The rate constant of the -adenosine triphosphate to -adenosine diphosphate conversion was measured using 31 P nuclear magnetic resonance magnetization transfer in resting and contracting in vivo rat skeletal muscle. Theoretically, the rate constant should be the sum of the rate constants of the reactions catalyzing ATP-ADP exchange. In resting muscle, the conversion rate constant was 0.4 s Ϫ 1 and -ATP intrinsic T 1 was 1.7 s. The velocity of conversion was 3.8 mM s , respectively, but did not reach expected levels, i.e. the product of the ATP concentration with the sum of pseudo first-rate constants of the individual reactions. These conversion velocities should be higher than reverse creatine kinase velocities, previously measured to be 10 mM s Ϫ 1 in resting muscle and 7.5 mM s Ϫ 1 in contacting muscle and confirmed in this work. The discrepancy between expected and observed data could be due either to compartmentation of part of the -ATP in pools exchanging slowly with the bulk of cellular ATP, or to ADP binding to macromolecules thus preventing full ADP saturation during magnetization transfer. ©
Metabolic and mechanical properties of female rat skeletal muscles, submitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test. 31P-NMR was used to follow energy metabolism and pH. Mechanical performance was greatly improved in trained muscles. The oxidative capacity of the skeletal muscles was evaluated from the relationship between ADP calculated from the creatine kinase equilibrium and work and from the measure of the rate of phosphocreatine (PCr) resynthesis following exercise. In trained muscles, ADP production was lower per unit of mechanical performance, showing an improvement of oxidative metabolism. However, the PCr resynthesis rate was not modified. Slight acidosis and ATP depletion were observed from the beginning of the fatigue test. These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production. Our results indicate that muscle status improvement could be accompanied by ATP depletion and minimal acidosis during contraction: this would be of particular importance for objective evaluation of muscle regeneration processes and of gene therapy in muscle diseases. IMPROVEMENT OF MUSCULAR OXIDATIVE CAPACITY BY TRAINING IS ASSOCIATED WITH SLIGHT ACIDOSIS AND ATP DEPLETION IN EXERCISING MUSCLES XAVIER RAVALEC, NATHALIE LE TALLEC, FRANCOIS CARRE, MD, JACQUES D. de CERTAINES, PhD, and ELISABETH LE RUMEUR, PhDT h e major goals of endurance training are to increase the oxidative metabolic capacity of the skeletal muscle and its maximal mechanical performance. Endurance training has been shown to increase mechanical performance by decreasing the fatigue level'0p22,24 in association with the increase in mitochondrial number and in the activities in the enzymes involved in oxidative metabolism.3,7,10,12,22,24 These changes are accompanied by lower lactic acid production and higher lactate
The rate constant of the β‐adenosine triphosphate to β‐adenosine diphosphate conversion was measured using 31P nuclear magnetic resonance magnetization transfer in resting and contracting in vivo rat skeletal muscle. Theoretically, the rate constant should be the sum of the rate constants of the reactions catalyzing ATP–ADP exchange. In resting muscle, the conversion rate constant was 0.4 s−1 and β‐ATP intrinsic T1 was 1.7 s. The velocity of conversion was 3.8 mM s−1. During stimulation, phosphocreatine fell to 36% and ATP to 82% of initial values. The rate constant and velocity of β‐phosphoryl conversion increased to 0.8 s−1 and 6.3 mM s−1, respectively, but did not reach expected levels, i.e. the product of the ATP concentration with the sum of pseudo first‐rate constants of the individual reactions. These conversion velocities should be higher than reverse creatine kinase velocities, previously measured to be 10 mM s−1 in resting muscle and 7.5 mM s−1 in contacting muscle and confirmed in this work. The discrepancy between expected and observed data could be due either to compartmentation of part of the β‐ATP in pools exchanging slowly with the bulk of cellular ATP, or to ADP binding to macromolecules thus preventing full ADP saturation during magnetization transfer. © 1997 John Wiley & Sons, Ltd.
Kinetics of phosphoryl transfers from PCr to gamma-ATP and from beta-ATP to beta-ADP were measured by magnetization transfer in an in vivo 31P NMR experiment in working rat skeletal hind leg muscles. Two groups were examined. One group was submitted to a 6-week training program of treadmill running. The other group was composed of sedentary animals. Metabolic oxidative capacity and mechanical performance were improved greatly by training as shown previously. Phosphoryl transfer of PCr-->gamma-ATP or beta-ATP-->beta-ADP total fluxes were identical in resting trained and untrained muscles. Under stimulation, the flux of creatine kinase transfer was significantly inhibited by 23% compared with resting level in untrained muscles; by contrast, it was not inhibited and maintained at the high resting level in trained muscles. Thus physiological changes probably linked to a decrease of the production of anions, which could inhibit creatine kinase, were able to maintain creatine kinase flux. The flux of beta-ATP to beta-ADP transfer were enhanced largely in working muscles from 1.4+/-0.8 and 2+/-0.8 at rest to 4+/-1.6 and 6.6+/-2.7 mM s(-1) for untrained and trained muscles respectively; the effect was more pronounced in trained than in untrained muscles. These results showed an acceleration of phosphoryl turnover in working muscles after training, which could contribute to improve oxidative and mechanical performances. Such kinetic measurements of phosphoryl conversion may provide information on ATP turnover in pathophysiologic situations where ADP accumulates because of impaired ATP synthesis (mitochondrial myopathies, lower perfusion level).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.