Monitoring cytosolic free magnesium in cultured chicken heart cells by use of the fluorescent indicator Furaptra.

Cytosolic free magnesium concentration [Mg2+]i and its regulation were studied in cultured embryonic chicken heart cells by use of the fluorescent indicator 2-[2-(5-carboxy)oxazole]-5-hydroxy-6-aminobenzofuran-N,N,O-triacet ic acid (Furaptra). The intracellular location of Furaptra was confirmed by its complete release from cells upon addition of saponin. The basal [Mg2+]i, which averaged 0.48 +/- 0.03 mM (n = 31), increased 3-fold on perfusion with sodium-free solution. This increase could not simply be attributed to intracellular sodium-extracellular magnesium exchange because a similar increase in [Mg2+]i occurred with magnesium-free, sodium-free perfusion. Furthermore, the increase in [Mg2+]i was largely attenuated when calcium was removed from the sodium-free perfusate. Thus, a substantial part of the increase in [Mg2+]i that occurs upon sodium-free perfusion is dependent on an increase in cytosolic free calcium (intracellular sodium-extracellular calcium exchange). The data suggest that [Mg2+]i is altered by calcium, most likely due to a competition for intracellular binding sites.