Comparison of functional profiles at human recombinant somatostatin sst 2 receptor: simultaneous determination of intracellular Ca 2+ and luciferase expression in CHO‐K1 cells

Somatostatin (somatotropin release inhibiting factor; SRIF) acts via five G protein‐coupled receptors (sst 1 –sst 5 ) that modulate multiple cellular effectors. The aim of this study was to compare two functional effects of the human sst 2 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 pEC 50 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 (pEC 50 =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 ( r 2 =0.83 and 0.90, pEC 50 and E max , 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 sst 2 receptors in CHO‐K1 cells. The increase in luciferase is mediated via G i /G o while intracellular calcium increase is mediated by both G i /G o 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