Use of ionophore A23187 to measure and to control free and bound cytoplasmic Mg in intact red cells

Abstract

CYTOPLASMIC magnesium, whether free or complexed to nucleotides, has a fundamental physiological role as an essential cofactor for many cell enzymes, particularly those concerned with glycolysis, respiration and membrane transport. Various ingenious procedures have been applied to estimate^1,2 or simulate^3,4 intracellular conditions in relation to Mg but, because it is impossible to assess and control Mg²⁺ in the intact cell, most research on Mg requirements for metabolism and transport has used lysed cells⁵ and broken membrane preparations^6,7, which have inherent uncertainties about true concentrations and sidedness of effects. Using a divalent cation ionophore⁸ and a newly developed method^9,10 we have investigated Mg buffering in intact human red blood cells and have found that the fresh, oxygenated, inosine-fed cell (a condition frequently used for ion transport studies^11–14) has three main buffer systems which bind nearly 90% of the total Mg present inside the cell in physiological conditions.