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 laryngea l 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 cricoaryteno id (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 II B, 2.0%, The results reveal a phenomenon that, to our knowledge, has n ot been previously described for laryngeal muscle: the presence of two or more MHC isoforms in a single canine LCA muscle fiber, A large num ber (41%) of muscle fibers coexpressed two or more MHC isoforms, The t hree most common patterns of coexpression were Type IIA/IIX (72%), Typ e IIA/I (16%), and Type IIA/IIX/I (8%), Interestingly, the fast Type I IX MHC isoform was typically present with other isoforms and rarely fo und by itself in individual fibers. Additional experiments are underwa y to determine whether other laryngeal muscles exhibit such an unusual ly high ratio of MHC isoform polymorphism.