The Rat SSTR2 Somatostatin Receptor Subtype Is Coupled to Inhibition of Cyclic AMP Accumulation

The rat somatostatin receptor SSTR2 subtype has been cloned and expressed in Chinese Hamster Ovary (CHO) cells. Four different radioligands were used to determine the pharmacological properties of this somatostatin receptor subtype. [125ITyr11]S-14, [125ITyr25]S-28, and cyclo (D-Trp-Lys-Abu-Phe-MeAla-[125ITyr]) displayed comparable affinities for the SSTR2 subtype (∼100 pM). The affinity of a fourth radioligand, D-βNal-cyclo (Cys-[125ITyr]-DTrp-Lys-Val-Cys)-Thr-H2N, was approximately 10-fold lower (∼1000 pM) than the three other radioligands. Competition of [125I]S-14 with either S-14 or S-28 also revealed comparable IC50 values (250 pM). In CHO cells transfected with the SSTR2 cDNA, S-14 inhibited forskolin-stimulated cAMP accumulation by 75% in a dose-dependent fashion (EC50 = 350 pM).