Lactate muscle

Figure 4.23 illustrates the patterns tif metabolism in the liver In muscle, the directions of nutrient Eux at points (1) and (3) are opposite those shown that is, glucose derived from the bloodstream is converted to G-6-I then to pyruvate. TTiis pyruvate can then be completely oxidi2ed in the mitochondria or can enter the bloodstream in the form of lactate. Muscle does not contain glucose-6 phosphatase and thus cannot export glucose units stored as muscle glycogen. 

E.g.—(a) Co-dehydrogenase I systems dehydrogenases of malate, fumarate, glucose (liver), and lactate (muscle). (6) Co-dehydrogenase n systems dehydrogenase of hexose phosphate (yeast and red blood cells). 

Lactate dehydrogenase (from dogfish. Beef muscle)... 

FIGURE 19.30 (a) Pyruvate reduction to ethanol in yeast provides a means for regenerating NAD consumed in the glyceraldehyde-3-P dehydrogenase reaction, (b) In oxygen-depleted muscle, NAD is regenerated in the lactate dehydrogenase reaction. 

Lactate, a product of glucose catabolism in oxygen-starved muscles, can be converted into pyruvate by oxidation. What coenzyme do you think is needed Write the equation in the normal biochemical format using a curved arrow. 

Jervis used porous silica coated with chemisorbed polyacrylhydrazide for immobilization of adenosine monophosphate (AMP) [117]. After periodate oxidation of its ribose residue the ligand was coupled to the carrier and used for isolation of lactate dehydrogenase from rabbit muscle. The specific capacity was 2 mg of protein/g adsorbent with a ligand content of 10 pmol/g, whereas recovery of enzymatic activity after elution was 85%. Hipwell et al. [118] found that for effective binding of lactate dehydrogenases on AMP-o-aminoalkyl-Sepharose the spacer arm length required at least 4 methylene links. Apparently, a macromolecule of polyacrylhydrazide acts itself like an extended spacer arm and thus allow AMP to bind the enzyme. 

Metformin restrains hepatic glucose production principally by suppression of gluconeogenesis. The mechanisms involve potentiation of insulin action and decreased hepatic extraction of certain gluconeogenic substrates such as lactate. In addition, metformin reduces the rate of hepatic glycogenolysis and decreases the activity of hepatic glucose-6-phosphatase. Insulin-stimulated glucose uptake and glycogenesis by skeletal muscle is increased by metformin mainly by increased... 

The skeletal muscle relaxants are contraindicated in patients with known hypersensitivity. Baclofen is contraindicated in skeletal muscle spasms caused by rheumatic disorders. Carisoprodol is contraindicated in patients with a known hypersensitivity to meprobamate. Cyclobenzaprine is contraindicated in patients with a recent myocardial infarction, cardiac conduction disorders, and hyperthyroidism, hi addition, cyclobenzaprine is contraindicated within 14 days of the administration of a monoamine oxidase inhibitor. Oral dantrolene is contraindicated in patients with active hepatic disease and muscle spasm caused by rheumatic disorders and during lactation. See Chapter 30 for information on diazepam. 

Figure 2. Force generation and energy metabolism in human quadriceps femoris muscle stimulated intermittently at 20 Hz, with 1.6 sec tetani with 1.6 sec rest periods between tetani. The upper panel shows force, ATP turnover rate, and pH the middle panel, the concentrations of PCr, P and lactate and the lower panel, ATP, ADP, IMP, H, and calculated H2PO4. From Hultman et al. (1990), with permission from Human Kinetics Publishers.

Figure 5. The relationships between force generation and calculated concentration of H2PO4 (closed circles) and between force and lactate content (open circles) in the stimulated muscle presented in Figure 2. Corresponding relationships are also presented for the muscle during a 3 min recovery period (small closed and open circles). In the recovery period, the muscle was stimulated at 20 Hz for 1.6 sec at 30 sec and at one, two, and three min after the fatiguing contraction. From Hultman et al. (1990), with permission from Human Kinetics Publishers.

Juel, C. (1988), Intracellular pH recovery and lactate efflux in mouse soleus muscles stimulated in vitro The involvement of sodium/proton exchange and a lactate carrier. Acta Physiol. Scand. 132,... 

Karlsson, J. Saltin, B. (1970). Lactate. ATP, and CP in working muscles during exhaustive exercise in man. J. Appl. Physiol. 29, 598-602. 

Glycogenosis type VIII (phosphorylase b kinase deficiency) gives rise to myopathy and liver disease, either singly or in combination. Phosphorylase b kinase (PBK) converts the inactive b form of both muscle and liver phosphorylases to the active a forms of the enzymes. The ischemic lactate test sometimes shows a flat result as in McArdle s disease, but is more likely to be normal. Histochemical demonstration of myophosphorylase activity in tissue sections shows a near-normal reaction due to the presence of phosphorylase a. Accumulation of glycogen is modest and found mainly in type 2 (fast-twitch glycolytic) muscle fibers. 

Skeletal muscle utilizes glucose as a fuel, forming both lactate and CO2. It stores glycogen as a fuel for its use in muscular contraction and synthesizes muscle protein from plasma amino acids. Muscle accounts for approximately 50% of body mass and consequently represents a considerable store of protein that can be drawn upon to supply amino acids for gluconeogenesis in starvation. 

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