Buffering and activity coefficient of intracellular free magnesium concentration in human erythrocytes

Human erythrocytes either untreated or Mg2+(-)loaded by means of A23187 in the presence of 3 or 12 mM MgCl2 were haemolysed by freezing and thawing. In the haemolysates the concentration of total Mg2+ (by atomic absorption spectrophotometry), free Mg2+ (by a Mg2+(-)sensitive electrode) and ATP were determined. The increase in the free Mg2+ concentration was also measured when titrating the haemolysates with MgCl2. The experiments yielded a total Mg2+ buffer capacity of 4.85mM with a Ka of 0.9 mM-1, indicating that 2,3 bisphosphoglycerate was the main Mg2+ buffer in haemolysates of erythrocytes which had been ATP-depleted during preparation. The activity coefficient of free Mg2+ in erythrocytes was the same as in the chloride-based calibration solutions.