The effect of buffer composition and deoxygenation on the concentration of ionized magnesium inside human red blood cells.

1. A method is described in which the concentration of ionized magnesium can be measured in intact red cells. The method uses an equilibrium dialysis technique originally developed by Ferreira & Lew (1976) and Flatman & Lew (1977) where the magnesium permeability of the red cell membrane is increased with the ionophore A23187. 2. The concentration of ionized magnesium in the oxygenated cells was found to be 0.39 mM and was not greatly affected by changes in the composition of the medium. 3. The concentration of ionized magnesium in deoxygenated cells showed more dependence on the composition of the medium. Values of 0.54 and 0.62 mM were found in cells incubated in Tris- and HCO3- buffered media respectively. The difference probably reflects increased competition between chloride and 2,3-diphosphoglycerate for common binding sites on haemoglobin in Tris-buffered cells. 3. Only a small increase of 0.16-0.22 mM was found in the concentration of ionized magnesium when the cells were deoxygenated. These changes are smaller than had been anticipated from estimates of the binding of ATP and 2,3-diphosphoglycerate to oxy- and deoxyhaemoglobin (Bunn, Ransil & Chao, 1971; Berger, Janig, Gerber, Ruckpaul & Rapoport, 1973; Gerber, Berger, Janig & Rapoport, 1973) and are unlikely to alter greatly the operation of magnesium-dependent metabolic or transport systems.