The fluorescence polarization levels of liver cell membranes and plasma were analyzed to determine membrane fluidity following bile duct ligation (BDL) in rats. Fluorescence polarization was measured with a spectrofluorophotometer equipped with polarizers, using 1,6-diphenyl-1,3,5-hexatrien (DPH) as a probe. After bile duct ligation, liver cell membrane fluidity decreased significantly for up to 14 days after surgery (P < 0.001 on 3rd and 7th days). The polarization of the plasma in rats with BDL slightly but significantly increased compared to the levels in the control animals over the 14-day period following BDL. In addition, a small but significant correlation in the polarization levels between plasma and liver cell membranes (r = 0.362, P < 0.02) was observed. The co-incubation of BDL plasma with normal liver cell membranes resulted in a decrease in membrane fluidity, which suggested that BDL rat plasma had a direct effect on membrane fluidity. After a 70% hepatectomy, the polarization of the membranes from remnant livers in the BDL rats remained elevated relative to the sham-operated controls. It is thus concluded that the membrane fluidity of the livers in BDL rats decreases following bile duct ligation and does not increase after a 70% hepatectomy, presumably due to the increased plasma level of bilirubin.
Dynamic changes in liver plasma membrane fluidity caused by regeneration and atrophy were assessed in rats following portal branch ligation (PBL). The portal branch, which perfuses 70% of the liver, was ligated with 5-0 prolene, and liver plasma membranes were isolated by ultracentrifugation. The membrane fluorescence polarization was measured as an index of membrane fluidity using 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe dye. In nonligated lobes, a significant decrease in fluorescence polarization was observed 12 and 24 h after PBL (0.171 ± 0.004, p < 0.01 and 0.165 ± 0.005, p < 0.001, respectively) as compared to the controls (0.181 ± 0.002). The fluorescence polarization values then gradually returned to near control levels. In contrast, in the ligated lobes, the fluorescence polarization had increased by 12 hours after PBL (0.196 ± 0.002, p < 0.01), and remained significantly elevated (p < 0.01) for up to 1 week after PBL, gradually returning to control levels within 3 weeks. The membrane composition was also evaluated by analyzing the cholesterol/ phospholipid (C/P) ratio. A significant increase in the C/P ratio was detected in the ligated lobes 12 h and 3 days after PBL, but there was no significant difference in fluorescence polarization values between nonligated lobes and controls. These results suggest that alterations in membrane fluidity play an important role in the regenerative and atrophic processes of the liver following portal branch ligation.
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