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CELLULAR METABOLISM
Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
Submitted 18 January 2007 ; accepted in final form 21 March 2007
31P magnetic resonance spectroscopy provides the possibility of obtaining bioenergetic data during skeletal muscle exercise and recovery. The time constant of phosphocreatine (PCr) recovery (
PCr) has been used as a measure of mitochondrial function. However, cytosolic pH has a strong influence on the kinetics of PCr recovery, and it has been suggested that
PCr should be normalized for end-exercise pH. A general correction can only be applied if there are no intersubject differences in the pH dependence of
PCr. We investigated the pH dependence of
PCr on a subject-by-subject basis. Furthermore, we determined the kinetics of proton efflux at the start of recovery. Intracellular acidosis slowed PCr recovery, and the pH dependence of
PCr differed among subjects, ranging from 33.0 to 75.3 s/pH unit. The slope of the relation between
PCr and end-exercise pH was positively correlated with both the proton efflux rate and the apparent proton efflux rate constant, indicating that subjects with a smaller pH dependence of
PCr have a higher proton efflux rate. Our study implies that simply correcting
PCr for end-exercise pH is not adequate, in particular when comparing patients and control subjects, because certain disorders are characterized by altered proton efflux from muscle fibers.
31P magnetic resonance spectroscopy; skeletal muscle; oxidative capacity; mitochondrial function; intracellular pH
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