The PICM-19 cell line as an in vitro model of liver bile ductules: effects of cAMP inducers, biopeptides and pH.

The PICM-19 fetal liver cell line was isolated from the primary culture and spontaneous differentiation of pig epiblast cells, i.e. embryonic stem cells. PICM-19 cells were induced to differentiate into mostly ductular formations by culturing at pH 7.6-7.8. The ductules were functionally assayed by treatment with cAMP inducing agents and bioactive peptides reported to influence the secretory activity of liver bile ductules. The secretory response of the cells was assessed by qualitative or quantitative measurement of the cross-sectional area of the ductal lumens and the appearance of biliary canaliculi in between PICM-19 cells that had formed monolayers instead of ducts. Forskolin (10 microM) and 8-bromoadenosine 3':5'-cyclic monophosphate (bcAMP; 2 mM) stimulated fluid transport and expansion of ductal structures in 15-20 min and stimulated the appearance and expansion of biliary canaliculi in 30-60 min. Cholera toxin (50 ng/ml) stimulates fluid transport in both ductules and canaliculi in 1-2 h, while 8-bromoguanosine 3':5'-cyclic monophosphate (bcGMP; 2 mM) stimulated only biliary canaliculi in 2 h. Glucagon (1.4 nM) produced a similar response in 5-10 min in ductal structures only, but the response was transitory and was almost completely reversed within 30 min. Secretin (100 pM) and vasoactive intestinal peptide (75 pM) produced a sustained response with maximal ductal lumen expansion occurring in 5-10 min and neither had an immediate effect on canaliculi. Somatostatin (0.5 microM) and gastrin (1 microM) caused marked reduction or disappearance of ductal lumens in 30-60 min, but was ineffective in reversing secretin (100 nM)-induced duct distension. Application of the adrenergic agonists, epinephrine, isoproterenol, and phenylephrine (100 microM), resulted in the complete shrinkage of ductal lumens in 20-30 min. A shift to pH 7.0-7.2 resulted in almost complete reduction of ductal lumens, while a shift to pH 7.8-8.0 resulted in expansion, although not full expansion, of the ductal lumens. PICM-19 bile duct cultures were positive for cytokeratin-7, aquaporin-1 and aquaporin-9 by Western blot analysis. The amounts of these proteins increased in the cultures as differentiation proceeded over time. Transmission electron microscopy revealed that the ductal structures were usually sandwiched between SIM mouse, thioguanine- and ouabain-resistant (STO) feeder cells that had produced a collagen matrix. Also, the ductular PICM-19 cells possessed cilia, probably occurring as a single cilium in each cell, that projected into the lumens of the ducts. The results indicated that the in vitro-produced ductal structures of the PICM-19 cell line are a functional model for biliary epithelium.