10th International Magnesium Symposium Schedule of Events

39
Cytosolic free [Mg2+] in the human calf muscle in different metabolic
conditions
Associate Professor Stefano Iotti, University of Bologna, Bologna, Italy.
iotti@med.unibo.it
Accurate knowledge of intracellular [Mg2+] is crucial for a deeper understanding of
cellular bioenergetics, and detecting changes of [Mg2+] that may alter critical
regulatory mechanisms causing abnormal metabolism. In the skeletal muscle,
variations of pH, phosphocreatine and inorganic phosphate concentrations influence
the complex multi-equilibrium system of the molecular species binding magnesium.
As a consequence [Mg2+] can change considerably in different metabolic conditions
such as rest, exercise and recovery. We compared the [Mg2+] assessed in vivo in
the human calf muscle by 31P MRS and calculated by a computer simulation in
different metabolic conditions. We studied 42 controls by a G.E. 1.5 T Signa System.
[Mg2+] was assessed from the chemical shift of beta-ATP (1). Computer simulation
was performed, by HYSS (HYperquad Simulation and Speciation) (2). We found by
31P-MRS a mean resting [Mg2+] of 0.32 mM. This value was used to calculate by
HYSS the total amount of magnesium in the muscle cells, which was 7 mM. The in
vivo assessment showed that during exercise and recovery [Mg2+] remarkably
changed, due to the predominant effect of pH. The plot of [Mg2+] as a function of pH
showed an exponential pattern with a sharp increase of [Mg2+] below pH 6.5.
Simulation by HYSS showed a much smaller increase of free [Mg2+] in the same pH
region. Results show that our model well describes the in vivo [Mg2+] of muscle cells
under different metabolic conditions, suggesting the existence of more Mg-binding
sites releasing Mg2+ at low pH.
1 Iotti S. et al. MRI 18, 607, 2000
2 Gans P. et al. Talanta 43, 1739, 1996