ALTERATION OF LIPID-COMPOSITION OF HEPATIC MEMBRANES ASSOCIATED WITH MANGANESE-BILIRUBIN INDUCED CHOLESTASIS

One hypothesis concerning the pathogenesis of manganese-bilirubin (Mn- BR)-induced cholestasis is that the molecular organization of the bile canalicular membrane is altered. The purpose of the present study was to evaluate lipid composition and fluidity of hepatic membranes durin g cholestasis in male Sprague-Dawley rats. To induce cholestasis, mang anese (Mn, 4.5 mg/kg, intravenously [iv]) was given 15 min before bili rubin (BR, 25 mg/kg, iv). The rats were killed 30 min after BR injecti on, at which time bile flow was decreased by approximately 40% compare d to control values. Liver cell plasma membranes enriched in canalicul ar fractions (BCM) and plasma membranes enriched in sinusoidal and lat eral fractions (PM), microsomes, mitochondria and cytosol were isolate d by differential centrifugation. Total lipids were extracted and meas ured colorimetrically. To assess fluidity, membranes were incubated in vitro with fluorescent probes [1,6-diphenyl-1,3,5-hexatriene and ethy l-ammonium-phenyl)-6-phenyl-1,3,5-hexatriene]. After Mn-BR treatment, BCM cholesterol incorporation increased markedly (about 3-fold) accomp anied by a decrease in fluidity. BCM phospholipid content was unaltere d by the cholestatic challenge. In PM-enriched fractions, the changes in cholesterol and phospholipid content after Mn-BR treatment were not statistically significant (P > 0.05) compared to controls. Furthermor e, the biochemical alterations in PM were not accompanied by changes i n membrane fluidity. These results support the hypothesis that altered lipid composition and fluidity of BCM are involved in the pathogenesi s of Mn-BR cholestasis. (C) 1998 Elsevier, Paris.