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 re cycling, and vesicular endoexocytotic processes. The aim of this study was to investigate the effect of a specific P13-K inhibitor, wortmann in, on bile secretion, cytoskeleton organization, and endotranscytotic pathways in rats. Methods: Isolated perfused rat liver (IPRL) and iso lated rat hepatocyte couplets (IRHCs) were used. Results: Wortmannin i nduced a 25% inhibition of basal bile flow in IPRL (P < 0.01). Horsera dish peroxidase biliary excretion in the IPRL was markedly decreased b y wortmannin. In IRHC incubated with 25 nmol/L wortmannin for 10 minut es at 37 degrees C, morphological studies showed early significant dil atation of bile canalicular lumen (P < 0.001). At short intervals (3 m inutes), uptake of the fluid-phase marker, Lucifer yellow, was markedl y 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 diso rganization of microfilaments. Conclusions: Wortmannin inhibits basal bile flow, endocytosis, and transcytotic transport of fluid-phase mark ers in the liver, and causes an early dilatation of the canalicular lu men and disorganization of microfilaments. These findings suggest that P13-K is involved in the regulation of vesicle trafficking, cytoskele ton organization, and the process of bile formation.