Calcium and magnesium contents of mammalian erythrocyte membranes.

Calcium and magnesium contents of whole erythrocytes and of erythrocyte membranes (stroma) were determined by atomic absorption technique on five mammalian species, man, rabbit, pig, cow and dog. In every species, the magnesium content of the whole erythrocyte is predominantly higher than the calcium content. Of the total magnesium, about 2-6% are localized in the membrane, whereas 40-86% of the whole cell calcium are found in the membrane. Except that the magnesium content of bovine erythrocyte is remarkably lower (about 1/7) than those of the other species, there seems to be no big species difference in these cation contents in the whole erythrocytes. The amounts of calcium localized in the membrane were found to be in a range of 1.5-2.6 •~ 10-18 mole per cell. The membrane magnesium contents vary considerably among the species examined and fall in a range of 1.6 (cow) -12 (dog) •~ 10-18 mole per cell, with the intermediate values on the other three species of 4.0, 4.1 and 5.6 x 10-18 mole per cell. The membrane Mg/Ca molar ratios range between 0.65-6.5. Intracellular concentrations of calcium and magnesium were calculated from the differences between the amounts in the whole cell and those in the membrane, assuming that no release of these cations occurs in the course of preparation of stroma.