PLASMA-MEMBRANE FLUIDITY DURING REGENERATION AND ATROPHY OF THE RAT-LIVER FOLLOWING PORTAL BRANCH LIGATION

Dynamic changes in liver plasma membrane fluidity caused by regenerati on 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 ultrace ntrifugation. The membrane fluorescence polarization was measured as a n index of membrane fluidity using 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe dye. In nonligated lobes, a significant decrease in fluo rescence polarization was observed 12 and 24 h after PBL(0.171 +/- 0.0 04, p < 0.01 and 0.165 +/- 0.005, p < 0.001, respectively) as compared to the controls (0.181 +/- 0.002). The fluorescence polarization valu es then gradually returned to near control levels. In contrast, in the ligated lobes, the fluorescence polarization had increased by 12 hour s after PBL (0.196 +/- 0.002, p < 0.01), and remained significantly el evated (p < 0.01) for up to 1 week after PBL, gradually returning to c ontrol levels within 3 weeks. The membrane composition was also evalua ted by analyzing the cholesterol/ phospholipid (C/P) ratio. A signific ant increase in the C/P ratio was detected in the ligated lobes 12h an d 3 days after PBL, but there was no significant difference in fluores cence polarization values between nonligated lobes and controls. These results suggest that alterations in membrane fluidity play an importa nt role in the regenerative and atrophic processes of the liver follow ing portal branch ligation.