Skeletal Muscle Changes in Hypothyroidism

Carlos Bernardo Mantilla, Douglas E. Dow, Gary C Sieck

Research output: Chapter in Book/Report/Conference proceedingChapter

2 Scopus citations

Abstract

This chapter reviews hypothyroidism-induced structural and functional plasticity of motor units. Iodine deficiency and other alterations in iodine metabolism can lead to hypothyroidism. Motor unit and muscle fiber type classification is critical when considering plasticity. With hypothyroidism, motoneurons display decreased soma and axon diameter, which may increase their excitability and reduce conduction velocity. Neuromuscular junctions at type I and IIa fibers display reduced size and complexity (classification based on myosin heavy chain (MHC) expression), which improves their ability to maintain neuromuscular transmission. The cross-sectional area (CSA) of type I and IIa fibers is either maintained or increased, whereas that of type IIx and/or type IIb fibers decreases. Expression of MHC isoforms is altered in hypothyroid muscles, with increased expression of MHCΣλοφ and reduced expression of MHC-X and MHC-B. In fact, MHC content per half-sarcomere decreases at fibers expressing MHC-X and/or MHC-B, reflecting fewer myosin cross-bridges available for force generation. Taken together, these changes result in reduced maximum force. The force generated per myosin cross-bridge is maintained, indicating that hypothyroidism does not impair cross-bridge force generation. Across fiber types, myosin cross-bridge cycling rates are reduced, as reflected by the markedly slower maximum velocity of shortening, rate constant for force redevelopment and ATP consumption rates.

Original languageEnglish (US)
Title of host publicationComprehensive Handbook of Iodine
PublisherElsevier Inc.
Pages1087-1101
Number of pages15
ISBN (Print)9780123741356
DOIs
StatePublished - 2009

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ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)

Cite this

Mantilla, C. B., Dow, D. E., & Sieck, G. C. (2009). Skeletal Muscle Changes in Hypothyroidism. In Comprehensive Handbook of Iodine (pp. 1087-1101). Elsevier Inc.. https://doi.org/10.1016/B978-0-12-374135-6.00111-4