Maximum shortening velocity and myosin heavy-chain isoform expression in human masseter muscle fibers.
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.
Morris
T J
TJ
The Department of Orthodontics & Dentofacial Orthopedics, University of Pittsburgh, PA 15261-1932, USA.
Brandon
C A
CA
Horton
M J
MJ
Carlson
D S
DS
Sciote
J J
JJ
D000293:Adolescent; D000328:Adult; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D016018:Least-Squares Analysis; D008297:Male; D008406:Masseter Muscle / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000737:chemistry / Q000502:physiology; D018995:Myosin Heavy Chains / Q000032:analysis / Q000502:physiology*; D024461:Myosin Type I / Q000032:analysis / Q000502:physiology*; D010641:Phenotype; D020033:Protein Isoforms / Q000096:biosynthesis / Q000502:physiology; D024744:Skeletal Muscle Myosins / Q000032:analysis / Q000502:physiology*
D020033:Protein Isoforms; D024461:Myosin Type I; D024744:Skeletal Muscle Myosins; D018995:Myosin Heavy Chains