Myosin Heavy Chain Composition in Human Laryngeal Muscles

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Abstract
Objectives: Myosin heavy chain (MHC) composition of human thyroarytenoid (TA), lateral cricoarytenoid (LCA), interarytenoid (IA), vocalis, posterior cricoarytenoid (PCA), and cricothyroid muscles were examined using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western bolt techniques. The presence of superfast MHC was also assessed using antibodies directed against the extraocular MHC. Study Design: MHC protein was analyzed using fresh human laryngeal muscles. Methods: Laryngeal muscles excised from cadavers were processed for SDS-PAGE. The composition of MHC isoforms was determined by densitometry. Western blot was carried out to identify specific bands. Results: MHC types IIA and IIB are the predominant MHC components in human laryngeal muscles. The adductor muscles-TA, LCA, and IA-have a higher percentage of type IIB MHC and a lower percentage of type I when compared with the abductor-PCA. The rank file order for type IIB MHC composition (TA>LCA≥IA>PCA) is the same in all specimens. A band migrating between type IIA and type I was observed in several specimens. Although similar to type IIL in rats, this atypical band did not react with antiextraocular MHC antibody on Western blot. Conclusion: Characterization of laryngeal muscles determined by the composition of MHC is correlated with function and neural input. Human laryngeal muscle is characterized by a predominance of fast-type MHCs in laryngeal closing muscle and mixed fast-slow type MHCs in respiratory and phonatory muscle groups. Although an atypical myosin band similar to type IIL (superfast) MHC in rat was identified, it did not react with anti-extraocular MHC antibody.