Effect of denervation on the levels and rates of synthesis of specific enzymes in “fast-twitch” (breast) muscle fibers of the chicken

Abnormal fatty acid metabolism in spinal muscular atrophy may predispose to perioperative risks

A 15 year old boy with SMA type II underwent spinal fusion and suffered a mitochondrial Reye-like catabolic crisis 4 days postop with hypoketotic hypoglycemia, lactic acidaemia, hyperammonemia and liver failure, with 90% coagulative necrosis and diffuse macro- and microvesicular steatosis, requiring orthotopic liver transplantation. This crisis responded in part to mitochondrial therapy and anabolic rescue. He made a dramatic sustained neurological recovery, though his post-transplant liver biopsies revealed micro- and macrosteatosis. We hypothesize that a combination of surgical stress-catecholamine induced lipolysis, prolonged general anaesthesia with propofol and sevoflurane, and perioperative fasting on a background of decreased β-oxidation were potential risk factors for the mitochondrial decompensation.

Regulatory expression of MDP77 protein in the skeletal and cardiac muscles

The mdp77 gene was first cloned from the cDNA library of denervated chick muscles, while its role(s) in vivo was unknown. In the present study, using specific polyclonal antibodies against MDP77, we show that MDP77 was expressed specifically in the skeletal and cardiac muscle, and confirm its presence in the cytoplasm of the extrafusal muscle fibers. In mature muscles, MDP77 immunoreactivity was observed in a repetitive manner along the sarcomere. The onset of MDP77 expression occurred just after myotube formation both in vivo and in vitro. Furthermore, MDP77 was enriched in the intrafusal muscle fibers. Our findings suggest that MDP77 plays an important role(s) in the differentiation, maturation and function of both the skeletal and cardiac muscles.

Reduced glycogen phosphorylase activity in denervated hindlimb muscles of rat is related to muscle atrophy and fibre type

Changes in the activity of muscle glycogen synthase or phosphorylase (GP) may be responsible for the deregulation of glycogen synthesis and storage which occurs in diabetes mellitus. To clarify the relationship between muscle atrophy, fibre type, insulin-stimulated glucose uptake and GP activity during insulin resistance, we used sciatic nerve severance to induce insulin resistance in rat hindlimb muscles and compared the above parameters in muscles with a range of fibre types. Changes were analysed by comparison with the contralateral hindlimb, which bears more weight due to denervation of the opposing limb, as well as the sham-operated and contralateral limb of a separate rat. Denervation caused a decrease in insulin-stimulated glucose uptake by 1 day after denervation and a decline of GP activity after 7 days in all muscles investigated. GP activity decreased by 73% in soleus, 36% in red gastrocnemius, 35% in tibialis and 13% in white gastrocnemius, which was related to the degree of muscle atrophy and inversely related to the overall GP activity in non-denervated muscles. GP activity in muscles of the contralateral limb from the denervated rat did not differ from either hindlimb of the sham-operated rat. We conclude that the fibre-type related reduction in insulin-stimulated glucose uptake of denervated muscle determines the change in its metabolism and it is this metabolic change which determines the mechanism, rate and degree of muscle atrophy, which is directly related to the decline in GP activity.

Proximal sequences of the aldolase A fast muscle-specific promoter direct nerve- and activity-dependent expression in transgenic mice

Muscle activity is known to modulate the muscle fiber phenotype. Changes in muscle activity (normal or experimentally induced) lead to modifications of the expression status of several muscle-specific genes. However, the transcription regulatory elements involved in the adaptative response are mainly unknown. The aldolase A muscle-specific promoter, pM, is expressed in adult fast twitch muscle with a preferential expression in fast glycolytic-2B fibers. Its activity is induced during postnatal muscle maturation, suggesting a role of nerve and/or muscle activity. Indeed, denervation of gastrocnemius in newborn mice prevented the activation of the promoter in this muscle, despite the nerve-independent formation of 2B fibers. Although the nerve was necessary for pM onset during development, denervating the gastrocnemius in adults had only mild effects on pM activity. By contrast, a transgene including the pM proximal regulatory sequences that are sufficient to reproduce the 2B fiber-specific expression of the endogenous promoter was shown to be highly sensitive to both neonatal and adult denervation. Transgenes containing muscle-specific pM proximal promoter elements were used to delineate the regulatory elements involved in this response to innervation and changes in the contractile activity pattern. Nerve- and activity-dependent elements could be localized in the 130-base pair-long proximal promoter region of the human aldolase A gene.

Sarco(endo)plasmic reticulum Ca2+ pump and metabolic enzyme expression in rabbit fast-type and slow-type denervated skeletal muscles. A time course study

Recent reports by d'Albis et al. have shown that denervation of 8-day-old rabbit fast-twitch muscle (gastrocnemius) leads to the transformation of the muscle towards a slow phenotype but the changes towards slow-type myosin isoforms and contractile properties of the muscle were temporally uncoordinated. We analyzed the time course of the effects of denervation of the gastrocnemius on the expression of the sarcoplasmic reticulum calcium pump isoforms (SERCA) and on the metabolic state of the muscle. Northern-blot analysis showed a rapid loss of the fast Ca2+ pump isoform (SERCA 1) mRNA from the denervated gastrocnemius which became of the oxidative type. The changes observed were complete as early as 35 days post-natal, i.e at the time when changes in contractile properties were previously observed. Denervation of the slow-twitch soleus led to a 50% decrease in the level of the slow Ca2+ pump isoform (SERCA 2) mRNA and was without effect on the metabolic state of the muscle. These findings extend previous results suggesting that in rabbit, continuous innervation is required for differentiation of fast-twitch muscles but is not an absolute requirement for differentiation of the slow-twitch muscle.

Regulation of the myoblast-specific expression of the human beta-enolase gene

The muscle-specific beta-enolase gene is expressed in proliferating adult myoblasts as well as in differentiated myotubes. Through deletion-transfection analysis, we identified a 79-base pair enhancer from the beta-enolase gene that leads to high level expression of a reporter gene in myoblasts, but not in fibroblasts. Following myoblast differentiation into myotubes, the activity of the enhancer declined, indicating that beta-enolase gene expression in myotubes is mediated by other regulators, possibly the myogenic helix-loop-helix family of transcription factors. Electrophoretic mobility shift assays indicated that proteins present in myoblast nuclear extracts specifically bind to the 3' half of the 79-base pair enhancer. This region contains an ets DNA-binding motif which is required not only for high level activity in myoblasts, but also for repressing activity in fibroblasts. Furthermore, the beta-enolase myoblast-specific enhancer shows limited similarity to the myoblast-specific enhancer associated with the human desmin gene, suggesting that gene expression in adult myoblasts may be coordinately regulated.

Fatty acid oxidation abnormalities in childhood-onset spinal muscular atrophy: primary or secondary defect(s)?

The purpose of this study was to further identify and quantify the fatty acid oxidation abnormalities in spinal muscular atrophy, correlate these with disease severity, and identify specific underlying defect(s). Fifteen children with spinal muscular atrophy (3 type I, 8 type II, 4 type III) were studied. Serum carnitine total/free ratios demonstrated a tendency toward an increased esterified fraction ranging 35-58% of total carnitine (normal: 25-30% of total) in younger children with types I and II. The remaining type II and III patients, older than 23 months of age at sampling, had normal esterified carnitine levels. Urinary organic acid analysis demonstrated mild to moderate medium-chain dicarboxylic aciduria in type I patients and normal, mild, or moderate increases in short-chain and medium-chain organic acids in type II patients. In the type III group, the organic acids were normal except for one patient with mild medium-chain dicarboxylic aciduria. Muscle intramitochondrial beta-oxidation was measured in 5 children (2 type I, 2 type II, and 1 type III) and a significant reduction in the activities of short-chain L-3-hydroxyacyl-CoA dehydrogenase, long-chain L-3-hydroxyacyl-CoA dehydrogenase, acetoacetyl-CoA thiolase, and 3-ketoacyl-CoA thiolase were found; however, normal crotonase activity was documented. Most strikingly, there was a marked increase (3- to 5-fold) in the activity ratios of crotonase to L-3-hydroxyacyl-CoA dehydrogenase and thiolase activities with both short- and long-chain substrates. The combined abnormalities suggest a defect in a mitochondrial multifunctional enzyme complex, distinct from the trifunctional enzyme. These abnormalities may be either primary or secondary and may respond to dietary measures to reduce the dependence on fatty acid oxidation.

Developmental study of the gene expression for alpha and gamma subunits of enolase in the rat brain by in situ hybridization histochemistry

The gene expression for alpha and gamma subunits of enolase, a dimeric enzyme in the glycolytic pathway, was examined in the developing brain of rats by in situ hybridization. The expression for the gamma subunit of enolase was first detected in post-mitotic neurons settled in the mantle zone at E13, and it increased progressively until the adult stage. Expression signals for the alpha subunit were discerned in two discrete regions showing different developmental changes: the signals in the proliferative ventricular zone were intense at E13 and decreased and eventually disappeared around birth, whereas the signals in the mantle zone persisted until the adult stage. In the adult brain, mRNAs for the alpha and gamma subunits were expressed widely in neurons, resulting in almost similar temporal patterns in the brain except for the cerebellum. Expression levels of the alpha subunit in adult glial cells were below the detection threshold of the in situ hybridization analysis. These findings suggest that both alpha and gamma enolase subunits participate in energy production in neurons of the mature brain and that marked changes in the subunit composition of enolase occur according to both neuron type and maturation.

Mitochondrial adaptations in denervated muscle: relationship to muscle performance

We have studied mitochondrial adaptations in muscle subject to chronic denervation, and their relationship to muscle performance, using a model of unilateral sciatic nerve denervation in rats over periods of 2, 5, 8, 14, 21, 28, 35, and 42 days (n = 5-9 rats/day). Time to peak tension (TPT), one-half relaxation time (1/2RT), and endurance performance were evaluated during in situ stimulation of denervated and contralateral gastrocnemius-plantaris muscles. Denervation led to a 70% decline in muscle mass after 42 days. TPT and 1/2RT increased 17 and 30%, respectively, indicating a transformation toward slower muscle. The activities of the enzymes cytochrome-c oxidase (CYTOX), succinate dehydrogenase, and citrate synthase were decreased by 8-14 days, and by 42 days these were 34-58% of control. The mitochondrial phospholipid cardiolipin was reduced earlier, by 5 days, and gradually decreased to 37% of control. Thus phospholipid removal appears to precede the loss of enzyme activity during decreases in mitochondrial content. Endurance performance was reduced in parallel with decreases in enzyme activity and cardiolipin. Cytochrome c mRNA levels decreased to 52% of control by 5 days. Denervation resulted in coordinated changes in mRNA levels encoding the nuclear-derived CYTOX subunit VIc and the mitochondrially derived CYTOX subunit III. However, changes in CYTOX activity did not always parallel alterations in subunit mRNA levels. Thus transcriptional and translational mechanisms operate in regulating mitochondrial gene expression during denervation.

Muscle growth and composition in heavy and light breed chickens adapted to intermittent feeding

1. The effect of intermittent feeding in chickens of heavy breed (HB; meat type) and light breed (LB; egg type) on skeletal muscle growth and composition was studied in adapted and non-adapted chickens. 2. Food intake, relative to body-weight, was similar in both breeds but was higher in ad lib.-fed than in intermittently fed birds. 3. On repletion days the relative growth rate was similar in both breeds, while on depletion the LB chickens lost more weight than the HB chickens. In both breeds, the relative growth was higher in the intermittently fed birds during days of food restoration than in those fed ad lib. 4. The relative weight of the breast muscle was higher in HB birds than in LB birds, but deposition rate on the day of food restoration was similar in both breeds. This growth was more pronounced in chickens adapted to alternate feeding than in chickens exposed to this feeding regimen for one cycle. 5. Protein concentration in breast muscle was not affected by age and was slightly higher in LB chickens than in HB chickens. Soluble protein was markedly reduced on days of repletion, and more at 46 d than at 18 d of age. 6. The RNA:DNA ratio was higher in HB than in LB chickens, and lower on days of food deprivation than on days of food restoration. After repletion this ratio returned to the level of the ad lib.-fed chickens. While in LB chickens cell size (as estimated by DNA concentration) remained constant on repletion and depletion days, in the HB chickens it decreased. 7. The rapid growth of breast muscle in HB chickens was attributed to the higher rate of protein synthesis (estimated by RNA:DNA ratio) compared with LB chickens. This may also explain why the breast muscle of LB chickens was less sensitive to intermittent feeding than that of HB chickens.

Difference in thiamine metabolism between extensor digitorum longus and soleus muscles

1. Thiamine diphosphate level was higher in soleus muscle than in extensor digitorum longus muscle in various animals, whereas thiamine triphosphate level was less in the former muscle than in the latter except for mouse. 2. 2-Oxoglutarate dehydrogenase, transketolase and thiamine pyrophosphokinase activities were higher in soleus muscle than in extensor digitorum longus in rat and guinea pig. 3. The differences between rat two muscle phenotypes in thiamine diphosphate, but not thiamine triphosphate, level and the thiamine-related enzyme activities disappeared after denervation. 4. Tenotomy had little effect on thiamine phosphate levels and the thiamine-related enzyme activities in rat skeletal muscles.

Developmental changes in fiber type-related proteins in soleus, rectus femoris, and heart muscles of normal and dystrophic mice

By using sensitive enzyme immunoassay methods, several isoenzymes or isoproteins related to muscle fiber types were determined in the soleus (SOL), rectus femoris (RFM), and heart muscles of normal and dystrophic (dy/dy) mice of various ages. In normal adult mice, the S-100 protein alpha subunit (S-100 alpha) and creatine kinase B subunit (CK-B), which are known to be distributed predominantly in type I muscle fibers as S-100a0 (alpha alpha form of the S-100 protein) and the MB form of CK, respectively, were enhanced several-fold in the "aerobic" SOL muscle as compared with the "anaerobic" RFM muscle. The enolase beta subunit (beta-enolase) and the M subunit of CK (CK-M) were present in the RFM at levels increased several-fold compared to levels in the SOL of the same mice. In age-matched dystrophic adult mice, however, the compositions of these muscle-related proteins in the RFM muscle shifted to those of the SOL muscle: S-100 alpha and CK-B increased several-fold, beta-enolase and CK-M decreased markedly as compared with the normal RFM. On the other hand, the SOL and heart muscles of dystrophic mice showed only a slight increase of CK-B or decrease of CK-M. In the RFM of 3-week-old dystrophic mice, S-100 alpha and beta-enolase levels were similar to those in the RFM of control littermates, but a significant increase of CK-B and a decrease of CK-M were already observed in this early stage of dystrophy. These results indicate that changes in muscle-related proteins in the dystrophic muscles are apparently displayed mainly in the anaerobic muscles and feature a decrease in type II fiber-related proteins and a relative increase in type I fiber-related proteins. The mechanism of these changes in dystrophic mice is discussed.

Effects of denervation on spectrin concentration in avian skeletal muscle

The effect of denervation on avian muscle alpha-spectrin was examined in fast and slow muscles. Using immunofluorescence, the surgically denervated fast-twitch posterior latissimus dorsi (PLD) exhibited a significant increase in spectrin antigen associated with the sarcolemma and within the sarcoplasm compared with the contralateral innervated control muscle. Using gel electrophoresis followed by immunoblotting, we found a two- to three-fold increase in the levels of spectrin in the denervated PLD over that found in the innervated PLD. These levels were comparable to those found previously in slow and dystrophic muscle. The intrafiber distribution of spectrin is similar between the denervated PLD and the slow-tonic anterior latissimus dorsi (ALD). When spectrin was examined in dystrophic PLD muscle, denervation was found to have no effect. These results support our hypothesis that the concentration of spectrin within muscle fibers reflects the physiological state of those fibers. Changes in spectrin concentration may be a useful probe to study the various alterations in physical parameters found among fast, slow, dystrophic, and denervated fibers.

Ontogeny and estrogen responsiveness of creatine kinase and glycolytic enzymes in brain and uterus of rat

We have studied the postnatal ontogeny of creatine kinase (CK) and the glycolytic enzymes phosphoglycerate kinase (PGK), phosphoglycerate mutase (PGM), enolase (En), and pyruvate kinase (PK) in rat brain and uterus. In 30-day-old rat, brain and uterus express the fetal isoforms CK-B, PGK-A, PGM-B, En-alpha and PK-M2, and the differentiated isoforms En-gamma and PK-M1. The activity of glycolytic enzymes in uterus of two-day-old rat is as in brain, while CK activity is 3 times higher in brain. The activity of the glycolytic enzymes in brain began to increase (3-4-fold) 10 days after birth, in a coordinated manner. CK activity began to increase 5 days after birth in both brain (4.2-fold) and uterus (4.5-fold), suggesting the dissociation of glycolytic enzyme ontogeny from CK. In contrast to brain, the levels of glycolytic enzymes in uterus were highest at birth, suggesting the action of a tissue-specific mechanism for regulation of the constitutive levels of glycolytic isozymes. Except for PGM, all enzymes showed an increase in total activity, in response to estrogen, in uterus but not in whole brain.

Additional biochemical criteria in the differential diagnosis of myositis

Thirty-six biopsy specimens of human biceps and vastus lateralis muscles were examined by histometric analysis and determination of enzyme activities (phosphorylase, triosephosphate dehydrogenase, 3-hydroxacyl-CoA-dehydrogenase, lactate dehydrogenase, hexose isomerase, citrate synthetase, 6-phosphogluconate dehydrogenase). The series included 13 specimens from patients suffering from a benign form of muscular dystrophy (limb girdle and Becker type of muscular dystrophy) and 12 specimens from patients with an acute (n = 5) or chronic (n = 7) form of myositis. Muscle fibres were atrophic in myositis and hypertrophic (with an increased variation of fibre diameters) in muscular dystrophies, as has been shown previously. When myositis samples were compared with either normal or dystrophic muscles, a highly significant lowering of glycolytic enzyme activity was found in chronic myositis, while the activity of 6-phosphogluconate dehydrogenase was elevated to highly significant levels. Measurements of the latter enzyme's activity might be of additional value in differentiating chronic forms of myositis from benign muscular dystrophies.

Regulation of taurine transport in rat skeletal muscle

Taurine concentration of soleus muscle (SL, slow-twitch) was initially about twofold higher than that of extensor digitorum longus muscle (EDL, fast-twitch). Taurine concentration in gastrocnemius muscle (GC) was intermediate between that of EDL and SL. Four days after sciatic nerve section, taurine concentration in the EDL but not in the SL was increased by 2.5-fold. The increase was not due to the muscle atrophy and was observed 28 days after denervation. Tenotomy did not increase the total taurine content of the EDL. The increase in taurine concentration of the denervated EDL was prevented by simultaneous ingestion of guanidinoethane sulfonate, a competitive inhibitor of taurine transport. The initial and the maximal rates of [3H]taurine uptake were significantly higher in SL than in EDL. Denervation dramatically accelerated the initial and the maximal rates of the transport in EDL, whereas it significantly reduced those in SL. In contrast, the electrical stimulation of sciatic nerve accelerated the uptake of taurine by EDL and SL of the control but not of the curare-treated rats. These results suggest that transport of taurine into rat skeletal muscles is regulated differently by neural information and by muscular activity, and that the regulation is dependent on the muscle phenotype.

Glyceraldehyde-3-phosphate dehydrogenase mRNA. Activity and amount in dystrophic hamster muscle

The activity and amount of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in muscle of young dystrophic hamsters was reduced to approximately half the level found in control animals. No changes in brain or liver enzyme activity were found. Several other glycolytic enzyme activities and creatine kinase activity in muscle were unchanged, except for modest decreases in aldolase and pyruvate kinase. To assess the synthesis of glyceraldehyde-3-phosphate dehydrogenase, the poly(A)+ RNA was isolated from muscle polysomes of dystrophic and control animals and its activity was assessed in an mRNA-dependent translation system. The translatability of the mRNA for GAPDH found in the dystrophic muscle preparations also was half of that found in the control muscle preparations. Decreases were also found in the translatability of mRNA for tropomyosin.

Differential effect of denervation on free-radical scavenging enzymes in slow and fast muscle of rat

To determine the effect of denervation on the free-radical scavenging systems in relation to the mitochondrial oxidative metabolism in the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles, the sciatic nerve of the rat was crushed in the midthigh region and the muscle tissue levels of five enzymes were studied 2 and 5 weeks following crush. Recently developed radioimmunoassays were utilized for the selective measurement of cuprozinc (cytosolic) and mangano (mitochondrial) superoxide dismutases. Total tissue content of cuprozinc superoxide dismutase showed a mild decrease after denervation in slow but not in fast muscle. Manganosuperoxide dismutase and fumarase decreased markedly at 2 weeks and returned toward control levels by 5 weeks, the changes appearing to be greater in slow than in fast muscle. At 2 weeks, cytochrome c oxidase decreased significantly in slow, but not in fast muscle. GSH-peroxidase at baseline was 10-fold higher in slow than in fast muscle, markedly decreased at 2 weeks in slow muscle, and returned toward control levels at 5 weeks, whereas the total enzyme activity in fast muscle did not change through 5 weeks. These data represent the first systematic report of free radical scavenging systems in slow and fast muscles in response to denervation. Selective modification of cuprozinc and manganosuperoxide dismutases and differential regulation of GSH-peroxidase was demonstrated in slow and fast muscle.

Effect of denervation on glucose uptake in rat soleus and extensor digitorum longus muscles

From 1 to 14 days after denervation, glucose uptake in the fast extensor digitorum longus and slow soleus muscles in rats was investigated and compared with that of the corresponding intact contralateral muscles. Denervation-induced atrophy in soleus was greater than that in extensor digitorum longus muscle. Glucose uptake in extensor digitorum longus muscle increased significantly, but that in soleus decreased significantly.

Content and synthesis of glycolytic enzymes and creatine kinase in skeletal muscles and normal and dystrophic chickens

A number of workers have reported that avian muscular dystrophy causes alterations in the levels of certain enzyme activities in "fast-twitch" muscle fibers but has little effect on enzyme activities in "slow-twitch" muscle fibers. In the present work, the effects of this disease on the content and relative rates of synthesis of a number of glycolytic enzymes and the skeletal muscle-specific MM isoenzyme of creatine kinase in chicken muscles was investigated. It was shown that (i) the approximate 50% reductions in steady-state concentrations of three glycolytic enzymes (aldolase, enolase, and glyceraldehyde-3-P dehydrogenase) in dystrophic breast (fast-twitch) muscle result predominantly from decreases in relative rates of synthesis, rather than accelerations in relative rates of degradation, of these proteins in the diseased tissue; (ii) in contrast to the situation with the glycolytic enzymes, muscular dystrophy has only minor effects (25% or less) on the content and relative rate of synthesis of MM creatine kinase in breast muscle fibers; (iii) the muscular dystrophy-associated alterations in content and synthesis of the glycolytic enzymes in breast muscle fibers become apparent only during postembryonic maturation of this tissue; and (iv) as expected, muscular dystrophy has no significant effect on the content or relative rates of synthesis of glycolytic enzymes in slow-twitch lateral adductor muscles of the chicken. These results are discussed in terms of the apparent similarities between the effects of muscular dystrophy and surgical denervation on the protein synthetic programs expressed by mature fast-twitch muscle fibers.

Effect of denervation on the glycolytic metabolism of the main electric organ of Electrophorus electricus (L.)

Biochemical modifications of the glycolytic metabolism of the electric organ of Electrophorus electricus (L.) have been studied as a function of denervation. The activities of LDH, MDH and the concentrations of ATP, lactic and pyruvic acids were measured at intervals of zero, 15, 30 and 60 days following denervation. In parallel, CPK activity was also measured. All of these biochemical characteristics were substantially altered by denervation. The results obtained point to a change, after 15 days of denervation, from the normal anaerobic to an aerobic metabolism which remains after 30 days and reverts to anaerobic at 60 days.

Altered rat skeletal muscle carnitine with age and after denervation

We investigated the effect of denervation on the concentration of total free, and acyl carnitine in the soleus (S), extensor digitorum longus (EDL), and anterior tibial (AT) muscles of the rat. Soon after denervation there was a marked decrease in total carnitine in all three muscles. Acyl carnitine levels decreased concomitantly with changes in total carnitine. In control but not in denervated muscle, the carnitine concentration was age-dependent during the period of rapid growth of the animals. The highest carnitine concentration was observed at 14 weeks of age. The results of this study suggest that normal innervation significantly influences carnitine-mediated lipid metabolism in skeletal muscle.

Content and synthesis of several abundant glycolytic enzymes in skeletal muscles of normal and dystrophic mice

In both 2- and 3-month-old 129 ReJ mice, the catalytic activity levels of three enzymes involved in glycogen breakdown (phosphorylase, enolase, and aldolase) were found to be 35-50% lower in hind limb muscles of dystrophic mice as compared with normal mice. The reduced activities of these enzymes in the diseased tissue was directly due to corresponding reductions in the number of enzyme molecules rather than being due to inactivation of the enzymes in the dystrophic muscle. Results of short term double isotope incorporation experiments conducted with muscle explants in vitro suggested that the rates of synthesis of these enzymes, and of most other abundant cytosolic proteins, relative to each other, were similar in hind limb muscles of normal and dystrophic mice. The present work on murine muscular dystrophy is discussed in terms of our previous studies into the influence of avian muscular dystrophy on the content and synthesis of abundant glycolytic enzymes in chicken skeletal muscles.

Similarities in properties, content, and relative rates of synthesis of fructose-P2 aldolase in livers of fed and starved rats

The present work gives evidence that, in contrast to the situation reported by Pontremoli et al. for the rabbit (Proc, Natl. Acad. Sci. U.S.A. 76, 6323-6325, 1979; Arch. Biochem. Biophys. 203, 390-394, 1980; Proc. Natl. Acad. Sci. U.S.A, 79, 5194-5196, 1982), starvation for as long as 3 days does not cause intracellular covalent modification and inactivation of fructose-P2 aldolase molecules in rat liver cells. This conclusion is based on our observations that liver aldolase molecules isolated from fed and starved rats in the presence of proteolytic inhibitors were not distinguished on the basis of specific catalytic activity, electrophoretic mobility, subunit molecular weight, NH2-terminal structure, or COOH-terminal structure. Further, the approximate 40% loss in rat liver mass which occurred during the 3-day fast was not associated with appreciable changes in the content of aldolase and most other abundant cytosolic proteins per gram of rat liver, as judged by electrophoretic analysis of 100 000-g soluble fractions of liver extracts. Finally, a 3-day fast had no appreciable effect on the relative rates of synthesis of aldolase and most other abundant cytosolic proteins in rat liver. Our findings suggest that nutrient deprivation has no preferential effect on the concentration or metabolism of aldolase in rat liver cells.

Cloning and sequencing of a deoxyribonucleic acid copy of glyceraldehyde-3-phosphate dehydrogenase messenger ribonucleic acid isolated from chicken muscle

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was purified from the breast muscles of 3-week-old chickens and used to raise a specific antiserum in rabbits. This antiserum was coupled to an in vitro translation assay to monitor the purification of GAPDH mRNA. RNA was isolated from identical breast muscles and consecutively fractionated with several techniques to yield a preparation of GAPDH mRNA which was at least 50% pure. Double-stranded cDNA was made against this purified RNA, inserted into pBR322, and used to transform Escherichia coli. Recombinants were screened by colony filter hybridization with a cDNA probe made against the purified RNA. The hybridization-positive clone with the largest insert, pGAD-28, was then characterized by using pGAD-28-cellulose to select complementary RNA from total poly(A) RNA and then translating the hybridization-selected RNA in vitro. The single translation product was shown to be GAPDH by (1) comigration with pure GAPDH on sodium dodecyl sulfate-polyacrylamide gels, (2) precipitation with specific anti-GAPDH antiserum, (3) cyanylation fingerprinting, and (4) AMP-agarose affinity chromatography. pGAD-28 was mapped with several restriction enzymes and then sequenced by the method of Maxam and Gilbert [Maxam, A. M., & Gilbert, W. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 560]. The 1261-nucleotide insert was found to contain 29 nucleotides of noncoding sequence at the 5' end, the entire coding region, and 230 nucleotides of the 3'-noncoding region including a poly(A) addition signal (AATAAA) and the first five residues of the poly(A) tail.

Effect of tetrodotoxin relaxation of cultured skeletal muscle on the sarcoplasmic reticulum Ca2+-transport ATPase

The spontaneous contractions of cultured chick skeletal muscle fibers were abolished by growth of cultures in the presence of tetrodotoxin (TTX). Inhibition of the contractile activity of cultured myofibers was associated with a marked reduction in the rate of azide-insensitive, ATP-dependent Ca2+ uptake by the total particulate fraction of cell homogenates and by purified sarcoplasmic reticulum. Myosin heavy chain (MHC) accumulation and azide-insensitive, ATP-dependent Ca2+ uptake into a total cell membrane fraction were measured simultaneously in the same culture dish. A decrease in the activity of the ATP-dependent Ca2+ uptake system preceded a significant reduction in MHC content of contraction-inhibited cultures. The reduced rate of Ca2+ uptake observed in the sarcoplasmic reticulum from TTX-treated cultures paralleled a decrease in the amount of enzymatically active Ca2+-transport ATPase. The cellular concentration of the ATPase was estimated from a measurement of the concentration of the Ca2+-dependent, hydroxylamine-sensitive, steady state level of phosphorylated intermediate formed in culture microsomes. In contrast to the changes observed in activity of the sarcoplasmic reticulum ATPase and MHC content of TTX-treated cultures, neither the specific activity of creatine kinase nor the accumulation of the MM isoenzyme were affected. It is therefore concluded that the contractile activity of muscle has a selective effect on the maintenance of the adult skeletal muscle phenotype.

Effect of denervation and reinnervation on oxidation of [6-14C]glucose by rat skeletal muscle homogenates

We studied the effects of denervation and reinnervation of the rat extensor digitorum longus muscle (EDL) on the oxidation of [6-14C]glucose to 14CO2. The rate of 14CO2 production decreased dramatically following denervation, and the decrease became significant 20 days after nerve section. Prior to day 20, changes apparently reflected the decline of muscle mass. Decreased 14CO2 production was due to reduced capacity of the enzymatic system (apparent Vmax); there was no change in apparent affinity for glucose (apparent Km). Mixing experiments revealed that the loss of oxidative capacity following denervation is not caused by production of soluble inhibitors by degenerating muscle. Oxidative metabolism, as measured by 14CO2 evolution, recovered during reinnervation. Surprisingly, the specific activity in reinnervated muscles displayed an "overshoot" of approximately 50%, which returned to control by day 60, possibly reflecting increased energy demand by the growing muscle. The time-course of the denervation-mediated change indicates that altered oxidative capacity is secondary to events that initiate denervation changes in muscle. Nevertheless, diminished oxidative capacity may be of considerable metabolic significance in denervated muscle.