Distribution of Myosin Heavy Chain Isoform in Human Extraocular Muscles

PURPOSE: To provide quantitative data on the distribution of MyHCeom and compare the proportion of myosin heavy chain (MyHC) isoforms between the central and peripheral regions of human extraocular muscles (EOMs). METHODS: Medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscle samples were taken from three men with brain death. To examine the longitudinal distribution of myosin isoforms, the muscles were divided into central and peripheral portions of equal length. Electrophoresis and densitometry were used to quantify the distribution of MyHC isoforms. RESULTS: Electrophoresis of whole-muscle extracts of sampled EOMs revealed four MyHC bands that were identified as MyHCI, MyHCeom, MyHCIIa, and MyHCIIx. The proportion of MyHCeom was higher in the central region, whereas the proportion of MyHCIIa was higher in the peripheral region. The relative proportions of MyHCI, MyHCeom, and MyHCIIa were not significantly different among the EOMs. There was a tendency for higher levels of MyHCIIx in the inferior rectus muscle. CONCLUSIONS: The proportion of MyHCeom was higher in the central region of human EOMs. Further studies are needed to investigate the consequences of this distributional difference on the function of EOMs.

The Effect of Sprint and Heavy Resistance Training on Muscle Strength, Endurance and Muscle Fiber Type

OBJECTIVE: The purpose of this study is to compare muscle strength, endurance and the change of myosin heavy chain isoform after sprint training(ST) and heavy resistance training(HRT). METHOD: Fourteen young athletes were enrolled and were randomly assigned into each training group. Before and after training for 8 weeks, the strength and the endurance were evaluated using isokinetic exercise system(Cybex 6000). The specimens of muscle biopsy were obtained from vastus lateralis muscle and were analysed for muscle fiber type using one dimensional electrophoresis. RESULTS: Peak torque, total work and mean power were increased significantly in both groups, but endurance ratio increased only in the sprint training group(P0.05). CONCLUSION: This study shows that it is possible to increase muscle strength and to achieve fiber type transformation with the sprint training and the high resistance training.

Changes in contractile properties, fiber type and myosin heavy chain isoform compositions of rat skeletal muscle induced by chronic overload / 体力科学

The effects of chronic overload by synergist ablation (SA) on fiber type, myosin heavy chain (MyoHC) isoforms, and contractile properties in the rat plantaris muscle were studied. Plantaris muscle was overloaded by bilateral removal of its synergist of gastrocnemius muscle in Fischer 344 female rats (aged 8 weeks) . Muscles of sham-operated legs served as controls.<BR>The overloaded plantaris was 20% heavier than control 3 weeks after SA. Overload by SA resulted in remarkable increases in cross-sectional areas of muscle fibers of all types ; however, the percentage increase was less in type II b fibers. Twitch contraction and half-relaxation time before and after tetanus did not change, but fatigue resistance increased significantly with overload. The percentage of area occupied by type II b fibers, which have lower oxidative capacity, decreased while the percentage of area occupied by other type II fibers, but not type I fibers, increased. Analysis of MyoHC isoforms with gradient sodium dodecylsulfate polyacrylamide gel electrophoresis revealed a decrease in II b isoforms and an increase in II d isoforms.<BR>These results suggest that chronic overload produces changes in muscle fiber type and MyoHC isoform compositions which partly account for increased fatigue resistance in overloaded muscles.

Changes in myosin heavy chain isoform composition of rat skeletal muscles as a result of running and jumping trainings / 体力科学

Four myosin heavy chain (MHC) isoforms were detected in rat hind-limb fast muscles. MHC isoforms are particularly good candidates for fiber type-specific markers in myofibril proteins. We studied the effect of running or jumping training on MHC isoform composition in 18, 6 month-old female rats. The animals were divided into three groups : sedentary (S; n=6), running (R; n=5) and jumping (J; n=7) at 4 months of age. Animals in group R were trained with treadmill running (30 m/min, 60 min/day and 5 days/wk) for 8 weeks. Animals in group J were trained with vertical jumping (40 cm high, 100 repetitions/day, 5 days/wk) for 8 weeks.<BR>There was no significant difference in body weight among the groups. Muscle weight and muscle weight/body weight for the plantaris were significantly increased in both trained groups, but there was no significant difference in the protein concentration. With regard to MHC isoform composition, there was no significant difference in the compositions of the type I and type ha MHC isoforms. In the type lid MHC isoform, the values for both trained groups were significantly higher than that of group S (p<0.05) . The values for both trained groups in the type lib MHC isoform were lower than that of group S. In particular, there was a significant difference between groups S and J (p<0.05) .<BR>These results indicate that a relative increment of the type lid MHC isoform is a typical adaptation phenomenon of the olantaris muscle in rats riven runninr and iumoinr training.