title: Adult human upper esophageal sphincter contains specialized muscle fibers expressing unusual myosin heavy chain isoforms.
abstract: The functional upper esophageal sphincter (UES) is composed of the cricopharyngeus muscle (CP), the most inferior part of the inferior pharyngeal constrictor (iIPC), and the upper esophagus (UE). This sphincter is collapsed and exhibits sustained muscle activity in the resting state; it only relaxes and opens during swallowing, vomiting, and belching. The tonic contractile properties of the UES suggest that the skeletal muscle fibers in this sphincter differ from those in the limb and trunk muscles. In this study, myosin heavy chain (MHC) composition in the adult human UES muscles obtained from autopsies was investigated using immunocytochemical and immunoblotting techniques. Results showed that the adult human UES muscle fibers expressed unusual MHC isoforms such as slow-tonic (MHC-ton), alpha-cardiac (MHC-alpha), neonatal (MHC-neo), and embryonic (MHC-emb), which coexisted with the major MHCs (i.e., MHCI, IIa, and IIx). MHC-ton and MHC-alpha were coexpressed predominantly with slow-type I MHC isoform, whereas MHC-neo and MHC-emb coexisted mainly with fast-type IIa MHC. A slow inner layer (SIL) and a fast outer layer (FOL) in the iIPC and CP were identified immunocytochemically. MHC-ton- and MHC-alpha-containing fibers were concentrated mainly in the SIL, whereas MHC-neo- and MHC-emb-containing fibers were distributed primarily to the FOL. Identification of the specialized muscle fibers and their distribution patterns in the adult human UES is valuable for a better understanding of the physiological and pathophysiological behaviors of the sphincter.
authors.affiliation: Upper Airway Research Laboratory, Department of Otolaryngology, The Mount Sinai School of Medicine, New York, NY 10029-6574, USA. lmu03@yahoo.com
authors.forename: Liancai
authors.initials: L
authors.lastname: Mu
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.forename: Hungxi
authors.initials: H
authors.lastname: Su
authors.forename: Ira
authors.initials: I
authors.lastname: Sanders
mesh_terms: D000328:Adult; D049631:Esophageal Sphincter, Upper / Q000378:metabolism*; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D018995:Myosin Heavy Chains