Unloaded Shortening Velocity and Myosin Heavy Chain Variations in Human Laryngeal Muscle Fibers

Abstract

Myosin description in human laryngeal muscles is incomplete, but evidence suggests the presence of type I, IIA, IIX, and tonic myosin heavy chain (MHC) fibers. This study describes the unloaded shortening velocity (V0) of chemically skinned laryngeal muscle fibers measured by the slack test method in relation to MHC content. Skeletal fibers from human laryngeal and limb muscle biopsy specimens were obtained for determination of V0, and subsequently, glycerol-sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to determine the MHC isoform content. The fibers from human limb muscle had shortening speeds similar to those in previous reports on human skeletal fibers. Type I, IIA, and IIX fibers of laryngeal muscle had shortening speeds similar to those of fibers from limb muscle, but laryngeal fibers with heterogeneous MHC expression had a wide range of shortening speeds, some being nearly twice as fast as limb fibers. In addition. MHC isoform bands from human extraocular muscle comigrated with some bands from laryngeal muscle -a finding suggesting that extraocular myosin may also be expressed.

Functional diversity among a family of human skeletal muscle myosin motors

“…The fact that extraocular myosin does not have light chains should not have an effect on ATPase activity based on experiments on skeletal muscle myosin (60). Several studies have shown that fibers expressing MyHC-Extraocular exhibit isometric contraction twitch times twice as fast as those from conventional skeletal muscles (29,67). The unique requirements of extraocular muscles, which contract very rapidly, repetitively, and for prolonged periods against very low load to move the eye and laryngeal muscles may indicate a specialized role for this isoform.…”

“…The ATPase activities of the developmental and the MyHC-Extraocular isoforms are less clear due to their heterogeneous expression with other isoforms. Preliminary work suggests the developmental myosins have low ATPase activities (31,32), while MyHCExtraocular is thought to be a very fast myosin (22,29,33). All of this evidence points to the conclusion that myosin isoform expression patterns are a likely mechanism for the specialization of muscles to perform specific tasks.…”

“…Myosin isotype expression has been linked to myofibrillar ATPase activity, contractile force, and unloaded contractile velocity (1, 3,4,[25][26][27][28][29][30]. This work has revealed that muscle fibers can display a wide range of biochemical and physiological properties, with their unloaded contractile velocities and ATPase activities increasing in order from Type-I, IIA, IID, to IIB.…”

Fibre architecture and song activation rates of syringeal muscles are not lateralized in the European starling

“…Laryngeal muscles in mammals are fast, but do not reach such high contraction rates as starling muscles (Martensson and Skoglund, 1964;Alipour-Haghighi et al, 1987;Alipour and Titze, 1999;Sciote et al, 2002;Hoh, 2005). Unlike toadfish sonic and rattlesnake tailshaker muscles, laryngeal muscles show heterogeneous fibre type composition (Hoh, 2005).…”

Muscle Fiber Type Composition and Effects of Vocal Fold Immobilization on the Two Compartments of the Human Posterior Cricoarytenoid: A Case Study of Four Patients

“…It is likely that some of these unusual MyHC isoforms are present in the PCA given the evidence of these isoforms in other specialized cranial muscles, and the unusual shortening velocities reported for these fibers. 4,5 Anatomical studies have shown a reliable presence of horizontal and vertical components of the posterior cricoarytenoid (PCA) muscle, but minimal information exists regarding the composition and function of these muscle subcompartments. 6 Innervation studies have demonstrated a distinct innervation pattern to different intrinsic laryngeal muscle subcompartments.…”