PLASMA-MEMBRANE ORDER-PARAMETER IN PERIPORTAL AND PERIVENULAR HEPATOCYTES ISOLATED FROM ETHANOL-TREATED RATS

Hepatic ethanol (EtOH) metabolism has been assumed to involve hepatocy tes differently, according to their location in the hepatic acinus. Th is study's aim was to gain information or. plasma membrane (PM) order parameter in periportal (PP) and perivenular (PV) hepatocyte-enriched fractions isolated by a digitonin-collagenase perfusion technique from rats pair-fed for 6-8 wk liquid diets containing either EtOH or isoca loric carbohydrates. Fluorescence polarization (P) studies have been p erformed to measure PM order parameter of PP and PV hepatocytes cultur ed for 2-6 h on glass cover slips and labeled with -(trimethylamino)ph enyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), a specific probe for PM of living cells. Fluorescence polarization and microscopy indicated that TMA-DPH is a suitable probe to study PM order parameter in subconfluen t rat hepatocyte monolayers where it labeled, after a rapid incorporat ion, PM of cells. In pair-fed control rats, PM order parameter was low er in PP hepatocytes than in PV cells (P = 0.366 +/- 0.013 vs. 0.381 /- 0.021, respectively, P < 0.02; n = 7). In EtOH-treated rats, these zonal differences tended to disappear (P = 0.419 +/- 0.012 in PP cells vs. 0.417 +/- 0.007 in PV cells; n = 7). In addition, the order param eter was significantly higher either in PP or PV hepatocytes compared with pair-fed control animals (P < 0.002 and 0.003, respectively). A 3 0-min culture of cells in the presence of 40-200 mM EtOH significantly decreased the PM order parameter of hepatocytes isolated from pair-fe d control rats with respect to EtOH-treated animals both in PP and PV cells (P < 0.01 and 0.02, respectively; n = 4). Our data indicate that the order parameter of PM of hepatocytes is distributed along an acin ar gradient increasing from zone 1 to zone 3. Selective modification o f this gradient occurs after chronic EtOH exposure leading to a genera l increase of membrane order parameter, attenuation of zonal differenc es, and higher resistance to the fluidizing effect of EtOH in vitro.