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 th awing. In the haemolysates the concentration of total Mg2+ (by atomic absorption spectrophotometry), free Mg2+ (by a Mg2+-sensitive electrod e) and ATP were determined. The increase in the free Mg2+ concentratio n was also measured when titrating the haemolysates with MgCl2. The ex periments yielded a total Mg2+ buffer capacity of 4.85 mM with a K-a o f 0.9 mM(-1), indicating that 2,3 bisphosphoglycerate was the main Mg2 + buffer in haemolysates of erythrocytes which had been ATP-depleted d uring preparation. The activity coefficient of free Mg2+ in erythrocyt es was the same as in the chloride-based calibration solutions.