No differences were observed between MLCs and MSCs in either the magnitude or kinetics of the Ca2+ response to any of the nucleotides. When cultured

as described, both MSCs and MLCs developed an increase in transmembrane resistance by day 3 signifying the development of confluent monolayers with tight junctions (Fig. 4A). When mounted in an Ussing chamber, confluent MLCs Selleck RXDX-106 and MSCs monolayers exhibited a basal Isc, reflecting transepithelial secretion, which increased dramatically in response to the addition of ATP (100 μM) to the apical chamber (Fig. 4B,C). The nucleotide-stimulated Isc was significantly inhibited by the nonspecific Cl− channel blocker, 5-nitro-2-(-3-phenylpropylamino)-benzoic acid (NPPB), or by the Ca2+-activated Cl− channel blocker niflumic acid (Fig. 4C,F). Additionally, preincubation with the IP3 receptor blocker, 2-APB, significantly inhibited the ATP-stimulated increase in Iscin both MLC and MSC (Fig. 4C). In separate experiments, the effect of apical versus basolateral P2 receptor stimulation on the Isc was determined. For both MSCs and MLCs, an increase

in the Isc was observed when nucleotides were added to either chamber, consistent with functional expression of P2 receptors on both apical and basolateral membranes. The magnitude of the change in Isc was similar when nucleotides were added to either apical or basolateral compartments for all nucleotides tested except for UTP which caused a significantly greater increase in Isc when added apically versus basolateral selleck screening library addition. Thus, both MSCs and

MLCs express functional P2 receptors on both apical and basolateral membranes. Nucleotide binding selleck to P2 receptors causes an increase in [Ca2+]i, predominantly through an IP3 receptor-dependent mechanism, which stimulates Ca2+-activated Cl− channels, and results in transepithelial secretion. To our knowledge, these represent the first integrated Isc measurements of transepithelial secretion in mouse cholangiocytes. Furthermore, in MSC, which do not express CFTR, Ca2+-activated Cl− efflux in response to extracellular nucleotides represents the first secretory pathway clearly identified in these cells derived from the small intrahepatic ducts. In human biliary cells and normal rat cholangiocyte monolayers, mechanical stimulation,22 shear stress,13 and cell swelling secondary to hypotonic exposure,22 have all been identified as significant stimuli for ATP release. Studies were performed to determine if these mechanical stimuli result in a similar increase in the magnitude of ATP release in mouse cholangiocytes. First, in response to hypotonic exposure (33% dilution) to stimulate cell swelling, a rapid and large increase in ATP release was observed in both MLCs and MSCs (Fig. 5A). The magnitude of the response, which peaked within 30 seconds, was significantly greater in MSCs versus MLCs (Fig. 5A,C).