title: ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery.
abstract: We used (31)P-magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of eight healthy men (25-45 yr), during brief (18-s) voluntary finger flexion exercise (0.67-Hz contraction at 10% maximum voluntary contraction; 50/50 duty cycle) and 180-s recovery. Phosphocreatine (PCr) concentration fell 19 +/- 2% during exercise and then recovered with half time = 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-P(i) 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 classic linear response suggests that oxidative ATP synthesis reached 48 +/- 2% of ATP demand by the end of exercise; the rest was met by PCr splitting. Postexercise pH recovery was faster than predicted, suggesting "excess proton" production, with a peak value of 0.6 +/- 0.2 mmol/l intracellular water at 0.45 min of recovery, which might be due to, e.g., proton influx driven by cellular alkalinization, or a small glycolytic contribution to PCr resynthesis in recovery.
authors.affiliation: Faculté de Médecine, Centre de Resonance Magnetique Biologique et Medicale, Unité Mixte de Recherche 6612 Centre National de la Recherche Scientifique, Marseille 13005, France. david.bendahan@medecine.univ-mrs.fr
authors.forename: David
authors.initials: D
authors.lastname: Bendahan
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Kemp
authors.forename: Magali
authors.initials: M
authors.lastname: Roussel
authors.forename: Yann Le
authors.initials: YL
authors.lastname: Fur
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Cozzone
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000328:Adult; D015444:Exercise / Q000502:physiology*; D005385:Fingers; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010725:Phosphocreatine / Q000378:metabolism; D011522:Protons; D013997:Time Factors
chemical_list: D011522:Protons; D010725:Phosphocreatine; D000255:Adenosine Triphosphate