Regulation of electrogenic anion secretion in normal and cystic fibrosis gallbladder mucosa

Abstract

Fluid and ion transport across biliary epithelium contributes to bile flow. Alterations of this function may explain hepatobiliary complications in cystic fibrosis (CF). We investigated electrogenic anion transport across intact non-CF and CF human gallbladder mucosa in Ussing-type chambers. In non-CF tissues, baseline transmural potential difference (PD), short-circuit current (Isc), and resistance (R) were ؊2.2 ؎ 0.3 mV (lumen negative), 40.7 ؎ 7.8 A/cm 2 , and 66.5 ؎ 9.6 ⍀ · cm 2 , respectively (n ‫؍‬ 14). The addition of forskolin (10 ؊5 mol/L) to the apical and basolateral baths and that of adenosine 5Ј-triphosphate (ATP) (10 ؊4 mol/L) to the apical bath induced significant increases in Isc by 8.0 ؎ 1.4 and 10.3 ؎ 1.8 A/cm 2 , respectively. Depletion of bathing solutions in Cl ؊ and HCO 3 ؊ significantly reduced baseline Isc and the forskolin-and ATPinduced increases in Isc. Anion secretion was stimulated by extracellular ATP via P2Y 2 purinoceptors, as indicated by the effects of different nucleotides on Isc and on 36 Cl efflux in cultured gallbladder epithelial cells. This effect was mediated by cytosolic calcium increase and Ca 2؉ /calmodulindependent protein kinase II, as ascertained by using inhibitors. In CF preparations, basal PD and Isc were lower than in non-CF, and the response to forskolin was abolished, whereas the response to ATP was enhanced (P F .05 for all). We conclude that electrogenic anion secretion occurs in human gallbladder mucosa under basal state and is stimulated by an adenosine 3Ј,5Ј-cyclic monophosphate (cAMP)-dependent pathway mediated by cystic fibrosis transmembrane conductance regulator (CFTR), and by exogenous ATP via a CFTR-independent pathway that is up-regulated in CF and involves P2Y 2 purinoceptors and a calciumdependent pathway. (HEPATOLOGY 1999;29:5-13.)

Altered hepatobiliary gene expressions in PFIC1: ATP8B1 gene defect is associated with CFTR downregulation

“…39 Alternatively, ATP8B1 defect could affect the transcriptional activity not only of FXR, 13 but also of other transcription factors, like HNF1, which regulate the tissue-specific expression of CFTR. 40 Because CFTR is a major determinant of hydroelectrolytic secretion in the biliary tract, 20,[41][42][43] CFTR downregulation may contribute to impaired bile secretion through bile inspissation in PFIC1. This would explain the typical ultrastructural abnormality of bile in PFIC1 termed "Byler bile", characterized by a coarsely granular appearance.…”

“…This may impair the contribution of cholangiocytes to bile secretion and also potentially explain some of the extrahepatic manifestations in PFIC1 and related disorders. The gallbladder, a site of high endogenous expression of ATP8B1 and of CFTR, 20,21,42 fully takes part to the regulation of the bile acid pool, 46 and thus may be of particular importance in the pathogenenesis of PFIC1.…”

Correction of CFTR malfunction and stimulation of Ca2+ -activated Cl− channels restore HCO 3− secretion in cystic fibrosis bile ductular cells

“…Purinergic nucleotides are present in bile in concentrations sufficient to activate purinergic receptors. 54 Stimulation of these receptors may promote anion transport both in biliary 18,21,22 and pancreatic 55 duct epithelial cells, at least transiently. 19,20 Interestingly, ATP stimulated HCO 3 Ϫ secretion only in the presence of elevated intracellular cAMP as previously shown.…”

“…In addition to cAMP-stimulated Cl Ϫ channels, Ca 2ϩ -activated Cl Ϫ conductances have also been described in both murine 19,20 and human biliary epithelial cells, 21,22 but their relationship to HCO 3 Ϫ secretion and their function in CFTR-deficient cells are unknown. We studied these relationships in both control and CFTR-deficient human bile duct cells.…”

Bioelectric Characterization of Epithelia from Neonatal CFTR Knockout Ferrets

“…High levels of CFTR mRNA have been shown to exist in the human and mouse gallbladder epithelium (5,34,35). In addition, non-CF human gallbladder epithelia have been shown to produce cAMP-inducible electrogenic Cl 2 secretion that is absent in CF tissues (36,37). Functional studies on ferret and pig CF and normal gallbladder epithelia have yet to be reported.…”