Measurement of intracellular magnesium concentration in 3T3 fibroblasts with the fluorescent indicator Mag-indo-1

Mag-indo-1, a fluorescent probe for measuring intracellular magnesium concentration, was used in 3T3 fibroblasts with microspectrofluorometry. The complex emission fluorescence spectrum emitted by a single living cell was analyzed with a computerized method, making it possible to evaluate the contribution of each species of Mag-indo-1 to the total fluorescence. The dye self-association observed in solutions at high dye concentration was not encountered in cells. The model of equilibria of Mag-indo-1 (monomer form) with protons, magnesium, and protein was then applied to calculate the intracellular magnesium concentration. The spectral analysis evaluated the contribution of each fluorescent species of Mag-indo-1 (a deprotonated, a magnesium-bound, and a protein-bound form) and of the cell autofluorescence to the total cell fluorescence. This method permitted accurate and reproducible measurements of intracellular magnesium concentration. Finally, this method was applied to the measurement of intracellular magnesium concentration in a 3T3 fibroblast population in exponential growth phase.