Glycogen metabolism in white and red muscle or normal and diabetic rats. The glycogen concentration and glycogen synthesis from glucose.

The amount of glycogen and its synthesis from glucose was studied in white muscle (extensor digitorum longus -- EDL) and red muscle (soleus -- SOL) of normal rats and rats with alloxan diabetes by the anthrone method. The amount of glycogen was higher in the white muscle of normal rats, both after a 24 hours' fast (0.37+/-0.02 mg/g as against 0.29+/-0.01 mg/g in the SOL) and with feeding ad libitium (0.72+/-0.05 mg/g as against 0.58+/-0.03 mg/g in the SOL). After a 24 hours' fast, the glycogen content of both muscles was non-significantly higher in alloxan-diabetic rats than in normal animals, whereas in diabetic animals fed ad libitum it was significantly lower than in normal rats fed in the same manner (0.54+/-0.07 mg/g in the EDL and 0.33+/-0.03 mg/g in the SOL). The difference between the glycogen content of the white and red muscle of diabetic rats was also in favour of the white muscle. Muscle glycogenesis from intragastrically administered glucose was higher in the red muscle in all the experimental groups. In normal fed ad libitum the glycogen content of the EDL did not change after glucose administration, but in the SOL it rose from 0.58+/-0.03 to 0.83+/-0.05 mg/g. In fasting (24 hours) normal rats it rose sharply in both muscles, from 0.037+/-0.02 to 0.57+/-0.03 mg/g in the EDL and from 0.29+/-0.01 to 0.87+/-0.06 mg/g in the SOL. In fasting (24 hours) diabetic animals, the glycogen content rose after glucose in the SOL only, from 0.36+/-0.01 to 0.66+/-0.06 mg/g. The differences found in glycogen synthesis in the white and red muscle of normal and diabetic rats are discussed mainly from the aspect of the existence of a relationship between the glycogen concentration and glycogen synthetase activity.     

Glycogen metabolism in white and red muscle or normal and diabetic rats. Degradation of glycogen by adrenaline.

The author studied the effect of adrenaline (500 mug/kg s.c.) on the glycogen content of white (extensor digitorum longus -- EDL) and red (soleus -- SOL) muscle of normal and alloxan-diabetic rats. In normal rats, whose nutritional state varied at the time of adrenaline administration (after a 24 hours' fast, fed ad libitum or given 5 g glucose/kg as a 20% solution intragastrically 2 hours before injecting adrenaline), no marked post-adrenaline differences were found between the size of the decrease in the amount of glycogen in white and red muscle. In addition, no significant differences were found between the three groups of animals in glycogen concentration in the EDL (0.3+/-0.05, 0.35+/-0.03 and 0.26+/-0.02 mg/g) or in the SOL, apart from one exception (0.23+/-0.02, 0.2+/-0.01, and 0.51+/-0.03 mg/g), after adrenaline. The glycogen concentration in the white and red muscle of diabetic rats fed ad libitum fell to values similar to those in normal rats after adrenaline (0.32+/-0.05 mg/g in the EDL and 0.18+/-0.02 mg/g in the SOL). These results supoort the view of authors who hold that glycogenolysis is possible without pre-activation of phosphorylase; they also support the idea, expressed by Krebs, of the existence of a reciprocal relationship between phosphorylase activity and the glycogen concentration, according to which glycogen itself may influence its own degradation.     

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.     

Comparison of red and white muscle wet weight changed by age, denervation and morbid states

[Na]i, [K]i and wet weight of the extensor digitrum longus (EDL) and soleus (SOL) muscles of 9- and 52-week-old rats were measured for 7 days after sectioning of the sciatic nerve. The changes in wet weight of the EDL and SOL muscles of rats over 52 weeks and those of morbid state rats were also measured. There was no significant difference in wet weights between the EDL and SOL muscles in infant rats, but the EDL muscle became much heavier than the SOL muscle with aging. The decrease in rate of growth of wet weight of the EDL and SOL muscles caused by denervation, was greater in young rats than in mature rats. In addition, the rate of decrease was greater in the SOL muscles than in the EDL muscles in both young and mature rats. The [Na]i increased while [K]i was decreased by denervation, and the net Na+ increase and the net K+ loss were greater in young rats than in mature rats. The changing rate was more remarkable in the EDL muscles than in the SOL muscles throughout the aging process. During DOCA treatment over 4 weeks, the decrease of muscle wet weight was greater in the EDL muscles. The mechanisms which serve to maintain normal muscle wet weight in the SOL muscle after denervation or treatment with DOCA, were discussed.     

Phospholipid metabolism in red and white insect muscle

The red flight musculature of Schistocerca gregaria contains twice as much phospholipids than the white femoral musculature. In individual phospholipids the difference is greatest in phosphatidylethanolamine and phosphatidylglycerol, lowest in sphingomyeline and phosphatidylinositol. The plasmalogen content is very low. After an injection of ³²P orthophosphate the increase of specific activity during six days follows a similar course in both muscle types in phosphatidylethanolamine, sphingomyeline and phosphatidylserine but is more rapid in red than in white muscle in phosphatidylcholine (1.3 ×) and in phosphatidylinositol (5 ×). The incorporation into diphosphatidylglycerol is extremely slow. Flight induces an increase in the specific activity in phosphatidylinositol.     

Induction of action potentials in fish red muscle by denervation

The effects of denervation on the electrical membrane properties of fish red muscle were investigated. Forty to fifty hours after denervation, miniature endplate potentials disappeared abruptly and field stimulation of the nerve within the muscle failed to evoke endplate potentials, indicating that transmission failure occurred at this time. The membrane resistance of the red muscle fibre increased after denervation. Normally innervated fish red muscles do not generate action potentials in response to either nerve or direct muscle stimulation. However, approximately 3 weeks after nerve sectioning, action potentials could be induced in the muscles. The action potential was sodium-dependent, and was sensitive to tetrodotoxin. Actinomycin D injected in the early phase after operation suppressed the induction of the action potential. These results indicate that RNA synthesis is preliminary to the induction of the action potential mechanism, and that this mechanism is under neural control.     

Terminal sprouting in rat sternocostalis muscle following partial denervation

Summary The sternocostalis muscle of the rat was examined at one to five days after partial denervation and levels of terminal sprouting were assessed.The removal of one intercostal nerve caused localised degeneration which did not extend more than a few muscle fibres deep into the field of distribution of the adjacent nerve. Terminal sprouting was clearly seen at 24 h after operation and did not appear to develop further up to five days.There was no difference in the sprouting responses to section of either intercostal nerve 2, 4 or 5. There was, however, a decrease in the response with increasing distance from the cut nerve. No sprouting response was observed in the contralateral muscle.Comparison of sprouting levels of B and C type end plates revealed a greater percentage of C type end plates with sprouts. However, the response of B type end plates, considered in relation to the levels of spontaneous sprouting, was greater than that of C type end plates.     

Cell proliferation in skeletal muscle following denervation or tenotomy

Summary Autoradiographic experiments using ³H-thymidine were designed to analyse cell proliferation which occurs in skeletal muscle after denervation and after tenotomy. In mouse tibialis anterior and tongue muscles during the first 24 h after denervation or tenotomy labelling levels were low and did not differ significantly from sham operated control muscles. By 48 h after denervation and tenotomy of tibialis anterior muscles, increased levels of labelling occurred in both muscle and connective tissue nuclei. Daily pulse labelling for 7 days after denervation produced a labelling level which was 8 times that of sham operated controls, 25–30% of the total nuclear population being labelled. Denervated muscles had twice the level of labelling compared to tenotomised muscles. These results provide conclusive evidence that both denervation and tenotomy stimulate cell proliferation in skeletal muscle and it is suggested that the increased numbers of labelled muscle nuclei are likely to be the result of mitotic activity in muscle satellite cells.     

Glycolytic enzyme activity in developing red and white muscle

The activities of the constant proportion enzymes of the Embden-Meyerhof chain (triose phosphate isomerase (TIM), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGM) and enolase (ENOL)), and the activity of lactic dehydrogenase (LDH) were studied in developing red (trapezius) and white (longissimus) muscles of the pig from a fetal stage to 24 weeks postnatal. Both muscles were differentiated by two weeks postnatal in the sense that they had reached the adult level of enzyme activity. Enzyme activities were two- to three-fold greater in the longissimus than in the trapezius. Enzyme activity ratios based on GAPDH were not consistent in the fetal and day 1 samples but were consistent during later stages of growth. Ratios of enzyme activity based on activity at 105 days gestation revealed that TIM, PGK and PGM are grouped and follow the same pattern, but GAPDH and ENOL are quite different from each other and from the pattern shown by TIM, PGK and PGM. The constant proportion concept in developing muscle is therefore questioned.     

Proteomic analysis of rat laryngeal muscle following denervation

Laryngeal muscle atrophy induced by nerve injury is a major factor contributing to the disabling symptoms associated with laryngeal paralysis. Alterations of global proteins in rat laryngeal muscle following denervation were, therefore, studied using proteomic techniques. Twenty-eight adult Sprague-Dawley rats were divided into normal control and denervated groups. The thyroarytenoid (TA) muscle was excised 60 days after right recurrent laryngeal nerve was resected. Protein separation and identification were preformed using 2-DE and MALDI-MS with database search. Forty-four proteins were found to have significant alteration in expression level after denervation. The majority of these proteins (57%), most of them associated with energy metabolism, cellular proliferation and differentiation, signal transduction and stress reaction, were decreased levels of expression in denervated TA muscle. The remaining 43% of the proteins, most of them involved with protein degradation, immunoreactivity, injury repair, contraction, and microtubular formation, were found to have increased levels of expression. The protein modification sites by phosphorylation were detected in 22% of the identified proteins that presented multiple-spot patterns on 2-D gel. Significant changes in protein expression in denervated laryngeal muscle may provide potential therapeutic strategies for the treatment of laryngeal paralysis.