Plasma, cytosolic and membrane magnesium content in renal insufficiency

Plasma magnesium, cytosolic (lymphocytic) and membrane (erythrocytic) magnesium concentrations were determined in 15 controls with normal renal function compared to 12 patients with renal insufficiency (chronic glomerulonephritis, serum creatinine 2.5 +/- 0.8 mg/dl, mean +/- SD). Plasma magnesium concentrations were determined by atomic absorption spectroscopy (AAS), cytosolic free magnesium with the fluorescent indicator Mag-Fura-2, and membrane magnesium by AAS, referred to membrane protein content which was determined according to Bradford's method. Plasma magnesium was 0.91 +/- 0.08 mmol/litre in controls versus 0.95 +/- 0.09 mmol/litre in renal-insufficient patients. Cytosolic free magnesium content was 2.38 +/- 0.75 mmol/litre in controls and 2.61 +/- 0.35 mmol/litre in the renal-insufficient group. In the renal-insufficient group membrane magnesium concentrations were found to be significantly increased as compared to the control group (2.85 +/- 0.62 vs 0.53 +/- 0.22 mmol/g membrane protein, mean +/- SD, P < 0.05). The results show that cell membranes may be of special importance in renal insufficiency in avoiding magnesium overload of the cell and in keeping free cytosolic magnesium stores stable.