CALCIUM GREEN-5N, A NOVEL FLUORESCENT-PROBE FOR MONITORING HIGH INTRACELLULAR FREE CA2-BRAIN NEURONS( CONCENTRATIONS ASSOCIATED WITH GLUTAMATE EXCITOTOXICITY IN CULTURED RAT)

We describe here the properties of calcium green-5N (CG5N), a novel Ca 2+-sensitive fluorescent probe. CG5N binds Ca2+ with an affinity of 4. 29 +/- 0.67 muM. Ca2+ binding is associated with a 14.7-fold increase in fluorescence. Mg2+ binds to CG5N with an affinity of 5 mM but produ ces a very small change in fluorescence. Using CG5N [Ca2+]i Was record ed in single cultured neurons from fetal rat forebrain. Glutamate toge ther with glycine increased [Ca2+]i by 1.17 +/- 0.15 muM. Pretreating cells with 5 mM potassium cyanide significantly potentiated the respon se to glutamate, resulting in a mean increase of 8.8 +/- 2 muM. These results demonstrate that CG5N is a useful indicator for measuring very large changes in [Ca2+]i in neurons.