Alteration of the mitochondrial membrane potential by CPZ was prevented by cotreatment with NAC, suggesting a role of ROS. Similar alterations were observed in HepaRG cells treated with 5 mM H2O2 starting at 30 minutes (data not shown). F-actin cytoskeleton, which is one of the primary targets of oxidative stress, was visualized by phalloidin fluoprobe labeling. Untreated cells showed pericanalicular location of F-actin and

large bile canaliculi with rounded shape, whereas 50 μM CPZ-treated PF-01367338 cell line cells exhibited a different distribution with lesser pericanalicular F-actin, retraction, and decreased surface area of bile canaliculi (Fig. 2B). Quantification of bile canalicular surface area and intensity of F-actin in the pericanalicular region showed up to 28% and 26% decrease, respectively, after CPZ exposure. To assess the effect of CPZ on TA efflux, cells were incubated with [3H]-TA for 30 minutes and then treated for another 30 minutes with 50 μM CPZ in standard buffer or Ca2+ and Mg2+-free

buffer. Radiolabeled TA has been measured in these two different buffers and in the cells to determine Selleck Y 27632 canalicular and basolateral efflux as well as intracellular accumulation of TA (7). A 25% increase in TA efflux was noticed in untreated HepaRG cells when canalicular tight junctions were disrupted (Ca2+ and Mg2+-free buffer), indicating that bile canaliculi correspond to a delimited closed compartment in these cells (data not shown). After 30 minutes of

treatment with CPZ, a 32% intracellular accumulation of TA was observed; it was associated with 35% decrease in canalicular efflux whereas basolateral efflux remained unchanged (Fig. 3A). These data support the conclusion that intracellular accumulation of TA was caused by a decrease of canalicular efflux rather than a diminution of basolateral efflux. Then the effects of CPZ in TA efflux were measured at different timepoints (0-6 hours) in standard buffer (Fig. 3B). The Ca2+ and Mg2+-free buffer was excluded because an incubation exceeding 30 minutes with this buffer caused increased cell death. No efflux inhibition was observed selleck before 30 minutes, whereas maximum inhibition occurred after 2 hours, with a 2-fold TA intracellular accumulation in CPZ-treated HepaRG cells. The CPZ-induced decrease of [3H]-TA efflux was abolished when cells were cotreated with CPZ and NAC; this result showed the involvement of oxidative stress in TA accumulation in CPZ-treated HepaRG cells. Because intracellular accumulation of TA was measured after treatment with CPZ in a standard buffer and that bile canaliculi were at least partially closed in control HepaRG cells, this accumulation could represent bile canalicular storage in addition to intracellular accumulation. To verify this hypothesis, bile canaliculi were disrupted by 5-minute incubation in Ca2+ and Mg2+-free buffer23 after a 2-hour treatment with CPZ.