Makarenko, Christian Andresen, Martina Krüger, Christiane A. Opitz, Wolfgang A. Linke; Isoform Diversity of Giant Proteins in Relation to Passive and Active Contractile Properties of Rabbit Skeletal Muscles . J Gen Physiol 1 November 2005; 126 (5): 461–480. doi: https://doi.org/10.1085/jgp.200509364
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