Super-relaxed state of myosin in human skeletal muscle is fiber-type dependent

Lien A. Phung, Aurora D. Foster, Mark S. Miller, Dawn A. Lowe, David D. Thomas

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The myosin super-relaxed state (SRX) in skeletal muscle is hypothesized to play an important role in regulating muscle contractility and thermogenesis in humans but has only been examined in model organisms. Here we report the first human skeletal muscle SRX measurements, using quantitative epifluorescence microscopy of fluorescent 20/30-O-(N-meth-ylanthraniloyl) ATP (mantATP) single-nucleotide turnover. Myosin heavy chain (MHC) isoform expression was determined using gel electrophoresis for each permeabilized vastus lateralis fiber, to allow for novel comparisons of SRX between fiber types. We find that the fraction of myosin in SRX is less in MHC IIA fibers than in MHC I and IIAX fibers (P = 0.008). ATP turnover of SRX is faster in MHC IIAX fibers compared with MHC I and IIA fibers (P = 0.001). We conclude that SRX biochemistry is measurable in human skeletal muscle, and our data indicate that SRX depends on fiber type as classified by MHC isoform. Extension from this preliminary work would provide further understanding regarding the role of SRX in human muscle physiology.

Original languageEnglish (US)
Pages (from-to)C1158-C1162
JournalAmerican Journal of Physiology - Cell Physiology
Issue number6
StatePublished - Dec 2020

Bibliographical note

Publisher Copyright:
Copyright © 2020 the American Physiological Society


  • ATPase
  • Epifluorescence microscopy
  • MantATP
  • Myosin heavy chain (MHC)
  • SRX

PubMed: MeSH publication types

  • Journal Article
  • Research Support, N.I.H., Extramural


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