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

Hepatic ethanol (EtOH) metabolism has been assumed to involve hepatocytes differently, according to their location in the hepatic acinus. This 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 isocaloric carbohydrates. Fluorescence polarization (P) studies have been performed to measure PM order parameter of PP and PV hepatocytes cultured for 2-6 h on glass cover slips and labeled with 1-[4-(trimethylamino)phenyl]-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 subconfluent rat hepatocyte monolayers where it labeled, after a rapid incorporation, PM of cells. In pair-fed control rats, PM order parameter was lower 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 parameter was significantly higher either in PP or PV hepatocytes compared with pair-fed control animals (P < 0.002 and 0.003, respectively). A 30-min culture of cells in the presence of 40-200 mM EtOH significantly decreased the PM order parameter of hepatocytes isolated from pair-fed 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 acinar gradient increasing from zone 1 to zone 3. Selective modification of this gradient occurs after chronic EtOH exposure leading to a general increase of membrane order parameter, attenuation of zonal differences, and higher resistance to the fluidizing effect of EtOH in vitro.