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Three Dimensional Compartmentalization of Myosin Heavy Chain Isoforms in the Human Thyroarytenoid Muscle
Author(s) -
Matrka Laura A.,
Reiser Peter J.,
Forrest L. Arick,
deSilva Brad W.
Publication year - 2010
Publication title -
the laryngoscope
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.181
H-Index - 148
eISSN - 1531-4995
pISSN - 0023-852X
DOI - 10.1002/lary.21246
Subject(s) - library science , citation , state (computer science) , medicine , computer science , algorithm
Educational Objective: At the conclusion of this presentation, the participants should be able to 1) Discuss the variability in myosin content throughout various compartments of the human thyroarytenoid muscle 2) Understand the range of myosin heavy chain isoforms present in the muscle 3) Explain the variability in fatigue resistance, power and muscle-shortening velocity among different isoforms and 4) Compare this range of isoforms to that present in other muscle types and in other mammals Objectives: Myosin heavy chain (MHC) is the primary determinant of muscle-shortening velocity in muscle fibers. Isoforms include MCH-I, II-A, II-D, and II-B, in order of increasing velocity and power. Previous animal work has demonstrated a wide and compartmentalized range of MHC isoforms in the thyroarytenoid muscle, consistent with its multiple functions of phonation, respiration, and airway protection. This study seeks to elucidate the detailed pattern of MHC isoforms in the human thyroarytenoid muscle. Study Design: Basic science research Methods: Five longitudinally-oriented specimens from fresh cadaveric thyroarytenoid muscle were obtained from medial to lateral (ML1-ML5) at the midline of the cord. Another five specimens were obtained from superior to inferior at both the medial edge (M1-M5) and the lateral edge (L1-L5) of the thyroarytenoid muscle. Specimens were weighed, prepared for gel electrophoresis, and analyzed for total MHC content and percentage of each isoform. Results: Total MHC content varied markedly between medial and lateral compartments, with highest myosin content laterally. Within both medial and lateral compartments there was a higher MHC-IID content superiorly. MHC-IIA was the predominant isoform, comprising 60-70% of MHC content. MHC-I was present overall at a higher percentage than in other mammals. Conclusions: The high level of MHC laterally was striking. We therefore hypothesize that greater force is generated laterally, farthest from the vocal ligament. Furthermore, the isoforms associated with slower contraction velocities and increased fatigue resistance, MHC-IIA and MHC-I, predominated in the human samples compared to the dog.