A new concept in laryngeal muscle: multiple myosin isoform types in single muscle fibers of the lateral cricoarytenoid.

This report describes the first known investigation of canine laryngeal muscle in which single fibers were dissected and their myosin heavy chain (MHC) isoform content was analyzed. Both SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and western blot techniques were used. The data from single fiber SDS-PAGE indicate that the lateral cricoarytenoid (LCA) is predominantly a fast muscle composed of the following MHC isoforms: Type I, 16.3%; Type IIA, 71.3%; Type IIX, 10.4%; and Type IIB, 2.0%. The results reveal a phenomenon that, to our knowledge, has not been previously described for laryngeal muscle: the presence of two or more MHC isoforms in a single canine LCA muscle fiber. A large number (41%) of muscle fibers coexpressed two or more MHC isoforms. The three most common patterns of coexpression were Type IIA/IIX (72%), Type IIA/I (16%), and Type IIA/IIX/I (8%). Interestingly, the fast Type IIX MHC isoform was typically present with other isoforms and rarely found by itself in individual fibers. Additional experiments are underway to determine whether other laryngeal muscles exhibit such an unusually high ratio of MHC isoform polymorphism.