Magnesium and potassium status in healthy subjects as assessed by analysis of magnesium and potassium in skeletal muscle biopsies and magnesium in mononuclear cells.

Magnesium and potassium concentrations were determined in plasma, erythrocytes and urine collected during 24 h, and in percutaneous muscle biopsies obtained in 30 healthy subjects. Magnesium was also analyzed in mononuclear cells. Men, compared to women, showed a higher urinary excretion of magnesium (p less than 0.05). The magnesium contents in mononuclear cells correlated significantly with the concentrations of magnesium in muscle biopsies (r = 0.63; p less than 0.001) and with the urinary losses of magnesium (r = 0.40; p less than 0.05). A significant interrelationship between magnesium and potassium was found in striated muscle (r = 0.65; p less than 0.001), and the contents of potassium in muscle biopsies correlated significantly with the levels of potassium in plasma (r = 0.41; p less than 0.05). In a separate study the day-to-day variations for the magnesium and potassium parameters were investigated during 5 consecutive days in 7 healthy subjects. The coefficient of variation for magnesium in mononuclear cells was comparably low (8.0%), considering the wide range between the subjects. This indicates that magnesium in mononuclear cells might be a valuable parameter in longitudinal follow-up studies.