A unique myosin isoform transition in cat striated external anal sphincter muscle induced by denervation

Denervation of limb and trunk muscles leads to characteristic changes in their biochemical properties. However, the effects of denervation of the striated external anal sphincter (EAS) muscle have not been studied, even though denervation is a common etiology for fecal incontinence. The present study reports effects of denervation of the cat EAS and compares them with changes in a denervated limb muscle [cat extensor digitorum longus (EDL)]. Nerves supplying the EAS and the EDL were sectioned in anesthetized cats, which were allowed to recover and live for 10, 30, or 60 days. Their muscles were then excised, and myofibrillar proteins were isolated. Myosin heavy chain (MHC) isoform composition was measured by sodium dodecyl sulfate- polyacrylamide gel electrophoresis. The EDL and EAS showed progressive increases in MHC type IIA and progressive decreases in MHC type IIb at 10, 30, and 60 days. MHC type I progressively increased in the EDL but showed no change in the EAS. We hypothesize that this distinctive transition is related to the unique embryological origin and function of the EAS.