Transcytotic vesicle fusion is reduced in cholestatic rats - Redistribution of phospholipids in the canalicular membrane

Cholestasis, which affects phospholipid trafficking, therefore would be exp ected to alter canalicular membrane phospholipid composition and fluidity, as well as fatty acid composition of membrane phospholipid. These alteratio ns may affect transcytotic vesicle fusion and would be expected to cause va riety of cholestatic phenomena. The aim of this study was to determine the effect of cholestasis on transcytotic vesicle fusion, Sprague-Dawley rats w ith extrahepatic and intrahepatic cholestasis were prepared by bile duct li gation (6 hr or three days) and phalloidin infusion (0.4 mg/kg body weight) , respectively. Liposomes of phosphatidylserine/phosphatidylcholine were la beled with octadecyl rhodamine B chloride, Fusion of liposomes to canalicul ar membrane vesicle preparations from cholestatic and control rats was indu ced by the addition of calcium. The degree of fusion was evaluated by measu ring the increase in rhodamine fluorescence. Membrane phospholipid content also was analyzed. Rates of liposomal fusion to membranes from cholestatic rats were decreased compared to controls. The saturated/unsaturated and sat urated/polyunsaturated fatty acid ratios were increased in membrane phospha tidylcholine and decreased in membrane sphingomyelin from cholestatic rats. Cholesterol/phospholipid ratios were increased. Thus, in the presence of c holestasis, a redistribution of phospholipid species within canalicular mem branes is associated with decreased transcytotic vesicle fusion, Cholestasi s likely decreases membrane fluidity. The regulation of phospholipid specie s within hepatocellular membranes may play an important role in intrahepati c lipid transport.