ERYTHROCYTE MEMBRANE. EFFECTS OF AGE AND CHRONIC ETHANOL TREATMENT

Chronic ethanol consumption was demostrated to affect cell membrane lipid composition and fluidity. Studies on red blood cell (RBC) membrane of alcoholics showed a decrease in sialic acid content and a disorganization of the outer membrane leaflet. In addition ageing seems to affect RBC survival in circulating blood and to modify the presence of sialic acid on the outer surface of RBC membrane. In order to study the biochemical and biophysical properties of RBC membrane and the possible differences in the adaptive capability to ethanol chronic exposure during ageing we considered the membrane composition and the surface electric charge density. Albino male rats (Crl:(WI)BR Charles River Italiana), aged 2 months (young) and 7 months (adult) at the time of the experiment, were divided in two groups (ethanol-treated and control) and fed for 24 days a liquid diet (Lieber - DeCarli formula), in which ethanol or carbohydrates represented 36 % of the caloric content. RBC membranes were prepared and analyzed as previously reported (Monticelli et al. 1992). To estimate the membrane glycoprotein content, the defatted residue was assayed for neutral sugars and for sialic acid. Cell electrophoretic mobility measurements (MEF) were performed on RBC immediately after collected in a horizontal cylindrical capillary by the microscope method; electric surface charge density was calculated both assuming RBC to be spherical and using a flat plate model. Our experiments showed that ethanol treatment does not affect the electrophoretic mobility and the electric surface charge density of RBC, which increase in adult animals aside from treatment. Since electric surface charge is due to the presence of sialic acid on the outer surface of the membrane as expected after MEF experiments, gangliosidic sialic acid resulted not affected by ethanol treatment but it seems to be lower in adult treated animals than in the other groups. Nevertheless our data seem to indicate an increase of glycoprotein sialic acid in adult rats. According to the decreased galactosyltranspherase activity found in the enterocyte microsomes and in sinaptosomes of the same animals (Omodeo-Salè et al. 1994, Lindi et al. 1995), the glycoprotein neutral hexose content of RBC decreases while glycolipid neutral hexose content increases indicating that ethanol affects differently the various enzymatic systems. In conclusion our experiments underlined the ethanol effect on membrane composition suggesting adult rat membranes react more than the young. It is not the ethanol but ageing exerting effects on RBC electrophoretic mobility. Lindi et al. (1995) Alcohol: in press. Monticelli et al. (1992) Riv. It. Sostanze Grasse 67: 507. Omodeo-Salè et al. (1994) Alcohol 11: 301