Total and free Mg2+ contents in erythrocytes: a simple but still undisclosed cell model.

The concentration of intracellular free Mg2+ ([Mg2+]i) in erythrocytes, measured by means of 31P NMR and using a dissociation constant for MgATP of 38-50 microM, amounted to 0.2 mM [Mg2+]i in the erythrocytes of various species, was not significantly different and was independent of their total Mg2+ content. The more probable value of [Mg2+]i using the more realistic KD of Mg ATP or the null-point method may amount to 0.4 mM [Mg2+]i in erythrocytes is lower than the [Mg2+]i in nucleated mammalian cell types. The lower [Mg2+]i may be caused by a different regulation of Mg2+ influx and Mg2+ efflux by intracellular Mg2+ in erythroblasts. Free and reversibly bound Mg2+ represent a Mg2+ buffer. The main Mg2+-binding substances are ATP and 2,3-bisphosphoglycerate (2,3-BPG). Total Mg2+ content in the erythrocytes of various species is correlated to the concentrations of ATP and 2,3-BPG. The changed Mg2+ level in erythrocytes during deoxygenation, maturation, cold storage, in Mg2+ deficiency and in sickle cell anemia was reviewed.