Investigation of Intracellular Magnesium Mobilization Pathways I Pc12 Cells B Simultaneous Mg-Ca Fluorescent Imaging

Objective and Methods: PC12 cells were loaded with a novel Mg indicator KMG-104 and Ca indicator fura-2, and intracellular Mg was studied in the endoplasmic reticulums (ERs), mitochondria, and Mg-ATP. Under coexistence of the two indicators, fluorescent signals of Mg and Ca can be measured separately. Mg release from the ER was investigated by photolysis of caged compounds. Results: Transient [Ca] _i increase by uncaging of caged Ca or caged IP ₃ or bath-application of caffeine (10 mM) induced no [Mg] _i increase. These results suggest that there is no mechanism for Mg release from the ER through ryanodine receptors or IP ₃ receptors. In order to investigate the possibility of Mg release from Mg-ATP by energy consumption, we depleted ATP by oligomycin, an inhibitor of mitochondrial ATP synthase. Treating with oligomycin (4 μM) for several minutes showed no change of [Mg] _i and [Ca] _i. Conclusions: This result shows that Mg-ATP is not a Mg store. Since, when cells were treated by an uncoupler FCCP (3 μM), [Mg] _i and [Ca] _i increased, we concluded that mitochondria participate in maintenance of intracellular Mg stores.