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 o f the striated external anal sphincter (EAS) muscle have not been stud ied, even though denervation is a common etiology for fecal incontinen ce. The present study reports effects of denervation of the cat EAS an d compares them with changes in a denervated limb muscle [cat extensor digitorum longus (EDL)]. Nerves supplying the EAS and the EDL were se ctioned in anesthetized cats, which were allowed to recover and live f or 10, 30, or 60 days. Their muscles were then excised, and myofibrill ar proteins were isolated. Myosin heavy chain (MHC) isoform compositio n was measured by sodium dodecyl sulfate-polyacrylamide gel electropho resis. The EDL and EAS showed progressive increases in MHC type IIA an d progressive decreases in MHC type IIB at 10, 30, and 60 days. MHC ty pe I progressively increased in the EDL but showed no change in the EA S. We hypothesize that this distinctive transition is related to the u nique embryological origin and function of the EAS.