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 estimate1,2 or simulate3,4 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 preparations6,7, which have inherent uncertainties about true concentrations and sidedness of effects. Using a divalent cation ionophore8 and a newly developed method9,10 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 studies11–14) has three main buffer systems which bind nearly 90% of the total Mg present inside the cell in physiological conditions.