MYOSIN HEAVY-CHAIN ISOFORMS IN ADULT EQUINE SKELETAL-MUSCLE - AN IMMUNOHISTOCHEMICAL AND ELECTROPHORETIC STUDY

Background: The aim of this study was to characterize the myosin heavy chain (MyHC) isoforms present in equine skeletal muscle. Methods: Mus cle biopsies were removed from the superficial region of the gluteus m edius muscle of five mature horses and analyzed by immunohistochemistr y (using a battery of monoclonal antibodies specific for rat MyHC isof orms) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. R esults: Immunohistochemistry allowed subdivision of three different mu scle fiber populations containing a single MyHC, one slow and two fast , and two hybrid populations, one containing slow and fast MyHCs and a nother with both fast-MyHC isoforms. Electrophoresis of MyHC confirmed the existence of three resolvable bands, with an electrophoretic mobi lity 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 skeleta l muscle, whose differential distribution defines three fiber types co ntaining a single MyHC and two hybrid fiber populations containing eit her both slow and fast type IIa MyHCs or both fast MyHC isoforms. (C) 1996 Wiley-Liss, Inc.