Open AccessSuper-relaxed state of myosin in human skeletal muscle is fiber-type dependent
Author(s) -
Lien A. Phung,
Aurora D. Foster,
Mark S. Miller,
Dawn A. Lowe,
David D. Thomas
Publication year - 2020
Publication title -
american journal of physiology. cell physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.432
H-Index - 181
eISSN - 1522-1563
pISSN - 0363-6143
DOI - 10.1152/ajpcell.00396.2020
Subject(s) - myosin , skeletal muscle , biology , skeletal muscle fibers , major histocompatibility complex , contractility , gene isoform , microbiology and biotechnology , biochemistry , anatomy , endocrinology , gene
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 2'/3'- O -( N -methylanthraniloyl) 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.