Mag-Fluo-4 is a fluorescent magnesium indicator (Kd = 4.7 mM) and low-affinity calcium indicator (Kd = 22 uM) with absorbance/emission at 493/517 nm (high Mg2+) . The cell membrane-impermeant tetrapotassium salt form can be introduced into cells by microinjection. Unit size: 500 ug.