Altered fluidity of liver plasma membranes following partial hepatectomy in rats.

The fluidity of liver plasma membranes was assessed during regeneration following partial hepatectomy in rats. Fluorescence polarization was measured using 1,6-diphenyl-1,3,5-hexatriene to evaluate the fluidity of liver plasma membranes. The fluorescence polarization value of liver plasma membranes of control rats was 0.189 +/- 0.005 (mean +/- SEM). The fluorescence polarization values decreased initially after a 70% hepatectomy [0.176 +/- 0.003 at 3 hr and 0.174 +/- 0.004 at 6 hr (P < 0.01)] at 3 and 6 hours, but then recovered to preoperative levels (0.181 +/- 0.004, 0.189 +/- 0.004, 0.189 +/- 0.003, 0.193 +/- 0.003, 0.200 +/- 0.002, 0.208 +/- 0.007, and 0.190 +/- 0.003 at 12, 24, 36, 48, 72, 96 hr, and 7 days, respectively). Flow cytometric analysis using anti-bromodeoxyuridine (BrdU) monoclonal antibody was used to investigate the cell kinetics of the regenerating liver after 70% hepatectomy. The proportion of S-phase incorporating BrdU was not increased at 6 or 12 hr, but it then increased to peak of 27.9 +/- 1.9% at 24 hr. Subsequently, at 48, 72, and 168 hr, the proportion decreased to 8.5 +/- 0.6, 5.9 +/- 0.3, and 1.0 +/- 0.1%, respectively. The ratio of phospholipid to cholesterol contents of liver plasma membranes following partial hepatectomy did not significantly change in spite of markedly altered membrane fluidity. Thus, the alteration of membrane function occurs in conjunction with the initiation of the regeneration process following partial hepatectomy. It is suggested that the alteration of membrane fluidity plays an important role in the homeostatic response for cell proliferation.