Differential in vitro effects of ethanol on glycerolipid acylation and biosynthesis in rat reticulocytes.

Earlier reports have shown that, in human and rat red blood cells (RBC), ethanol modulates acylation reaction sin several membrane glycerolipid components. Little is known, however, about the kinetics and the mechanisms involved in the acylation changes. In the present study, we show that short-term in vitro exposure of intact rat reticulocytes to ethanol differentially modifies within minutes the incorporation of [3H]oleic acid in glycerolipids. A concentration-dependent inhibition of acyl incorporation was measured in phosphatidylcholine (PC) and phosphatidylethanolamine (PE). This effect did not involve inhibition of the corresponding acyltransferase activities and is likely to be due to ethanol-dependent decreases in phospholipase activities. In contrast, ethanol markedly stimulated [3H]oleic acid incorporation in phosphatidic acid (PA), diacylglycerol (DG) and, to a lesser extent, in triacylglycerol (TG). To determine the mechanisms of the latter increases, reticulocytes were pulsed with [14C]glycerol and assayed as a function of time for labeled biosynthetic precursors and products. We observed a very close correlation between time courses and amplitudes of the ethanol stimulation of acylation and biosynthesis reactions, suggesting that stimulation of acylation in PA, DG and TG is causally related at least partly to their increased biosynthesis. Further studies revealed that increases in glycerolipid acylation and biosynthesis in reticulocytes were: (a) readily reversible upon ethanol withdrawal; (b) detectable for clinically relevant concentration (50 mM) of ethanol; and (c) associated with concomitant increases in cell resistance to hemolysis. These changes may be relevant to the development of tolerance to ethanol.