Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 393, Issue 1, Pages 10-26Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2009.08.009
Keywords
titin; M-band; skeletal muscle; Ca2+ sensitivity
Categories
Funding
- Dutch Organization
- German Research Foundation
- U.S. National Institutes of Health [HL062881]
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We investigated the contractile phenotype of skeletal muscle deficient in exons MEx1 and MEx2 (KO) of the titin M-band by using the cre-lox recombination system and a multidisciplinary physiological approach to study skeletal muscle contractile performance. At a maximal tetanic stimulation frequency, intact KO extensor digitorum longus muscle was able to produce wild-type levels of force. However, at submaximal stimulation frequency, force was reduced in KO mice, giving rise to a rightward shift of the force-frequency curve. This rightward shift of the force-frequency curve could not be explained by altered sarcoplasmic reticulum Ca2+ handling, as indicated by analysis of Ca2+ transients in intact myofibers and expression of Ca2+-handling proteins, but can be explained by the reduced myofilament Ca2+ sensitivity of force generation that we found. Western blotting experiments suggested that the excision of titin exons MEx1 and MEx2 did not result in major changes in expression of titin M-band binding proteins or phosphorylation level of the thin-filament regulatory proteins, but rather in a shift toward expression of slow isoforms; of the thick-filament-associated protein, myosin binding protein-C. Extraction of myosin binding protein-C from skinned muscle normalized myofilament Ca2+ sensitivity of the KO extensor digitorum longus muscle. Thus, our data suggest that the M-band region of titin affects the expression of genes involved in the regulation of skeletal muscle contraction. (C) 2009 Published by Elsevier Ltd.
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