Muscle glycolysis stimulation

In muscle, epinephrine stimulates glycogen breakdown and glycolysis, providing ATP to support contraction. 

Epinephrine increases muscle glycolysis, and therefore blood lactic acid production and an amplified Cori cycle. In the liver, epinephrine stimulates gluconeogenesis and blood glucose will therefore rise. 

Reflect and Apply How is it possible that both insulin and epinephrine stimulate muscle glycolysis ... 

In 1937 Krebs found that citrate could be formed in muscle suspensions if oxaloacetate and either pyruvate or acetate were added. He saw that he now had a cycle, not a simple pathway, and that addition of any of the intermediates could generate all of the others. The existence of a cycle, together with the entry of pyruvate into the cycle in the synthesis of citrate, provided a clear explanation for the accelerating properties of succinate, fumarate, and malate. If all these intermediates led to oxaloacetate, which combined with pyruvate from glycolysis, they could stimulate the oxidation of many substances besides themselves. (Kreb s conceptual leap to a cycle was not his first. Together with medical student Kurt Henseleit, he had already elucidated the details of the urea cycle in 1932.) The complete tricarboxylic acid (Krebs) cycle, as it is now understood, is shown in Figure 20.4. 

Spriet, L.L., Soderlund, K., Bergstrom, M., Hultman, E. (1987b). Skeletal muscle glycogenolysis, glycolysis, and pH during electrical stimulation in men. J. Appl. Physiol. 62, 616-621. 

Nutrient homeostasis cell uptake of glucose (especially important in adipose and muscle), amino acids (all cells) and fatty acids stimulation of glycolysis but inhibition of gluconeogenesis (liver), synthesis of glycogen (liver and muscle), triglyceride (liver and adipose) and protein (all cells) ... 

Figure 22.17 Summary of mechanisms to maintain the ATP/ADP concentration ratio in hypoxic myocardium. A decrease in the ATP/ADP concentration ratio increases the concentrations of AMP and phosphate, which stimulate conversion of glycogen/ glucose to lactic acid and hence ATP generation from glycolysis. The changes also increase the activity of AMP deaminase, which increases the formation and hence the concentration of adenosine. The latter has two major effects, (i) It relaxes smooth muscle in the arterioles, which results in vasodilation that provides more oxygen for aerobic ATP generation (oxidative phosphorylation). (ii) It results in decreased work by the heart (i.e. decrease in contractile activity), (mechanisms given in the text) which decreases ATP utilisation.

In 1929, Fiske and Subbarow,d/f h curious about the occurrence of purine compounds in muscle extracts, discovered and characterized ATP. It was soon shown (largely through the work of Lundsgaard and Lohman)f that hydrolysis of ATP provided energy for muscular contraction. At about the same time, it was learned that synthesis of ATP accompanied glycolysis. That ATP could also be formed as a result of electron transport became clear following an observation of Engelhardth i in 1930, that methylene blue stimulated ATP synthesis by tissues. 

In fast white fibers, glycolysis catabolizes glucose. The relative lack of mitochondria in these fibers causes the white appearance. The rapid breakdown of glucose by anaerobic metabolism means that ATP is made rapidly. These muscles are used in rapid, short-duration movement and exhibit a fast twitch when electrically stimulated. The flight muscles of birds are of this type—remember that you find the white meat of a chicken on the breast. 

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