A time-resolved fluorometric (TRF) assay was developed for human galan
in receptors, subtype 1 (hGalR1), The galanin peptide was labeled with
a europium chelate, Eu3+-DTTA. Ligand binding was conducted in D98/Ra
ji cells expressing recombinant human GalR1 (hGalR1-D98/Raji) in monol
ayers in 96-well plates or in crude membrane preparations in 96-well f
ilter plates. Bound ligand was quantitated by dissociation-enhanced ti
me-resolved fluorometric measurement of Eu3+. Eu(3+-)galanin bound to
hGalR1 in a saturable manner with K-d values of 2.9 +/- 0.5 nM in whol
e cell assays and 0.23 +/- 0.03 nM in membrane assays, The affinities
of Eu3+-galanin for hGalR1 in both the whole cell and membrane assays
correlated very well with those of I-125-galanin. In addition, the bou
nd Eu3+-galanin could be competitively displaced from the receptors by
galanin peptide antagonists C7, M15, M35, and M40. In hGalR1-expressi
ng 293EBNA cells, Eu3+-galanin stimulated an increase in intracellular
Ca2+ concentration with a similar EC50 value as unlabeled galanin (4.
5 +/- 0.5 nM versus 4.2 +/- 0.3 nM), indicating that Eu3+ labeling did
not affect the functional activity of galanin, The galanin TRF assay
was employed in high throughput screening of combinatorial chemical li
braries. The sensitivity of this assay is comparable with that of I-12
5-galanin. The advantages of this assay include elimination of radioac
tivity, stability, low cost, speed, and amenability for automation.