Cytochrome c protein synthesis rate in rat skeletal muscle.

Endurance training is associated with increases in mitochondrial density, of which cytochrome c protein is an index. Increases in the synthesis rates of cytochrome c protein in skeletal muscle during endurance training have been inferred (Biochem. Biophys. Res. Commun. 66: 173, 1975; J. Biol. Chem. 252: 416, 1977). One purpose of the present study was to test these indirect approximations with direct measurements of the synthesis rates of cytochrome c protein in skeletal muscles postexercise. No change in the fractional synthesis rate of cytochrome c was detected in the red quadriceps muscle of rats either 2-7 h after a 104-min run on a motor-driven treadmill or 17-22 h after the final bout of 4 days of running 100 min/day. If the 16% increase in cytochrome c protein concentration in the red quadriceps muscle on the 5th day of training is used to calculate the nanomoles of cytochrome c synthesized per gram of wet muscle weight, the normalized rate of cytochrome c protein synthesis is increased 29% on the 5th day of training. The observation of no significant alteration in cytochrome c mRNA in the red quadriceps muscle of rats during the 1st wk of training implies that the initial increase in the synthesis rate of cytochrome c protein normalized per unit of muscle mass during treadmill training is likely to occur at a translational or posttranslational step. These results suggest that the control of increased cytochrome c expression in skeletal muscle during exercise training involves a complex mechanism.     

Effect of denervation on pigeon slow skeletal muscle

Summary The slow anterior latissimus dorsi muscle (ALD) of the pigeon was denervated surgically and examined after varying post-operative intervals. Muscles were studied with respect to changes in weight, histological and ultrastructural alterations, and changes in size and number of fibers. The weights of the denervated muscles increased over the contralateral control, reaching a maximum hypertrophy in the first 18 days, but the hypertrophy persisted for several months. The fibers of the denervated muscle did not hypertrophy. They showed a gradation in size from the posterior to the anterior border, with the fibers in the anterior third of the muscle being the smallest. After measuring cross-sectional sizes from the anterior, middle, and posterior thirds of the muscle, the overall fiber change was one of atrophy.Morphologically, the fibers showed various signs of pathological changes, including nuclear proliferation, swelling and migration away from the sarcolemmal position, vacuolation, myofibril degeneration, connective-tissue infiltration and replacement of the fibers, and regenerative activities in the form of budding and myoblast formation. A condition termed a peripheral rim of degeneration is described. Although many abnormal conditions were found in these denervated muscles, much of the muscle appeared normal; the neurotrophic relationship of slow muscle is discussed.This investigation was supported in part by a Public Health Service Fellowship, 2 F 2 NB 35, 582, from the National Institute of Neurological Diseases and Stroke, and by an Ohio University Research Grant to R. Hikida; and a grant 5 RO 1 AN 10856 from the National Institute of Arthritis and Metabolic Diseases to W. Bock.The authors wish to acknowledge gratefully the skillful technical assistance of Mr. Lawrence Mezza and Miss Sally Mitchell.     

Effect of denervation and phentolamine on the thermogenic action of noradrenaline in rat skeletal muscle

Vascularly isolated skeletal muscle of the cold-acclimated (CA) rat was perfused with blood in situ or in vitro and the effect of denervation and an alpha-adrenolytic agent (phentolamine) on its oxygen consumption was studied in the resting state and after administering noradrenaline (NA). The resting metabolism of muscle in situ rose by 28% after denervation. The infusion of NA further raised the oxygen consumption of acutely denervated muscle perfused in situ of in vitro by 43%. The thermogenic effect of NA on muscle denervated two hours before the experiment was only transitory. Phentolamine raised the oxygen consumption of the innervated muscle in situ by 42%; the infusion of NA did not stimulate metabolism any further. Phentolamine reduced the vascular resistance of resting muscle, but did not inhibit the vasoconstriction during the infusion of NA. The results show that the thermogenic effect of infused NA in perfused muscle is inhibited not by acute denervation, but by a vasoconstriction, which cannot be prevented by the administration of an alpha-adrenolytic agent.     

Characteristics of contractile properties of the cat skeletal muscle after sympathetic denervation]

Twitching and tetanus were registered during stimulation in the cat desympathised m. semitendinosus, similar to those occurring in the motor units during thermoregulatory tone. The contractile responses were greater in the early desynpathisation phase. By the 14th day, the contractile responses became similar to those of the control.     

Effect of reinnervation on collagen synthesis in rat skeletal muscle.

The effect of reinnervation on the activities of prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyltransferase (GGT), both enzymes of collagen biosynthesis, and on the concentration of hydroxyproline (Hyp) was studied in gastrocnemius, soleus, and tibialis anterior muscles of rat 19, 26, 40, and 61 days after crush denervation of the sciatic nerve. The GGT activity was elevated in denervated gastrocnemius and soleus muscles and the PH activity in gastrocnemius. Muscular Hyp concentration was increased in denervated tibialis anterior muscle. Both the PH and GGT activities and the Hyp concentration returned to the control level during the reinnervation period (19-61 days from the start of denervation). It seems that denervation atrophy of skeletal muscle is associated with an increased rate of muscular collagen biosynthesis and that during reinnervation collagen synthesis rate decreases despite accelerated muscular growth. The results thus suggest that innervation is a powerful suppressive regulator of muscular collagen biosynthesis.     

Effect of denervation on loss of ions in chick skeletal muscle

Leaching behaviour of chick gastrocnemius muscle has been studied with respect to the loss of Na+, K+ and Ca2+ ions in a donor-solvent (muscle-water) system under normal as well as denervated conditions. An attempt has been made to explain the alterations in the rate of electrolytic loss in terms of membrane dysfunctions induced as a result of loss of neural control.     

Influence of denervation and reinnervation on autolytic activity and on protein composition of skeletal muscle in rat.

Changes in the proteolytic activity and in the relative content of protein in soluble, myofibrillar and insoluble fractions were investigated following denervation and reinnervation of the soleus and tibialis anterior muscles of the rat. After denervation an increase of autolysis in the acid and neutral pH range, but not in the alkaline one, was found in both muscles. An increased autolysis at the acid and neutral pH range was also observed in both muscles after reinnervation, when the weight of the muscles increased. The results indicate the lack of inverse relationship between the changes of proteolytic activity and the decrease or increase of the amount of muscle protein in the course of muscle atrophy and regeneration.     

Effect of denervation on the synthesis of ribonucleic acid and deoxyribonucleic acid in rat diaphragm muscle

1. The effect of unilateral denervation of rat diaphragm muscle on its content of nucleic acids and their incorporation of precursors was investigated. 2. After denervation the paralysed hemidiaphragm hypertrophies and within 3 days its content of RNA increases considerably. The concentration of DNA/unit mass remains fairly constant. 3. During this period there is some increase in the rate of incorporation of [(14)C]adenine into RNA, whereas there is some diminution in the rate of incorporation of [(14)C]orotic acid. 4. Incorporation of [(14)C]adenine and [(3)H]thymidine into DNA is much increased in the paralysed tissue, reaching its maximum by about the third day, but returning to normal by the tenth. 5. The significance of these results in relation to the hypertrophy after denervation is discussed.     

Effect of denervation or unweighting on GLUT-4 protein in rat soleus muscle.

The purpose of this study was to test the hypothesis that the decreased capacity for glucose transport in the denervated rat soleus and the increased capacity for glucose transport in the unweighted rat soleus are related to changes in the expression of the regulatable glucose transporter protein in skeletal muscle (GLUT-4). One day after sciatic nerve sectioning, when decreases in the stimulation of soleus 2-deoxyglucose (2-DG) uptake by insulin (-51%, P less than 0.001), contractions (-29%, P less than 0.05), or insulin and contractions in combination (-40%, P less than 0.001) were observed, there was a slight (-18%, NS) decrease in GLUT-4 protein. By day 3 of denervation, stimulation of 2-DG uptake by insulin (-74%, P less than 0.001), contractions (-31%, P less than 0.001), or the two stimuli in combination (-59%, P less than 0.001), as well as GLUT-4 protein (-52%, P less than 0.001), was further reduced. Soleus muscle from hindlimb-suspended rats, which develops an enhanced capacity for insulin-stimulated glucose transport, showed muscle atrophy similar to denervated soleus but, in contrast, displayed substantial increases in GLUT-4 protein after 3 (+35%, P less than 0.05) and 7 days (+107%, P less than 0.001). These results indicate that altered GLUT-4 expression may be a major contributor to the changes in insulin-stimulated glucose transport that are observed with denervation and unweighting. We conclude that muscle activity is an important factor in the regulation of GLUT-4 expression in skeletal muscle.     

Lysosomes in skeletal muscle following denervation

Summary The in-vivo uptake of exogenously applied horseradish peroxidase and the activities of the lysosomal enzymes acid phosphatase and cathepsin D were studied histochemically and/or biochemically in innervated and 2–14 day-denervated tibialis anterior muscles of the mouse. The biochemically determined uptake of horseradish peroxidase showed a large increase already 4 days after denervation. The activities of the lysosomal enzymes increased in a more gradual fashion, and only cathepsin D showed an increase in activity when expressed as total activity per muscle. Histochemically horseradish peroxidase was found to be localized in muscle fibres in characteristic spindle-shaped segments after denervation. The main increase in the number of such segments per transverse section of the muscle occurred between 3 and 6 days after denervation. In serial sections these segments frequently showed positive staining also for acid phosphatase.It is concluded that exogenously applied horseradish peroxidase is taken up into the lysosomal system, which after denervation becomes organized into characteristic spindle-shaped segments in the muscle fibres. The endocytic activity of muscle fibres increases early after denervation. This is followed by a more gradual increase in activity of lysosomal enzymes and finally by an organization of the lysosomal system into characteristic spindle-shaped segments. The results are compatible with the working hypothesis that increased endocytosis may initiate lysosomal activation in denervated skeletal muscle.     

Effect of denervation on the expression of glycogen phosphorylase in mouse skeletal muscle.

After sciatectomy of the left hind-limb of C57BL/J mice, a denervation-induced muscular atrophy ensued and was accompanied by a decrease in the specific activity of glycogen phosphorylase to approx. 25% of control values. The cofactor of phosphorylase, pyridoxal 5'-phosphate, was used as a specific label in the determination of the degradation rate of the enzyme following nerve section. After a delay of 3-4 days, phosphorylase was degraded approx, twice as rapidly in the denervated gastrocnemius (0.20 day-1) as in the control muscle (0.12 day-1). The effect of denervation on phosphorylase mRNA was measured by quantitative Northern-blot analysis using a rat skeletal-muscle phosphorylase cDNA probe. After an initial rapid decline, phosphorylase mRNA levels stabilized in denervated muscle at 50% of the value measured in the contralateral control muscle.     

Effects of denervation and colchicine treatment on the chloride conductance of rat skeletal muscle fibers

Membrane potentials, cable parameters, and component resting conductances were measured in extensor digitorum longus (EDL) muscle fibers from adult rats in vitro at 24°C, after 15 to 18 days of denervation by nerve section, and at seven to ten days following epineural injection of 100 to 450 μg of colchicine in the peroneal nerve. The denervated muscles were paralyzed throughout the experimental period, whereas the colchicine-treated preparations showed no clinical paralysis except for the first day or two. The EDL from the untreated side served as a control. Both the denervated and colchicine-treated fibers were depolarized, showed signs of fibrillation, had tetrodotoxin-resistant action potentials, and membrane resistance was increased two- to sevenfold. In the denervated fibers, mean chloride conductance G_Cl dropped from a control value of 3196 to 596 μmhos/cm² while mean potassium conductance G_K showed a tendency to rise from 260 to 332 μmhos/cm². Colchicine-treated fibers while showing a similar fall in mean G_Cl from 2993 to 1066 μmhos/cm², also showed a significant fall in mean G_K from 213 to 116 μmhos/cm². It was concluded that factors transported by the microtubular system are important for the maintenance of the high resting G_Cl of mammalian skeletal muscle fibers.