Journal of Dental Research, Vol 80, 1845-1848, Copyright © 2001 by International & American Associations for Dental Research Online Journals

ARTICLES

Maximum shortening velocity and myosin heavy-chain isoform expression in human masseter muscle fibers

J. Morris T, A. Brandon C, J. Horton M, S. Carlson D and J. Sciote J
The Department of Orthodontics & Dentofacial Orthopedics, University of Pittsburgh, PA 15261-1932, USA.

While human masseter muscle is known to have unusual co-expression of myosin heavy-chain proteins, cellular kinetics of individual fibers has not yet been tested. Here we examine if myosin heavy-chain protein content is closely correlated to fiber-shortening speed, as previously reported in other human muscles, or if these proteins do not correlate well to shortening speeds, as has been demonstrated previously in rat muscle. Slack-test recordings of single, skinned human masseter fibers at 15 degrees C revealed maximum shortening velocities generally slower and much more variable than those recorded in human limb muscle. The slowest fiber recorded had a maximum shortening velocity (V0) value of 0.027 muscle lengths x s(-1), several times slower than the slowest type I fibers previously measured in humans. By contrast, human limb muscle controls produced V0 measurements comparable with previously published results. Analysis by gel electrophoresis found 63% of masseter fibers to contain pure type I MyHC and the remainder to co-express mostly type I in various combinations with IIA and IIX isoforms. V0 in masseter fibers forms a continuum in which no clear relationship to MyHC isoform content is apparent.

This article has been cited by other articles:

				J.A.M Korfage, J.H. Koolstra, G.E.J. Langenbach, and T.M.G.J. van Eijden Fiber-type Composition of the Human Jaw Muscles--(Part 2) Role of Hybrid Fibers and Factors Responsible for Inter-individual Variation J. Dent. Res., September 1, 2005; 84(9): 784 - 793. [Abstract] [Full Text] [PDF]

				J.A.M. Korfage and T.M.G.J. Van Eijden Myosin Heavy-chain Isoform Composition of Human Single Jaw-muscle Fibers J. Dent. Res., June 1, 2003; 82(6): 481 - 485. [Abstract] [Full Text] [PDF]