Effects of aging and life-long physical training on collagen in slow and fast skeletal muscle in rats

Summary Intramuscular collagen in a slow (m. soleus) and a fast (m. rectus femoris) skeletal muscle was studied by biochemical, morphometric, and immunohistochemical methods. Wistar white rats of 1, 4, 10, and 24 months were used as experimental animals. Our aim was to evaluate the effects of life-long physical training (treadmill running, 5 days a week for 1, 3, 9, and 23 months depending on the age attained). The biochemical concentration of collagen was higher in m. soleus than in m. rectus femoris and it increased in youth and in old age in m. soleus. The trained rats had higher concentrations of collagen than the untrained rats at 10 and 24 months. The morphometrically measured area-fractions of both the endomysium and perimysium were higher in m. soleus than in m. rectus femoris. The age-related increase in intramuscular connective tissue was of endomysial origin. The immunohistochemical staining of type-I, -III, and -IV collagens indicated the more collagenous nature of m. soleus as compared with m. rectus femoris for all major collagen types; this was most marked for type-IV collagen of basement membrane. The results indicate that both age and endurance-type physical training further distinguish the slow and fast muscles with respect to their connective tissue.     

Adaptive response of hypertrophied skeletal muscle to endurance training

The response of hypertrophied soleus and plantaris muscle of rats to endurance training was studied. Hypertrophy was produced by bilateral extirpation of the gastrocnemius muscle. A 13-wk training program of treadmill running initiated 30 days after removal of the gastrocnemius muscle accentuated (P less than 0.01) the hypertrophy. Succinate dehydrogenase activities of the enlarged muscles of sedentary rats were similar to those of normal animals, as were the increases associated with training. Phosphorylase and hexokinase activities were unaltered as a result of the experimental perturbations. Rates of glycogen depletion during exercise were lower (P less than 0.01) in the liver and soleus and plantaris muscles of endurance-trained animals. No difference existed in the rate of glycogen depletion of normal and hypertrophied muscle within the sedentary or trained groups. These data demonstrate that extensively hypertrophied muscle responds to training and exercise in a manner similar to that of normal muscle.     

Divalent cation binding properties of slow skeletal muscle troponin in comparison with those of cardiac and fast skeletal muscle troponins

1. New methods of preparing troponins from slow skeletal and cardiac muscle of the chicken have been developed. The electrophoretic mobilities of slow skeletal muscle troponin subunits were different from those of the corresponding fast skeletal muscle subunits. 2. A new method for determining the amount of divalent cations bound to troponin was developed. The principle of the method is to immobilize troponin by conjugating it with Sepharose 4B resin, thus making it readily sedimentable. 3. The numbers of Sr and Ca ions bound to slow muscle troponin at concentrations sufficient to produce maximum contraction were 1.73 and 1.36 mol per mol, respectively, being nearly equal to those of cardiac troponin but half of those of fast muscle troponin. 4. The concentrations of Sr and Ca ions giving half-maximal ion binding to slow muscle troponin (K50%) were 5.5 X 10(-6) M and 4.6 X 10(-7) M, respectively. 5. K50% for Sr of cardiac troponin was significantly higher than that of slow muscle troponin. Although K50% for Sr of cardiac troponin was the same as that of fast muscle troponin, cardiac troponin bound more Sr ions than fast muscle troponin at lower Sr ion concentrations. The mechanism underlying the high sensitivity of cardiac muscle contraction to Sr ions is discussed in comparison with that of slow muscle.     

Mitochondrial enzymatic adaptation of skeletal muscle to endurance training.

Some mitochondrial enzymatic activities (succinate dehydrogenase, NADH cytochrome reductase, cytochrome oxidase) were studied in the gastrocnemius and soleus muscle of the rat. The modifications of the enzyme activity, induced by endurance training, were found to be functions of 1) daily work load and 2) total training time. The treatment with an effective dose of vasodilating substances (papaverine, nicergoline, dipyridamole, and bamethan) showed that 1) nicergoline, bamethan, and dipyridamole were differently able to shorten the time of appearance of the increase in the enzymatic activities; 2) however, long-term treatments with these drugs did not prove able to modify the plateau level of the enzymatic activity increase, for a given amount of endurance training; 3) the pharmacodynamic effect on enzymatic activities was in no way related to the vasodilating effect of these drugs, since the effect was not observed with papaverine. The transition from a given level of endurance training to a lower one led to a proportional decrease of the mitochondrial enzymatic activities, thus pointing out the relation between amount of training and enzymatic activity. The drugs studied were unable to modify the decrease of enzymatic activity induced by lower work load.     

Lysosomal proteinase-sensitive regions in fast and slow skeletal muscle myosins

We investigated the limited proteolysis of fast and slow myosins purified from rabbit psoas major and semimembranosus proprius muscles, respectively, by the main lysosomal proteinases: cathepsins B, H, L, and D. In EDTA containing buffer, cathepsin D cleaved both myosins only at the rod-S1 junction leading to the formation of two S1 fragments of slightly higher Mr than the three forms obtained with chymotrypsin. On addition of MgCl2 instead of EDTA, myosin hydrolysis was markedly reduced. In contrast, irrespective of the presence of either MgCl2 or EDTA, cathepsin B hydrolysed both myosins into HMM and LMM. Cathepsin L digested myosins more extensively than cathepsins B and D and the main fragments generated were, in decreasing order of importance, rod, S1, S2, HMM, and LMM. In the incubation conditions tested, cathepsin H displayed nondetectable action on myosins. As fast and slow myosin digest patterns were compared, the main differences observed concerned the size of the proteolytic products and the rate of hydrolysis, which was about 4-fold higher for the fast than for the slow isoform. This appeared consistent whatever enzyme was considered.     

Calcium-related abnormalities in fast and slow denervated skeletal muscle in rats

Muscle weights, Ca-ATPase activity and calcium-binding proteins were studied after denervation in rat extensor digitorum longus (EDL) and soleus (Sol) muscles. Muscle weights decreased progressively as a function of denervation time: after 28 days EDL weight diminished by 70% and Sol weight by 47%. Ca-ATPase activity and calsequestrin were quite reduced in control Sol as compared to the control EDL. Denervation caused a considerable reduction in Ca-ATPase and calsequestrin in EDL, making it resemble the control Sol.     

Effect of endurance training and chronic isoproterenol treatment on skeletal muscle sensitivity to norepinephrine

The purpose of this study was to determine the influence of metabolic stresses, such as endurance training and chronic isoproterenol treatment, on skeletal muscle sensitivity to norepinephrine. Using an isolated perfused rat hindlimb preparation, dose-response curves for skeletal muscle oxygen consumption (VO2) and vascular resistance were obtained with control, endurance trained, and isoproterenol treated rats. No significant difference was found between control and experimental groups for non-stimulated VO2. In response to NE infusion, trained rats showed a significantly greater increase in VO2 compared to control rats while the response of the isoproterenol treated rats was of the same magnitude as the one for their respective control rats. At the highest dose of NE infused, the vasopressor response was significantly lower in trained rats compared to control rats. At none of the doses was there a significant difference in the vasopressor response between control and isoproterenol treated rats. These results suggest that repeated exposures to high levels of catecholamines, as produced during endurance training, leads to an increased sensitivity of skeletal muscle to the effect of norepinephrine.     

Identification of sarcolemma-associated antigens with differential distributions on fast and slow skeletal muscle fibers

We have identified three sarcolemma-associated antigens, including two antigens that are differentially distributed on skeletal muscle fibers of the fast, fast/slow, and slow types. Monoclonal antibodies were prepared using partially purified membranes of adult chicken skeletal muscles as immunogens and were used to characterize three antigens associated with the sarcolemma of muscle fibers. Immunofluorescence staining of cryosections of adult and embryonic chicken muscles showed that two of the three antigens differed in expression by fibers depending on developmental age and whether the fibers were of the fast, fast/slow, or slow type. Fiber type was assigned by determining the content of fast and slow myosin heavy chain. MSA-55 was expressed equally by fibers of all types. In contrast, MSA-slow and MSA-140 differed in their expression by muscle fibers depending on fiber type. MSA-slow was detected exclusively at the periphery of fast/slow and slow fibers, but was not detected on fast fibers. MSA-140 was detected on all fibers but fast/slow and slow fibers stained more intensely suggesting that these fiber types contain more MSA-140 than fast fibers. These sarcolemma-associated antigens were developmentally regulated in ovo and in vitro. MSA-55 and MSA-140 were detected on all primary muscle fibers by day 8 in ovo of embryonic development, whereas MSA-slow was first detected on muscle fibers just before hatching. Those antigens expressed by fast fibers (MSA-55 and MSA-140) were expressed only after myoblasts differentiated into myotubes, but were not expressed by fibroblasts in cell culture. Each antigen was also detected in one or more nonskeletal muscle cell types: MSA-55 and MSA-slow in cardiac myocytes and smooth muscle of gizzard (but not vascular structures) and MSA-140 in cardiac myocytes and smooth muscle of vascular structures. MSA-55 was identified as an Mr 55,000, nonglycosylated, detergent-soluble protein, and MSA-140 was an Mr 140,000, cell surface protein. The Mr of MSA-slow could not be determined by immunoblotting or immunoprecipitation techniques. These findings indicate that muscle fibers of different physiological function differ in the components associated with the sarcolemma. While the function of these sarcolemma-associated antigens is unknown, their regulated appearance during development in ovo and as myoblasts differentiate in culture suggests that they may be important in the formation, maturation, and function of fast, fast/slow, and slow muscle fibers.     

Changes in skeletal muscle in males and females following endurance training

Gender differences in substrate selection have been reported during endurance exercise. To date, no studies have looked at muscle enzyme adaptations following endurance exercise training in both genders. We investigated the effect of a 7-week endurance exercise training program on the activity of beta-oxidation, tricarboxylic acid cycle and electron transport chain enzymes, and fiber type distribution in males and females. Training resulted in an increase in VO2peak, for both males and females of 17% and 22%, respectively (P < 0.001). The following muscle enzyme activities increased similarly in both genders: 3-beta-hydroxyacyl CoA dehydrogenase (38%), citrate synthase (41%), succinate-cytochrome c oxidoreductase (41%), and cytochrome c oxidase (COX; 26%). The increase in COX activity was correlated (R2 = 0.52, P < 0.05) with the increase in VO2peak/fat free mass. Fiber area, size, and % area were not affected by training for either gender, however, males had larger Type II fibers (P < 0.05) and females had a greater Type I fiber % area (P < 0.05). Endurance training resulted in similar increases in skeletal muscle oxidative potential for both males and females. Training did not affect fiber type distribution or size in either gender.     

Development of ionic currents of zebrafish slow and fast skeletal muscle fibers

Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4-6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization.     

Glucose uptake after immobilization in fast and slow skeletal muscle in rats

1. 3-O-methylglucose uptake was studied after immobilization in rat extensor digitorum longus (EDL) and soleus (Sol) muscles. 2. The immobilization of the ankle was done in one of extreme positions by plaster casts. 3. In both positions, 3-O-methylglucose uptake in EDL increased and that in Sol decreased after immobilization. 4. When immobilization was released uptake returned to control level. 5. The change in uptake after immobilization and after release of immobilization was earlier in Sol.