Journal of Applied Physiology AJP: Endocrinology and Metabolism
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J Appl Physiol (February 28, 2003). doi:10.1152/japplphysiol.00589.2002
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Submitted on July 2, 2002
Accepted on January 28, 2003

ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery

David Bendahan1*, Graham J Kemp2, Magali Roussel1, Yann Le Fur1, and Patrick J Cozzone1

1 School of Medicine, Centre de Resonance Magnetique Biologique et Medicale, UMR CNRS 6612, Marseille, France
2 Department of Musculoskeletal Science, University of Liverpool, Liverpool, United Kingdom

* To whom correspondence should be addressed. E-mail: david.bendahan{at}medecine.univ-mrs.fr.

We used 31P magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of 8 healthy males (25-45 y), during brief (18 s) voluntary finger flexion exercise (0.67 Hz contraction at 10% MVC; 50/50 duty cycle) and 180 s recovery. Phosphocreatine (PCr) concentration fell 19±2% during exercise, then recovered with t1/2 = 0.24±0.01 min. Cell pH rose by 0.058±0.003 units during exercise as a result of H+ consumption by PCr splitting, which (assuming no lactate production or H+ efflux) implies a plausible non-Pi buffer capacity of 20±3 mmol (l intracellular water)-1 (pH unit)-1. There was thus no evidence of significant glycogenolysis to lactate during exercise. Analysis of PCr kinetics as a classical linear response suggests that oxidative ATP synthesis reached 48±2% of ATP demand by the end of exercise, the rest met by PCr splitting. Post-exercise pH recovery was faster than predicted, suggesting 'excess proton' production, peak value 0.6±0.2 mmol (l intracellular water)-1 at 0.45 min of recovery, which might be due to e.g. proton influx driven by cellular alkalinisation, or a small glycolytic contribution to PCr resynthesis in recovery.




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