Mag-Fura-2 tetrapotassium, a UV-excitable fluorescent Mg²⁺/Ca²⁺ indicator (Ex=334-360 nm, Em=510 nm), is used to determine Mg²⁺ and Ca²⁺ concentrations [1] [2].

Monitoring of Ca2+ release [1]: Incubate dispersed parotid acinar cells (e.g., acinar cells) with 8 μM Mag-fura-2 tetrapotassium for 30 min at 37°C. Wash cells twice with fresh HBSS-H without BSA. Precoat cell adhesive Cell-Tak on sample chambers. Transfer dye-loaded cells to the chambers and attach to the bottom. Mount the sample chambers on an inverted microscope (equipped with a 40x objective), and wash with BSA-free HBSS-H, followed by Mg2+/ATP-free ICM. Incubate acinar cells with Mg2+/ATP-free ICM containing 50 μg/mL saponin for 3-5 min at room temperature. Wash the cells with ICM containing Mg2+ and ATP, and incubate in the complete ICM for at least 5 min to allow complete filling of the intracellular Ca2+ stores. Alternately excite permeabilized cells, capture and digitize fluorescence emission at 510 nm using a digital imaging system, recording the 344 nm/360 nm ratio every 20 s. Note: ICM (intracellular-like medium) contains 125 mM KCl, 19 mM NaCl, 10 mM HEPES (pH 7.3 with KOH), 3 mM ATP, 1.4 mM MgCl2, 0.33 mM CaCl2, and 1 mM EGTA.