Magnesium content of plasma, cytosol and cell membranes in incipient renalinsufficiency

The concentration of magnesium was determined in plasma, cytosol (lymphocyt es) and cell membranes (erythrocytes) of 15 control persons with a normal r enal function and of 12 patients with a renal insufficiency due to chronic glomerulonephritis (serum creatinine 2.5 +/- 0.8 mg%, mean +/- SD). Plasma magnesium concentrations were measured by atomic absorption spectroscopy, f ree magnesium of the cytosol was determined by photometry using the fluores cence indicator mag-fura-2. Membrane magnesium was measured by atomic absor ption spectroscopy, too, and was referred to the membrane protein content, that was measured according to Bradford's method. Plasma magnesium concentr ation was 0.91 +/- 0.08 mmol/l in controls versus 0.95 +/- 0.09 mmol/l in r enal insufficient patients. Free intracellular magnesium content was 2.38 /- 0.75 mmol/l in healthy persons and 2.61 +/- 0.35 mmol/l in patients. In the group of renal insufficient patients membrane magnesium concentrations were found significantly higher than compared to the control persons (2.85 +/- 9.62 versus 0.53 +/- 0.22 mmol/g membrane protein, mean +/- SD, p < 0.0 1). These results show that cell membranes are of special importance in ren al insufficiency to avoid a magnesium overload of the cytosol and to keep c onstant the intracellular concentration of foe magnesium.