The two subtype 1 somatostatin receptors of rainbow trout, Tsst sub(1A) and Tsst sub(1B), possess both distinct and overlapping ligand binding and agonist- induced regulation features

• Published in: Comparative Biochemistry and Physiology, Part B: Biochemistry and Molecular Biology Vol. 138; no. 3; pp. 295 - 303
• Main Authors: Gong, J-Y, Kittilson, J D, Slagter, B J, Sheridan, MA
• Format: Journal Article
• Language: English
• Published: 01.07.2004
• Subjects: Freshwater; Oncorhynchus mykiss
• ISSN: 1096-4959
• DOI: 10.1016/j.cbpc.2004.04.005

In the present study, two isoforms of somatostatin receptor subtype one, previously obtained from the brain of rainbow trout, Tsst sub(1A) and Tsst sub(1B), were stably transfected in the Chinese hamster ovary cell line (CHO-K1) and their binding properties were characterized. High affinity binding of somatostatin by expressed receptors was saturable and ligand selective. Both Tsst sub(1A) and Tsst sub(1B) preferentially bound peptides derived from preprosomatostatin I (PPSS I; e.g. SS-14-I) over those derived from PPSS II (containing Tyr, Gly super(10)-SS-14-I at their C-terminus; e.g. SS-25-II). The rank order of ligand affinities for Tsst sub(1A) was SS-28-I>SS-14-I>SS-26-I>>SS-28- II>SS-14-II>SS-25-II. The rank order for Tsst sub(1B) was SS-14-I>SS-28-I>SS-26- 1>>SS-28-II>SS-25-II>SS-14-II. Agonist-induced regulation of Tsst sub(1A) and Tsst sub(1B) was also investigated. After 30 min of SS-14-I exposure, both Tsst sub(1A) and Tsst sub(1B) underwent rapid internalization; ca. 60% of membrane Tsst sub(1A) was internalized and only about 40% of membrane Tsst sub(1B) was internalized. Prolonged agonist exposure (up to 48 h) induced up-regulation of membrane-expressed Tsst sub(1A), but had no effect on Tsst sub(1B). These results indicate that Tsst1s display both distinct and overlapping ligand binding and agonist-induced regulation features. Such features may form the basis of ligand- selection and have important consequences on target organ responsiveness.