Distribution in muscle and liver vein protein of 15N administered as ammonium acetate to man.

Fürst, Peter; Jönsson, Ann-Cathrine; Josephson, Bertil; Vinnars, E.

doi:10.1152/jappl.1970.29.3.307

Cited by 34 publications

(10 citation statements)

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“…Lactate production was calculated by assuming that it was equivalent to the protons required to produce the observed change of pH, making further assumptions about the concentrations and dissociation constants of the intracellular buffers. These buffers were taken to be: (a) protein‐bound histidine, 56 m m , p K = 6.8 (Fürst et al 1970); (b) bicarbonate, 10 m m , p K = 6.1 (Sahlin et al 1977); (c) carnosine, 7 m m , p K = 6.8 (Mannion et al 1992); and (d) phosphate, added to the computation according to the phosphate measured by MRS (p K = 6.73). The non‐phosphate buffer capacity came to 34.5 slykes, and this increased to approximately 50 slykes when P i reached its highest levels in the fatigued muscles.…”

Section: Methodsmentioning

confidence: 99%

Energy turnover in relation to slowing of contractile properties during fatiguing contractions of the human anterior tibialis muscle

Jones

Turner

McIntyre

et al. 2009

The Journal of Physiology

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Slowing and loss of muscle power are major factors limiting physical performance but little is known about the molecular mechanisms involved. The slowing might be a consequence of slow detachment of cross bridges and, if this were the case, then a reduction in the ATP cost of an isometric contraction would be expected as the muscle fatigued. The human anterior tibialis muscle was stimulated repeatedly under ischaemic conditions at 50 Hz for 1.6 s with a 50% duty cycle and muscle metabolites measured by 31 P magnetic resonance spectroscopy. Over the course of 20 contractions the half-time of relaxation increased from 36.5 ± 0.09 ms (mean ± s.e.m.) to 113 ± 17 ms and isometric force was reduced to 63 ± 3% of the initial value. ATP turnover was determined from the change in high energy phosphates and lactate production, the latter estimated from the change of intracellular pH. ATP turnover over the first three contractions was 2.45 ± 0.09 mm s −1 and decreased to 1.8 ± 0.06 mm s −1 over the last five tetani. However, when this latter value was normalised for the decrease in isometric force, it became 2.56 ± 0.3 mm s −1 , which is the same as the turnover of the fresh muscle. The data suggest that the rate of cross bridge detachment is unaffected by fatigue and are consistent the suggestion that it is the rate of attachment which is slowed rather than the rate of detachment. The present results focus attention on stages in the cross bridge cycle concerned with attachment and the transition from low to high force states that may be influenced by metabolic changes in the fatiguing muscle.

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Section: Methodsmentioning

confidence: 99%

Energy turnover in relation to slowing of contractile properties during fatiguing contractions of the human anterior tibialis muscle

Jones

Turner

McIntyre

et al. 2009

The Journal of Physiology

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“…From our results, we can calculate that the protein buffering capacity was ∼52 mmol H + ·kg muscle d.w. −1 ·pH −1 (30-35%) for both male triathletes and male team-sport athletes in the present study. This value closely approximates the value of 50 mmol H + ·kg muscle d.w. −1 ·pH −1 that can be calculated from the reported histidine concentration in human muscle protein (2.7 g/100 g of protein; [16]), the protein content in muscle tissue (∼170 g·kg w.w. −1 ; [17]) and the pKa value of the imidazole ring in protein-bound histidine residues (6.25; [42]). These calculations however, must be treated with caution as theoretical calculations of the buffering power of proteinbound histidine residues are complicated by uncertainty regarding the pKa value of histidine (5.97 at 37°C) when incorporated into proteins [6].…”

Section: βM In Vitromentioning

confidence: 99%

High-intensity exercise decreases muscle buffer capacity via a decrease in protein buffering in human skeletal muscle

Bishop

Edge

Méndez-Villanueva

et al. 2009

Pflugers Arch - Eur J Physiol

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We have previously reported an acute decrease in muscle buffer capacity (betam(in vitro)) following high-intensity exercise. The aim of this study was to identify which muscle buffers are affected by acute exercise and the effects of exercise type and a training intervention on these changes. Whole muscle and non-protein betam(in vitro) were measured in male endurance athletes (VO(2max) = 59.8 +/- 5.8 mL kg(-1) min(-1)), and before and after training in male, team-sport athletes (VO(2max) = 55.6 +/- 5.5 mL kg(-1) min(-1)). Biopsies were obtained at rest and immediately after either time-to-fatigue at 120% VO(2max) (endurance athletes) or repeated sprints (team-sport athletes). High-intensity exercise was associated with a significant decrease in betam(in vitro) in endurance-trained males (146 +/- 9 to 138 +/- 7 mmol H(+) x kg d.w.(-1) x pH(-1)), and in male team-sport athletes both before (139 +/- 9 to 131 +/- 7 mmol H(+) x kg d.w.(-1) x pH(-1)) and after training (152 +/- 11 to 142 +/- 9 mmol H(+) x kg d.w.(-1) x pH(-1)). There were no acute changes in non-protein buffering capacity. There was a significant increase in betam(in vitro) following training, but this did not alter the post-exercise decrease in betam(in vitro). In conclusion, high-intensity exercise decreased betam(in vitro) independent of exercise type or an interval-training intervention; this was largely explained by a decrease in protein buffering. These findings have important implications when examining training-induced changes in betam(in vitro). Resting and post-exercise muscle samples cannot be used interchangeably to determine betam(in vitro), and researchers must ensure that post-training measurements of betam(in vitro) are not influenced by an acute decrease caused by the final training bout.

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“…In adults, on an intake of about 70 g protein/d, when NH3 is given orally, label is predominantly incorporated into urea, but there is also ready exchange with glutamate and through serine-glycine interaction (Jackson & Golden, 1981;Nissim et al 1981). On lower protein intakes, or when the label is given intravenously, the rate of incorporation into proteins is greatly increased (Furst et al 1969(Furst et al , 1970. The movement of label around other amino acids is directly related to their ability to engage in N-exchange reactions, which is variable, and strictly limited for the essential (indispensable) amino acids (Aqvist, 1951).…”

Section: Nitrogen F O R the Microfloramentioning

confidence: 99%

Salvage of urea-nitrogen and protein requirements

Jackson

1995

Proc. Nutr. Soc.

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The metabolism of N in the colon is dominated in quantitative terms by the metabolic activity of the microflora. The microflora are not found exclusively in the colon, as there are increasing numbers in the terminal ileum towards the ileocaecal valve; however, the working approximation is that functionally significant activity is colonic. There is a complex, and as yet inadequately defined, interaction of the luminal, mucosal and intramucosal populations of bacteria which is almost certainly of functional relevance. As for all organisms, the metabolic profile of the microflora is determined by the availability of substrate, which gives rise to an interdependence of protein, amino acid and N metabolism with the availability of energy; but for the practical purposes of the present analysis the reasonable assumption has been made that for all the work quoted, energy and other nutrients are not limiting.In general bacteria utilize NH3 as their preferred source of N, and other forms of protein or amino acids are reduced to NH3 before being used metabolically. The microflora represent a complex ecosystem, with aspects of a continuous-flow culture.

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Distribution in muscle and liver vein protein of 15N administered as ammonium acetate to man.

Cited by 34 publications

References 0 publications

Energy turnover in relation to slowing of contractile properties during fatiguing contractions of the human anterior tibialis muscle

Energy turnover in relation to slowing of contractile properties during fatiguing contractions of the human anterior tibialis muscle

High-intensity exercise decreases muscle buffer capacity via a decrease in protein buffering in human skeletal muscle

Salvage of urea-nitrogen and protein requirements

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