On the sensitivity of intact cells to perturbation by ethanol

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.

Rat synaptic membrane fluidity parameters after intermittent exposures to ethanol in vivo

Differentiated membrane alterations correlate with the development of functional tolerance or dependence during chronic alcohol intoxication in humans as well as in animals. In animal studies, a single period of continuous exposure was generally used. In humans, the consumption can be more episodic with heavier weekend drinking. How a heavy but intermittent alcohol exposure over 4 weeks affects the synaptic membrane fluidity and sensitivity was examined in male and female adult rats. No differences were seen between membranes from males and females. Alterations were found in the negative polar membrane region probed by TMA-DPH and the sensitivity to acute ethanol was significantly reduced in the DPH (lipid core) and TMA-DPH probed membrane regions. Tolerance to the hypothermic effect of ethanol has developed and could be correlated with the resistance of the membrane lipid core to ethanol. Intermittent exposures to ethanol, as continuous ones, can result in development of functional and membrane tolerance and in specific alterations in the fluidity of the polar part of the membrane, probably in relation with dependence.

Effects of ethanol on phospholipid acylation in rat erythrocytes: a model for a biochemical approach to membrane adaptation

Challenging intact erythrocytes from naive rats with ethanol resulted in dose-dependent decreases in rates of acylation of phosphatidylcholine and phosphatidylethanolamine. In erythrocytes from ethanol-treated animals, the responses were of lesser magnitude, indicating a lower sensitivity to ethanol. This relative resistance, typical of the state of tolerance, was not associated with increased baseline rates of acylation of PC and PE, nor with changes in fatty acid specificity of acylation reactions. Taken together, the data suggest that (1) intact rat erythrocytes represent a reliable and easily reproducible model for studying biochemical correlates of the adaptive response to ethanol; (2) phospholipid acylation reactions are implicated in the initial sensitivity and subsequent acquisition of tolerance to ethanol in membrane erythrocytes; (3) on the basis of the measured acylation reactions, rat erythrocytes appear to develop tolerance, but not dependence, to ethanol.