title: Hydrophobic bile salts inhibit gallbladder smooth muscle function via stimulation of GPBAR1 receptors and activation of KATP channels.
abstract: Hydrophobic bile salts are thought to contribute to the disruption of gallbladder smooth muscle (GBSM) function that occurs in gallstone disease, but their mechanism of action is unknown. The current study was undertaken to determine how hydrophobic bile salts interact with GBSM, and how they reduce GBSM activity. The effect of hydrophobic bile salts on the activity of GBSM was measured by intracellular recording and calcium imaging using wholemount preparations from guinea pig and mouse gallbladder. RT-PCR and immunohistochemistry were used to evaluate expression of the G protein-coupled bile acid receptor, GPBAR1. Application of tauro-chenodeoxycholate (CDC, 50-100 microm) to in situ GBSM rapidly reduced spontaneous Ca(2+) flashes and action potentials, and caused a membrane hyperpolarization. Immunoreactivity and transcript for GPBAR1 were detected in gallbladder muscularis. The GPBAR1 agonist, tauro-lithocholic acid (LCA, 10 microm) mimicked the effect of CDC on GBSM. The actions of LCA were blocked by the protein kinase A (PKA) inhibitor, KT5720 (0.5-1.0 microm) and the K(ATP) channel blocker, glibenclamide (10 microm). Furthermore, LCA failed to disrupt GBSM activity in Gpbar1(/) mice. The findings of this study indicate that hydrophobic bile salts activate GPBAR1 on GBSM, and this leads to activation of the cyclic AMP-PKA pathway, and ultimately the opening of K(ATP) channels, thus hyperpolarizing the membrane and decreasing GBSM activity. This inhibitory effect of hydrophobic bile salt activation of GPBAR1 could be a contributing factor in the manifestation of gallstone disease.
authors.affiliation: Department of Anatomy and Neurobiology, University of Vermont College of Medicine, 89 Beaumont Avenue, Burlington VT 05405, USA.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Lavoie
authors.forename: Onesmo B
authors.initials: OB
authors.lastname: Balemba
authors.forename: Cody
authors.initials: C
authors.lastname: Godfrey
authors.forename: Conall A
authors.initials: CA
authors.lastname: Watson
authors.forename: Galya
authors.initials: G
authors.lastname: Vassileva
authors.forename: Carlos U
authors.initials: CU
authors.lastname: Corvera
authors.forename: Mark T
authors.initials: MT
authors.lastname: Nelson
authors.forename: Gary M
authors.initials: GM
authors.lastname: Mawe
mesh_terms: D000818:Animals; D001647:Bile Acids and Salts / Q000502:physiology*; D005260:Female; D005704:Gallbladder / Q000294:innervation / Q000378:metabolism / Q000502:physiology*; D006168:Guinea Pigs; D057927:Hydrophobic and Hydrophilic Interactions; D054086:KATP Channels / Q000378:metabolism* / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009130:Muscle, Smooth / Q000294:innervation / Q000378:metabolism / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology
chemical_list: D001647:Bile Acids and Salts; C513561:Gpbar1 protein, mouse; D054086:KATP Channels; D043562:Receptors, G-Protein-Coupled