Myosin heavy chain composition in rat laryngeal muscles after denervation

The effects of denervation on myosin heavy chain (MHC) expression in specific laryngeal muscles are characterized using gel electrophoresis. Observed temporal changes in MHC composition will then be used as a biologic marker in studies designed to develop strategies for laryngeal reinnervation and gene therapy. Animal study using an adult rat model for laryngeal paralysis. In anesthetized rats the left recurrent and superior laryngeal nerve were divided. Animals were survived for 7, 14, 28, 90, and 180 days. Animals were euthanized and the thyroarytenoid (TA), vocalis (VOC), posterior cricoarytenoid (PCA), lateral cricoarytenoid (LCA), and cricothyroid (CT) muscle excised. Each muscle was processed for sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and densitometric measurements were obtained to determine composition of MHC fiber types. The changes in relative MHC composition are described for each specific laryngeal muscle. In general, a decrease in type IIB and an increase in IIA and IIX are seen after denervation. Expression of IIL in the denervated condition is variable and the relative change in type I is minimal. This study supports previous work using rat soleus muscle in which IIA/IIX expression is favored in conditions with decreased neuromuscular activity, and conversely, IIB expression is activity dependent. Expression of type I appears to be independent of neural activity. Further study will be undertaken to quantify expression of MHC components and to study factors modulating expression.