Development of acetylcholine sensitivity in cultured skeletal muscle

Résumé Nous avons étudié in vitro la réaction des fibres musculaires, à l'action de l'acétylcholine, de la tubocurarine et du décaméthonium. L'acétylcholine a provoqué une contraction un peu après la fusion des myoblastes, avant que les fibres ne deviennent striées. La sensibilité des fibres à l'acétylcholine a augmenté avec le développement morphologique. Elle s'est manifestée le long des fibres et les drogues de blocage neuromusculaire ont agi comme prévu.     

Glutaminase activity in rat skeletal muscle mitochondria

Summary Isolated rat skeletal muscle mitochondria took up about 40-ng-atoms O per min per mg protein, with glutamine as the only respiratory substrate. The mitochondria incubated in the presence of glutamine and KCN formed both ammonia and glutamate in equivalent amounts. The experiments reported here provide suggestive evidence that rat skeletal muscle mitochondria contain glutaminase (L-glutamine amidohydrolase EC 3.5.1.2.) activity.This work was supported by the Polish Academy of Sciences within the project II. 1, 2, 6.     

Glutaminase activity in rat skeletal muscle mitochondria

Isolated rat skeletal muscle mitochondria took up about 40-ng-atoms O per mg protein, with glutamine as the only respiratory substrate. The mitochondria incubated in the presence of glutamine and KCN formed both ammonia and glutamate in equivalent amounts. The experiments reported here provide suggestive evidence that rat skeletal muscle mitochondria contain glutaminase (L-glutamine amidohydrolase EC 3.5.1.2.) activity.     

Alkaline phosphatase activity in normal and denervated skeletal muscle

Summary Changes in the specific activity of alkaline phosphatase in the normal and denervated skeletal muscle have been studied both histochemically as well as biochemically for a maximum period of 8 weeks of its postnatal development. In the normal muscle, a heterogenous population of fibres with respect to the enzyme distribution is observed. Relatively higher levels of enzyme in the denervated muscle and also the proliferation of extrafibrillar connective tissue in the diseased muscle show its specific association with the lytic processes.     

Effect of fasting on skeletal muscle triglyceride content

The effect of prolonged food deprivation on the triglyceride level in different types of skeletal muscle was studied in the rat. It has been found that fasting gradually reduces the triglyceride content in each muscle type. It is concluded that i.m. triglycerides play an important role as energy fuel during fasting.     

Effect of fasting on skeletal muscle triglyceride content

Summary The effect of prolonged food deprivation on the triglyceride level in different types of skeletal muscle was studied in the rat. It has been found that fasting gradually reduces the triglyceride content in each muscle type. It is concluded that i.m. triglycerides play an important role as energy fuel during fasting.     

The response of human skeletal muscle tissue to hypoxia

Hypoxia refers to environmental or clinical settings that potentially threaten tissue oxygen homeostasis. One unique aspect of skeletal muscle is that, in addition to hypoxia, oxygen balance in this tissue may be further compromised when exercise is superimposed on hypoxia. This review focuses on the cellular and molecular responses of human skeletal muscle to acute and chronic hypoxia, with emphasis on physical exercise and training. Based on published work, it is suggested that hypoxia does not appear to promote angiogenesis or to greatly alter oxidative enzymes in skeletal muscle at rest. Although the HIF-1 pathway in skeletal muscle is still poorly documented, emerging evidence suggests that muscle HIF-1 signaling is only activated to a minor degree by hypoxia. On the other hand, combining hypoxia with exercise appears to improve some aspects of muscle O₂ transport and/or metabolism.     

Cholinesterase activity in skeletal muscle after botulinum toxin

Zusammenfassung Bei Zufuhr von Botulinum-A-Toxin in den Muskel Tibialis anterior der Ratte war die Cholinesteraseaktivität nach zwei Wochen herabgesetzt, jedoch weniger ausgesprochen als nach zweiwöchiger Denervierung des Muskels.     

Catalase activity in skeletal muscle of varying fibre types

Summary Slow oxidative skeletal muscles of rats and hamsters exhibit significantly greater catalase activity than fast oxidative muscles. Furthermore, regions of a single muscle may vary significantly.     

Developmental forms of human skeletal muscle AMP-deaminase

Chromatography on phosphocellulose revealed the existence of two well-separable forms of skeletal muscle AMP-deaminase in the tissue extracts of 11- and 16-week-old human fetuses. One of these forms elutes from the column at the same salt concentration as the muscle isozyme found in the skeletal muscle extract from adult man, and seems to have similar kinetic properties. The second form, which was found only in vestigial amounts in adult human tissue extract, represents different kinetic properties and seems to be a form characteristic for the fetal period of ontogenesis.     

Increased hexokinase activity in red and white skeletal muscle after denervation

Resumen La actividad de la hexoquinasa es mayor en el músculo rojo que en el blanco, y ésta aumenta como resultado de la denervación. Tales resultados son lo opuesto de los observados para la mayoría de las enzimas glicolíticas. Estos son explicables si una de las isoenzimas de la hexoquinasa se encuentra localizada dentro del tejido conjunctivo del músculo esquelético.     

Effect of exercise on ribonuclease activity in rat skeletal muscle

Summary Distribution of ribonuclease activity (measured at pH 7.6) in subcellular fractions of homogenates of rat skeletal muscle was investigated in sedentary animals and after 8 weeks running program. Training increased ribonuclease activity (expressed as units of enzyme per g of muscle protein). There was no increase in nuclear fraction, but in both cytoplasmic and mitochondrial fractions the RNA-ase activity increased 42% and 45% respectively.Acknowledgments. I would like to thank Prof. L. elewski and Dr J. Popinigis for helpful suggestions.     

Insulin action in cultured human skeletal muscle cells during differentiation: assessment of cell surface GLUT4 and GLUT1 content

In mature human skeletal muscle, insulin-stimulated glucose transport is mediated primarily via the GLUT4 glucose transporter. However, in contrast to mature skeletal muscle, cultured muscle expresses significant levels of the GLUT1 glucose transporter. To assess the relative contribution of these two glucose transporters, we used a novel photolabelling techniques to assess the cell surface abundance of GLUT1 and GLUT4 specifically in primary cultures of human skeletal muscle. We demonstrate that insulin-stimulated glucose transport in cultured human skeletal muscle is mediated by GLUT4, as no effect on GLUT1 appearance at the plasma membrane was noted. Furthermore, GLUT4 mRNA and protein increased twofold (p < 0.05), after differentiation, whereas GLUT1 mRNA and protein decreased 55% (p < 0.005). Incubation of differentiated human skeletal muscle cells with a non-peptide insulin mimetic significantly (p < 0.05) increased glucose uptake and glycogen synthesis. Thus, cultured myotubes are a useful tool to facilitate biological and molecular validation of novel pharmacological agents aimed to improve glucose metabolism in skeletal muscle.