Myosin heavy chain isoforms in adult equine skeletal muscle: An immunohistochemical and electrophoretic study

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Abstract
Background The aim of this study was to characterize the myosin heavy chain (MyHC) isoforms present in equine skeletal muscle. Methods Muscle biopsies were removed from the superficial region of the gluteus medius muscle of five mature horses and analyzed by immunohistochemistry (using a battery of monoclonal antibodies specific for rat MyHC isoforms) and sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Results Immunohistochemistry allowed subdivision of three different muscle fiber populations containing a single MyHC, one slow and two fast, and two hybrid populations, one containing slow and fast MyHCs and another with both fast‐MyHC isoforms. Electrophoresis of MyHC confirmed the existence of three resolvable bands, with an electrophoretic mobility parallel to type I, IIa, and IIx rat MyHCs. The identities of two of these MyHCs were easily comparable with slow type I and fast type IIa MyHCs from rat skeletal muscle. However, a precise identification of the second fast MyHC was not made. Conclusions These results show the presence of three different MyHC isoforms in mature equine skeletal muscle, whose differential distribution defines three fiber types containing a single MyHC and two hybrid fiber populations containing either both slow and fast type IIa MyHCs or both fast MyHC isoforms.