Voice and swallowing dysfunction as a result of recurrent laryngeal nerve
paralysis can be improved with vocal fold
injections or laryngeal framework surgery. However,
denervation atrophy can cause late-term clinical failure. A major determinant of skeletal muscle physiology is
myosin heavy chain (MyHC) expression, and previous
protein analyses have shown changes in laryngeal muscle fiber MyHC
isoform with
denervation.
RNA analyses in this setting have not been performed, and understanding
RNA levels will allow interventions better designed to reverse processes such as
denervation in the future. Total
RNA was extracted from bilateral rat thyroarytenoid (TA), posterior cricoarytenoid (PCA), and cricothyroid (CT) muscles in rats. Primers were designed using published MyHC
isoform sequences.
SYBR Green real-time reverse transcription-polymerase chain reaction (SYBR-RT-PCR) was used for quantification. The electropherogram showed a clear separation of total
RNA to 28S and 18S subunits. Melting curves illustrated single peaks for all type MyHC primers. All MyHC
isoforms were identified in all muscles with various degrees of expression. Quantitative PCR is a sensitive method to detect MyHC
isoforms in laryngeal muscle.
Isoform expression using
mRNA analysis was similar to previous analyses but showed some important differences. This technique can be used to quantitatively assess response to interventions targeted to maintain muscle bulk after
denervation.
LEARNING OUTCOMES: (1) Readers will be able to describe the relationship between
myosin heavy chain expression and muscle contractile properties. (2) Readers will be able to separate
myosin heavy chain isoforms into slow and fast twitch phenotypes. (3) Readers will be able to describe differential muscle
isoform expression between different laryngeal muscles. (4) Readers will be able to compare this study to other modalities of determining muscle fiber type.