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FIGURE 2. Dose response of agonist-induced sst2 internalization. HEK-sst2 cells were treated with 1 nmol/L, 10 nmol/L, 100 nmol/L, 1 µmol/L, or 10 µmol/L of various agonists. Also included are cells treated with 100 nmol/L TOC plus 5 µmol/L Coy-14 or with 1 µmol/L TOC plus 50 µmol/L Coy-14. After 30 min of incubation with peptides, cells were processed for immunocytochemistry, and internalized sst2 was quantified. (A) Representative experiment with dose-response curves for various agonists inducing sst2 internalization. TOC, Y-DOTA-TATE, and I-Gal-S-TATE are considerably more potent in inducing sst2 internalization than is DTPA-octreotide. TOC-induced internalization is efficiently abolished by excess of Coy-14. (B) Representative immunofluorescence images of agonist-induced internalized sst2 using DTPA-octreotide and TOC. TOC is almost 2 orders of magnitude more potent in inducing sst2 internalization than is DTPA-octreotide.
