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Keywords:

  • human;
  • myosin heavy chain;
  • muscle;
  • suprahyoid;
  • swallowing

ABSTRACT

Introduction: Contradictory reports of the myosin heavy chain (MHC) composition of adult human suprahyoid muscles leave unresolved the extent to which these muscles express developmental and unconventional MHC. Methods: By immunohistochemistry, separation sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)-Coomassie, separation SDS-PAGE-Western blot, and mRNA PCR, we tested for conventional MHCI, MHCIIA, MHCIIX, developmental MHC embryonic and MHC neonatal, and unconventional MHC alpha-cardiac, MHC extraocular, and MHC slow tonic in adult human anterior digastric (AD), geniohyoid (GH), and mylohyoid (MH) muscles. Results: By separation SDS-PAGE-Coomassie and Western blot, only conventional MHC are present. By immunohistochemistry all muscle fibers are positive for MHCI, MHCIIA, or MHCIIX, and fewer than 4 fibers/mm2 are positive for developmental or unconventional MHC. By PCR, mRNA of MHCI and MHCIIA dominate, with sporadically detectable MHC alpha-cardiac and without detectable mRNA of other developmental and unconventional MHC. Conclusions: We conclude that human suprahyoid muscles AD, GH, and MH are composed almost exclusively of conventional MHC isoforms. Muscle Nerve 49:534–544, 2014