Comparison of functional profiles at human recombinant somatostatin sst2 receptor: simultaneous determination of intracellular Ca2+ and luciferase expression in CHO‐K1 cells

Somatostatin (somatotropin release inhibiting factor; SRIF) acts via five G protein‐coupled receptors (sst1–sst5) that modulate multiple cellular effectors. The aim of this study was to compare two functional effects of the human sst2 receptor stably expressed in CHO‐K1 cells in a single experiment using a duplex assay for intracellular calcium and serum response element (SRE)‐driven luciferase expression. Intracellular calcium was measured using a fluorometric imaging plate reader II (FLIPR II). SRIF‐14 rapidly and transiently increased intracellular calcium with a pEC50 of 8.74±0.03 (n=52). At 5 h after FLIPR II measurements, luciferase expression was determined. SRIF‐14 concentration‐dependently increased luciferase expression (pEC50=9.06±0.03, n=52). Natural and synthetic agonist/antagonist ligands for SRIF receptors were tested in the duplex assay. Correlation of agonist potencies and efficacies between the two responses were significant (r2=0.83 and 0.90, pEC50 and Emax, respectively). Pertussis toxin pretreatment reduced SRIF‐14/octreotide‐mediated intracellular calcium increases by 45–47% and luciferase expression by 95–98%. Thapsigargin pretreatment abolished the SRIF‐14/octreotide‐mediated intracellular calcium increase but had no effect on luciferase expression. In conclusion, SRIF stimulates an increase in intracellular calcium and SRE‐luciferase expression via human sst2 receptors in CHO‐K1 cells. The increase in luciferase is mediated via Gi/Go while intracellular calcium increase is mediated by both Gi/Go proteins and pertussis toxin‐insensitive G proteins, and is mainly via release of calcium from intracellular stores. SRIF ligands display a similar recognition profile suggesting that the ligand/receptor/G protein/effector interaction is similar for the two parameters. British Journal of Pharmacology (2004) 142, 150–160. doi:10.1038/sj.bjp.0705735