In vivo P-31-MRS assessment of cytosolic [Mg2+] in the human skeletal muscle in different metabolic conditions

Cytosolic free [Mg2+] can be assessed in vivo by P-31-MRS from the chemical shift of beta-ATP. The reliability of in vivo measurements depends on the availability of appropriate in vitro calibration curves obtained by using s olutions that mimic the in vivo cytosolic conditions as far as possible, We build a semi-empiric equation that correlates the chemical shift of beta-A TP to free [Mg2+] taking into account the amount of Mg2+ bound to all other ligands in solution. Our experiments resulted in a reliable ten-parameters equation directly usable to assess the cytosolic free [Mg2+] of human skel etal muscle at rest, during work and recovery. Our experiments also resulte d in a new equation that allows the assessment of cytosolic pH from the che mical shift of Pi laking into account the measured free [Mg2+]. To perform simultaneous calculation of free [Mg2+] and pH in the skeletal muscle in di fferent metabolic conditions we developed a specific software package avail able on Internet (http://www.unibo.it/bioclin) together with another progra m based on the equation previously obtained to calculate cytosolic free [Mg 2+] in the human brain. The reliability and effectiveness of our equations and software were tested on the calf muscles of healthy volunteers at rest, during work and recovery. (C) 2000 Elsevier Science Inc. All rights reserv ed.