Are hybrid fibers a common motif of canine laryngeal muscles? Single-fiberanalyses of myosin heavy-chain isoform composition

Background: The canine lateral cricoarytenoid muscle contains a large propo rtion of muscle fibers that coexpress various combinations of myosin heavy- chain isoforms tie, so-called hybrid fibers). Objective: To test the hypothesis that hybrid fibers are a common motif thr oughout laryngeal muscles. Design: The posterior cricoarytenoid, canine cricothyroid, and thyroartenoi d muscles were removed from 5 beagle dogs. The posterior cricoarytenoid and canine cricothyroid muscles were each dissected into horizontal, oblique, and rectus regions. The thyroarytenoid was separated into medial and latera l regions. Approximately 40 single fibers were microdissected from each reg ion (approximate to 1800 total fibers were sampled) and placed into a denat uring sample buffer. Sodium dodecyl sulfate-polyacrylamide gel electrophore sis was then used to separate the individual myosin heavy-chain isoforms. Results: Each laryngeal muscle contained hybrid fibers; however, the types and proportions of hybrid fibers were clearly muscle specific. Within a giv en muscle, there were relatively minor regional differences in the types an d proportions of hybrid fibers. Conclusion: If the myosin heavy-chain isoform composition of a single fiber can be used as a "physiological marker," then the extent of hybridism may reveal the diversity of activity required of a given laryngeal muscle.