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

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Abstract
A method was described in which the concentration of ionized Mg can be measured in intact red cells. The method uses an equilibrium dialysis technique originally developed by Ferreira and Lew and Flatman and Lew where the Mg permeability of the red cell membrane is increased with the ionophore A23187. The concentration of ionized Mg in oxygenated cells was 0.39 mM and was not greatly affected by changes in composition of the medium. The concentration of ionized Mg in deoxygenated cells showed more dependence on 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 reflected increased competition between Cl- and 2,3-diphosphoglycerate [2,3-DPG] for common binding sites on Hg in Tris-buffered cells. Only a small increase of 0.16-0.22 mM was found in the concentration of ionized Mg when the cells were deoxygenated. These changes were smaller than had been anticipated from estimates of the binding of ATP and 2,3-DPG to oxy- and deoxyhemoglobin and are unlikely to alter greatly the operation of Mg-dependent metabolic or transport systems.