Endocrine Abstracts

Somatostatin and dopamine receptors are the major G_i-coupled receptors in somatotrope cells that inhibit hormone secretion from the anterior pituitary. Here, we adapted a novel fluorescence-based screening assay to characterize somatostatin and dopamine receptor signaling in a time-resolved manner. This minimal-invasive technique provides a robust and reliable read out for ligand-induced receptor activation in permanent cell lines and primary pituitary culture. The pituitary cell line AtT-20 expresses both sst2 and sst5 endogenously. Exposure of WT AtT-20 cells to the sst2- and sst5-selective agonists BIM23120 and BIM23268, respectively, promoted a PTX- and tertiapin-Q-sensitive reduction in fluorescent signal intensity, which is indicative of activation of G protein-coupled inwardly rectifying potassium (GIRK) channels. In contrast, exposure to BIM23926 (sst1-selective), L-796/778 (sst3-selective), or L-803/067 (sst4-selective) did not produce any change in fluorescent signal intensity. However, after heterologous expression of sst1, sst3, or sst4 receptors BIM23926 and L-796/778 but not L-803/087 promoted a reduction in fluorescent signal indicating that sst1 and sst3 receptors can also couple to GIRK channels. Similar activation of GIRK channels by dopamine in AtT-20 required overexpression of D2 dopamine receptors.

Disclosure: German Research Foundation.