Abstract
This study examines the myosin isozyme heterogeneity (in terms of both alkali light chains and myosin heavy chains) among skeletal muscle fibers of the rabbit and correlates these isozyme differences with the differences in a contractile property, the velocity of unloaded shortening, of the fibers. The mean velocities of unloaded shortening (pCa 4.3; 12 degrees C) were as follows: psoas IIb fibers, 2.07 fiber lengths/s (n = 25); tibialis anterior (IIb) fibers, 1.63 fiber lengths/s (n = 18); vastus intermedius IIa fibers, 0.98 fiber lengths/s (n = 15); fibers (IIa) from chronically stimulated tibialis anterior, 0.86 fiber lengths/s (n = 16). Peptide maps of the myosins showed that the myosin heavy chains of the two groups of IIb fibers were indistinguishable from each other, but different from the heavy chains of the IIa fibers. However, the difference in maximal shortening velocity of the two groups of IIb fibers was correlated with a difference in the alkali light chain ratio deduced from the intensity ratio of myosin isoforms separated by gel electrophoresis under nondenaturing conditions. The vastus intermedius (IIa) and chronically stimulated tibialis anterior (IIa) fibers were indistinguishable in terms of either velocities of unloaded shortening or myosin isozyme contents. Soleus fibers contained only slow-twitch myosin. Thus, among fibers that contained a variety of myosin isozymes, differences in shortening velocities were correlated with the alkali light chain ratio, myosin heavy chain type, or a combination of both.
Highlights
From the Slnstitute for Neurological SciencesResearch and Department of Kineswlogy, University of Texas at Austin, Austin, Texas 78712; TDepartment of Radiology, Harvard Medical Schooland Department of Radiology, Brigham and Women’s
18);vastus intermedius IIafibers, 0.08 fiber lengths/s (n= 16); fibers (IIa) from chronically stimulatedtibiof myosin of rabbit skeletal muscle fibers of histochemically defined types, Seven sarcomeric myosin heavy chain genes have been found in rat; with the exception of the a-heavy chain gene of cardiac muscle, all have been found to be expressed in skeletal muscle (Mahdavi et d..,1986)
Some fibers contain shorteningvelocity of thetwo groups ofIIb fibers was either mixtures of IIa and Iheavy chains or IIa and IIhbeavy correlated with a difference in the alkali light chain chains (Staron and Pette,1987a, 1987b), givingrise to interratio deduced from the intensity ratio of myosin iso- mediate fiber types (Staron forms separated by gel electrophoresis under nonde- and Pette, 1986,1987a, 1987b)
Summary
18);vastus intermedius IIafibers, 0.08 fiber lengths/s (n= 16); fibers (IIa) from chronically stimulatedtibiof myosin of rabbit skeletal muscle fibers of histochemically defined types, Seven sarcomeric myosin heavy chain genes have been found in rat; with the exception of the a-heavy chain gene of cardiac muscle, all have been found to be expressed in skeletal muscle (Mahdavi et d..,1986). In adult limb muscles only alis anterior, 0.86 fiber lengths/s(n= 10); soleus type three of the myosin heavy chain genes are expressed; the type. The majority of rabbit limb the two groupsofIIb fibers were indistinguishable muscle fibers surveyedby ourselves (Mabuchi et al.,1984)and from each other, butdifferent from the heavy chains others (Staron and Pette, 1986,1987a, 1987b) contain only of the IIa fibers.
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