Secretin Receptors in a New Preparation of Plasma Membranes from Intrahepatic Biliary Epithelium

Abstract

Secretin is thought to cause choleresis by acting on a receptor expressed by bile duct epithelial cells. In this study, the receptor was characterized using a new preparation of intrahepatic bile duct plasma membranes. Hyperplastic biliary trees were obtained from 3-week bile duct-ligated rats. The biliary trees were homogenized, filtered, and subjected to an aqueous two-phase partition technique to yield highly purified plasma membranes (confirmed by a 14-fold enrichment in γ-glutamyl transpeptidase activity and a 10-fold enrichment in 125I-secretin binding). 125I-secretin bound saturably with high affinity and in a dose-dependent fashion ( K d = 1.3 ± 0.1 n M, B max = 273 ± 23 fmole/mg) to purified plasma membranes. The binding characteristics of secretin were most consistent with a single site receptor model. Competitive binding studies indicated that the secretin-related peptides glucagon, peptide histidine isoleucine, gastric inhibitory peptide, and growth hormone releasing factor did not inhibit binding. Vasoactive intestinal peptide (1 μ M) reduced maximal binding by 19 ± 1%. The GTP analogs guanylyl-imidodiphosphate and guanosine 5′- O-[3-thiotriphosphate] (1 μM) inhibited binding by 16 ± 2 and 13 ± 1%, respectively. In conclusion, secretin binds to a specific, high-affinity receptor in intrahepatic bile duct epithelium that is coupled to a G-protein-linked signal transduction system.