ABSTRACT
We examined the time course of soleus muscle fiber type composition. Soma area and succinate dehydrogenase (SDH) activity of soleus motoneurons during three weeks of hindlimb suspension (HS) in rats. Adult female Wistar rats (n=34, 252-288g BW) were divided into four groups: control (n=8), hindlimb suspended for one week (HS 1 wk, n=8), two weeks (HS 2 wk, n=9), and three weeks (HS 3 wk, n=9) . Soleus muscle fiber composition was calculated from transverse sections stained for myosin ATPase (preincubation pH 10.3, 4.3) . The fiber type composition did not change in the HS 1 wk, but in the HS 2 wk and HS 3 wk, the proportion of type I fibers decreased and that of type IIc and ha fibers increased. Using a fluorescent neuronal tracer nuclear yellow, motoneurons innervating the soleus muscle were identified, and the soma area and SDH activity were measured. The soma area did not change for up to two weeks of HS, but decreased in the HS 3 wk. Compared with control, SDH activity of soleus motoneurons decreased in the HS 1 wk. However, in the HS 2 wk, the activity increased to the level of control. In the HS 3 wk, the activity tended to increase further. Generally, muscle fibers and their motoneurons have unitary characteristics. However, these results suggest that change in soleus muscle fiber composition are not accompanied by changes in soma area and SDH activity in soleus motoneurons during three weeks of HS.
ABSTRACT
The present study was designed to determine whether conversion of fiber types (type I to II) induced by hindlimb unloading (HU) is identical along the length of fibers in the soleus (SOL) muscle. After 1 and 2 wk HU, SOL was divided into three (proximal, middle and distal) regions and the fiber type composition was determined using myosin adenosinetriphosphatase (ATPase) . There was no significant change in fiber type distribution after 1 wk of HU. The percentage of type I fibers significantly decreased in the proximal and middle regions and that of type IIc fibers increased in all regions after 2 wk of HU. The percentage of type IIc fibers greatly increased in the proximal and middle regions compared with the distal region. Serial cross-sections every 300μm were processed for myosin ATPase from the middle to the distal region, and then analyzed to show the differences in staining characteristics along the length of single fibers. After 2 wk of HU, some of the fibers (3.1±1.2%) displayed changes in the staining characteristics of myosin ATPase (pH 10.3) ; 84% of these fibers identified type IIc fibers in the middle region were observed as type I fibers in the distal region. These results suggest that muscle fibers in unloaded SOL may not transform synchronously or uniformly along their length
ABSTRACT
Myosin light chain patterns were examined in single fibers from the extensor digitorum longus (EDL) and soleus muscles of Wistar strain rats. The fiber type composition of both muscles was also determined to estimate the relationship between myosin light chain patterns and histochemical fiber types.<BR>The results were summarized as follows ;<BR>1. All of single fibers from the EDL muscle was typical fast type which contained fast light chains only (fLC 1·fLC 2·fLC 3), except that there was one mixed type fiber cotaining both fast and slow light chains (fLC 1·fLC 2·sLC 1·sLC 2) .<BR>2. There were two myosin light chain patterns in single fibers from the soleus muscle. One was typical slow type which contained slow light chains only (sLC1·sLC 2) and the other, mixed type in which fast and slow light chains coexisted. Mixed type fibers were divided into eight groups based on the light chain composition. The percentage occurence of typical slow type and mixed type fibers was 35.4% and 64.6%, respectively.<BR>3. The average percentage of type II fibers was 94.6% in the EDL muscle 5.4% in the soleus muscle.<BR>4. These results suggest that both fast and slow skeletal muscles contain mixed type fibers. The results further imply that in slow skeletal muscle, myosin light chain pattern of mixed type occurs not only in type II but also in type I fibers.
ABSTRACT
The inter of this study was to observe the effects of training on histochemical and biochemical properties in the skeletal muscle fibers.<BR>Wistar strain albino rats were assigned to endurance (E), sprint (S) and control (C) group at 4 weeks old. Animals of trained groups were trained by treadmill for 12 weeks. After training, all animals were sacrificed and M. Soleus (SOL) and M. Extensor Digitorum Longus (EDL) were taken out.<BR>Using histochemical staining methods for Hematoxylin and Eosin, Actomyosin ATPase and Succinate Dehydrogenase (SDH), area and composition of the three muscle fiber types were examined. Furthermore, the chemical properties of glycolytic and oxidative enzyme activities were examined.<BR>The results obtained were as follows:<BR>1. The E and S trained groups, respectivelly, showed lower increase of body weight than the control group.<BR>2. Hypertrophy of all fiber types in EDL were observed in the both trained groups. Area of SO fibers in SOL were also increased in the E group as compared to the C group.<BR>3. The differences observed for fiber composition among the three groups. The rate of FOG fiber in SOL decreased significantly in the both trained groups as compared to the C group. The rate of SO fiber in both muscles were slightly higer for the E group relative to the C Group, but these differences were no significant. However, in the E group significant increase was observed for oxidative enzyme activity. The Phosphofructo-kinase activity in EDL of the S group was significantly higher in comparison to the other groups.<BR>These results suggested that there is the discrepancy between histochemical proper-ties and biochemical properties in the effects of training on skeletal muscle fibers and that the necessity of histochemical and biochemical analysis.