Isolated Epitrochlearis Muscles Research Articles

The effect of fructose 2,6-bisphosphate on muscle fructose-1,6-bisphosphatase activity

Rat and rabbit muscle fructose 1,6-bisphosphatase ( d-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) are inhibited by fructose 2,6-bisphosphate. In contrast with the liver isozyme, the inhibition of muscle fructose-1,6-bisphosphatase by fructose 2,6-bisphosphate is not synergistic with that of AMP, Activation of fructose-1,6-bisphosphatase by fructose 2,6-bisphosphate has been observed at high concentrations of substrate. An attempt is made to correlate changes in concentrations of hexose monophosphate, fructose 1,6-bisphosphate and fructose 2,6-bisphosphate with changes in fluxes through 6-phosphofructokinase and fructose-1,6-bisphosphatase in isolated epitrochlearis muscle challenged with insulin and adrenaline.

Muscle protein turnover: effects of exercise training and renal insufficiency.

Chronic renal failure is associated with an enhanced catabolism of muscle protein. To determine the effect of exercise training and moderate renal insufficiency on net protein catabolism and protein synthesis in isolated epitrochlearis muscles, three-fourth nephrectomized and control rats were exercise trained or remained sedentary. Net muscle protein degradation was determined by measuring the rates of release of phenylalanine and tyrosine. Protein synthesis was determined by measuring the incorporation of [U-14C]phenylalanine into muscle protein. Exercise training reduced the elevated protein degradation of uremia to control levels. In control rats, exercise training had no effect on protein degradation. Exercise training increased alanine release in control rats but did not further increase the elevated alanine release of uremia. Protein synthesis was unaffected by both uremia and exercise training. Exercise training in control and uremic rats moderately increased the responsiveness of muscle to insulin by reducing net protein degradation but did not further enhance the insulin-stimulated increase in protein synthesis. Thus exercise training ameliorates the enhanced muscle protein degradation of moderate renal insufficiency.

Muscle glutamine production in diabetic ketoacidotic rats.

The mechanism of activation of glutamine production by the hindlimb during diabetic ketoacidosis (DKA) was investigated in rats. Muscle glutamine production was estimated to account for over 90% of the total glutamine produced by the hindlimb. DKA produced significant increases in the concentrations of NH4+ and IMP in hindlimb muscles, suggesting that AMP deaminase is activated by DKA. NH4Cl- and HCl-induced acidosis did not produce these changes, indicating either that acidosis itself is not the stimulus for increased AMP deaminase activity or that the more severe degree of acidosis accompanying DKA is necessary for activation. Muscle glutamine concentrations were depressed in DKA. Experiments with isolated epitrochlearis muscle showed that the transport and permeability properties of the muscle cells (as judged by uptake and release of alpha-aminoisobutyrate and glutamine) were not altered by DKA. However, glutamine uptake by muscle cells was significantly inhibited by L-leucine, the concentration of which, along with other branched-chain amino acids, is markedly elevated in DKA.