Membranes and phospholipids of liver mitochondria from chronic alcoholic rats are resistant to membrane disordering by alcohol.

Abstract

Using the spin probe 5-doxylstearic acid, we studied the structural perturbations of rat liver mitochondrial membranes produced by exposure to ethanol in vitro and by chronic ethanol feeding. The addition of ethanol in vitro to mitochondria from control animals appears to "fluidize" the membranes, as evidenced by a pronounced decrease in the order parameter. By contrast, in membranes from rats fed ethanol chronically, there was no effect on the order parameter. This resistance of the mitochondrial membranes from chronically intoxicated animals to the fluidizing effect of ethanol probably results from a change in the composition of the phospholipids, because the same differential response to ethanol was observed upon using vesicles of mitochondrial phospholipids extracted from control and chronically treated rats. In the presence of 0.025-0.1 M ethanol, a range that prevails in the blood of chronic alcoholics, the order parameter of mitochondrial membranes from rats fed ethanol was comparable to that of control membranes without ethanol in vitro. Analysis of extracted mitochondrial phospholipids showed that the cardiolipin from ethanol-fed animals had fatty acyl residues that are more saturated than those of controls. These findings point to the underlying molecular mechanism for our previous observation that mitochondria from chronic alcoholic rats are more resistant to uncoupling by ethanol at physiological temperature [Rottenberg, H Chronic ethanol ingestion by rats produces striking structural (1, 2) and functional (3, 4) aberrations of liver mitochondria. Although these changes are commonly ascribed to a damaging effect of chronic alcoholism on hepatic metabolism, we have recently suggested (5) that they might reflect an adaptation of the mitochondrial membranes to the presence of ethanol. In mitochondria from rats treated chronically with ethanol, respiration and ATPase activities are lower and more resistant to the stimulating effect of ethanol at physiological temperature (5). This latter effect is probably the result of the "fluidizing" effect ofethanol on phospholipid membranes (6). The resistance to the effect of ethanol in mitochondria from chronically intoxicated animals might result from a change in the membrane structure, as suggested by the shifts of the breaks in Arrhenius plots of both respiration and ATPase to higher temperatures, and by the lowering of the energy of activation of these membrane enzymes. We, therefore, sought to detect such structural changes by direct physical measurements in intact membranes and in their isolated lipids to discover whether the membranes become more "rigid" or more resistant to the fluidizing effect ofethanol, as suggested by our previous study (5). We employed the nitroxide spin labels 5-doxyl-and 12-doxylstearic acid as probes ofthe membrane lipid environment (7). The distribution of molecular orientations of the probe in the membrane is commonly expressed in terms of a calculated order parameter (8). Our EPR measurements with these probes directly ...

Decrease in microviscosity and cholesterol content of rat liver plasma membranes after chronic ethanol feeding.

“…Furthermore, the results in Table I suggest that the canalicular (with 5'-ND and GGTP as markers) and sinusoidal (with Na,K-ATPase as a marker) subfractions were equally enriched. Although it is unclear why the fluidity increase is observed only in PM and not in mitochondria or microsomes (4,5), it is noteworthy that Storch and Schacter (43) have reported a similar discrepancy between PM and microsomes after a starve-refeeding regimen.…”

“…The former possibility is unlikely, since the degree of mitochondrial and microsomal contamination (as assessed by marker enzymes) was similar in both groups of animals. In addition, chronic ethanol feeding has been shown not to increase the fluidity of hepatic mitochondria and microsomes (4,5). Furthermore, the results in Table I suggest that the canalicular (with 5'-ND and GGTP as markers) and sinusoidal (with Na,K-ATPase as a marker) subfractions were equally enriched.…”

“…A currently held view is that in vitro ethanol renders membranes more fluid and that chronic ethanol administration alters membrane lipid composition, which results in adaptation to the acute fluidizing effect. Spch an adaptation has been reported to occur in brain synaptosomes (2) and erythrocytes (3), as well as in liver mitochondria and microsomes (4,5). However, to our knowledge, there are no reports of the effect of chronic ethanol may exert part of its hepatotoxic effect via liver PM alteration, we carried out the present study to investigate the properties of liver PM isolated from rats chronically fed an ethanolcontaining diet.…”

Effect of short-chain primary alcohols on fluidity and activity of sarcoplasmic reticulum membranes

“…s h o r t -c h a i n primary alcohols affect the functional and structural states of several biological membranes (Chin Goldstein, 1977;Stokes & Harris, 1982;Waring et al, 1981;Swartz et al, 1974;Retig et al, 1977;Kondo & Kasai, 1973;Garda & Brenner, 1984).…”

Ethanol disordering of spin-labeled mouse brain membranes: correlation with genetically determined ethanol sensitivity of mice.

“…Waring et aL (15), using liver mitochondriafrom rats chronically treated with ethanol, found that measurements at 15TC revealed a difference in base-line order parameter that was not apparent at 37C. We did not see any difference in order parameter between membranes of LS and SS mice at temperatures between 30 and 39TC (Fig.…”