Differential isoform expression of SERCA and myosin heavy chain in hypopharyngeal muscles
Composition of slow, fast and hybrid fibres of pharyngeal muscles, associated with pharyngeal movements and regulation, has been rarely studied. The present study aimed to identify expression of sarcoplasmic reticulum Ca2+ ATPase (SERCA) and myosin heavy chain (MHC) and hybrid isoforms in different pharyngeal muscles of young and aged rats as well as human. Isoform expression profiles of SERCA, MHC and hybrid isoforms among six components of pharyngeal muscle were immunohistochemically evaluated in rat and human. The result showed that pharyngeal muscles predominantly expressed fast fibres (SERCA1 and MHCII), whereas expression of slow fibres (SERCA2 and MHCI) was low, but different depending on muscle components. Inner layer of pharyngeal muscles expressed more SERCA2 and hybrid fibres than the outer layer. Pharyngeal muscles in aged rats showed increased hybrid fibers and SERCA2. Human thyropharyngeus also showed a higher portion of fast fibres compared to cricopharyngeus. Thus, in contrast to abundance of fast fibres, slow and hybrid fibres are differentially expressed depending on muscle components and layers as well as aging. These results lead to further understanding of coordinated regulation for speech and swallowing. The unique data presented in this study on SERCA isoform expressions in both rats and humans suggest an ability to handle calcium changes according functional demands.