In vivo assessment of mitochondrial functionality in human gastrocnemius muscle by 31P MRS. The role of pH in the evaluation of phosphocreatine and inorganic phosphate recoveries from exercise.

In this study we compared the kinetics of phosphocreatine (PCr) and P(i) recovery, and their dependency on cytosolic pH in 38 normal individuals. Spectra were acquired during rest, work and recovery. A time resolution of 10 s was used to obtain detailed information. The kinetics of PCr and P(i) recovery almost overlapped when the lowest value of cytosolic pH reached during recovery (termed the minimum pH) was < 6.95, while they were completely dissociated when the minimum pH was > 6.95. This result is interpreted as indirect in vivo evidence of the kinetic control exerted by ADP on mitochondrial oxidation. Our results represent a rationale for new experimental conditions to be used in clinical routine studies of pathologies due to primary or secondary mitochondrial malfunction.