Regulation of endocytic-transcytotic pathways and bile secretion by phosphatidylinositol 3-kinase in rats

Background & Aims: Phosphatidylinositol 3-kinases (P13-K) are a family of enzymes that play key roles in control of cell growth, membrane recycling, and vesicular endoexocytotic processes. The aim of this study was to investigate the effect of a specific P13-K inhibitor, wortmannin, on bile secretion, cytoskeleton organization, and endotranscytotic pathways in rats. Methods: Isolated perfused rat liver (IPRL) and isolated rat hepatocyte couplets (IRHCs) were used. Results: Wortmannin induced a 25% inhibition of basal bile flow in IPRL (P < 0.01). Horseradish peroxidase biliary excretion in the IPRL was markedly decreased by wortmannin. In IRHC incubated with 25 nmol/L wortmannin for 10 minutes at 37 degrees C, morphological studies showed early significant dilatation of bile canalicular lumen (P < 0.001). At short intervals (3 minutes), uptake of the fluid-phase marker, Lucifer yellow, was markedly decreased by exposure to wortmannin (P < 0.001). At longer times (20 minutes), Lucifer yellow was retained in basolateral area of IRHC as compared with control cells, where the marker was rapidly transported to the pericanalicular area. In IRHC, wortmannin induced a marked disorganization of microfilaments. Conclusions: Wortmannin inhibits basal bile flow, endocytosis, and transcytotic transport of fluid-phase markers in the liver, and causes an early dilatation of the canalicular lumen and disorganization of microfilaments. These findings suggest that P13-K is involved in the regulation of vesicle trafficking, cytoskeleton organization, and the process of bile formation.